Ebook Wallach''s interpretation of diagnostic tests (10th edition): Part 1

Wallach’s
Interpretation of Diagnostic Tests
Pathways to Arriving at a Clinical Diagnosis
TENTH EDITION


Wallach’s
Interpretation of Diagnostic Tests
Pathways to Arriving at a Clinical Diagnosis
TENTH EDITION
Edited by

Mary A. Williamson, MT (ASCP), PhD
Vice President, Scientific Affairs & Laboratory Operations
ACM Medical Laboratory
Rochester, New York
Former Assistant Professor
Department of Pathology
University of Massachusetts Medical School
Worcester, Massachusetts

L. Michael Snyder, MD
Professor
Department of Medicine and Pathology
University of Massachusetts Medical School
UMass Memorial Medical Center
Worcester, Massachusetts
Chief Medical Officer
Quest Diagnostics MA, LLC

Marlborough, Massachusetts


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Library of Congress Cataloging-in-Publication Data Wallach's interpretation of diagnostic tests. — Tenth edition / edited by Mary
A. Williamson, L. Michael Snyder.
p. ; cm.
Includes bibliographical references and index.
ISBN 978-1-4511-9176-9 (paperback : alk. paper)
I. Williamson, Mary A., editor. II. Snyder, L. Michael, editor.

[DNLM: 1. Clinical Laboratory Techniques. 2. Diagnostic Techniques and Procedures. QY 25]
RB38.2
616.07'56—dc23
2014012353
Care has been taken to confirm the accuracy of the information presented and to describe generally accepted practices. However, the
authors, editors, and publisher are not responsible for errors or omissions or for any consequences from application of the information in
this book and make no warranty, expressed or implied, with respect to the currency, completeness, or accuracy of the contents of the
publication. Application of this information in a particular situation remains the professional responsibility of the practitioner; the clinical
treatments described and recommended may not be considered absolute and universal recommendations.
The authors, editors, and publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in
accordance with the current recommendations and practice at the time of publication. However, in view of ongoing research, changes in
government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the
package insert for each drug for any change in indications and dosage and for added warnings and precautions. This is particularly
important when the recommended agent is a new or infrequently employed drug.
Some drugs and medical devices presented in this publication have Food and Drug Administration (FDA) clearance for limited use in
restricted research settings. It is the responsibility of the health care provider to ascertain the FDA status of each drug or device planned
for use in his or her clinical practice.
987654321


I am deeply grateful to my parents Priscilla and Thomas Williamson for their
unconditional love. Sincere thanks to Joanne Saksa for her gracious hospitality and
warmest gratitude to Brenda DeMay, for her unconditional love and continually
encouraging me to challenge myself.
I am most indebted to Dr. L. Michael Snyder, a true mentor throughout the years who
has taught me that anything is possible— even the Boston Red Sox can win the World
Series! Special thanks to all of the authors for their hard work and commitment,
especially Liberto Pechet, a true gentleman.
Mary A. Williamson, MT(ASCP), PhD
To my wife Barbara, and children Cathe, Lizzy, and John for their tireless

understanding and support throughout the years.
To my assistant Suzanne O’Brien for her dedication and help with the textbook.
I would also like to acknowledge Dr. Mary Williamson, for without her commitment,
dedication and hard work, we would not have met the target date for completion of
the tenth edition.
L. Michael Snyder, MD


Contributors
M. Rabie Al-Turkmani, BPharm, PhD
Assistant Professor
Department of Pathology
University of Massachusetts Medical School
Associate Director, Immunology, Immunoassay & Hematology Laboratories
UMass Memorial Medical Center
Worcester, Massachusetts
Scientific Director,
Quest Diagnostics MA, LLC
Marlborough, Massachusetts

Vishesh Chhibber
Medical Director, Transfusion Medicine
North Shore University Hospital
Hofstra North Shore-LIJ School of Medicine North Shore-LIJ Health System
Manhasset, New York

Marzena M. Galdzicka, PhD, MP(ASCP)CM , DABCC
Clinical Assistant Professor
Department of Pathology
University of Massachusetts Medical School

Shrewsbury, Massachusetts
Scientific Director,
Quest Diagnostics MA, LLC
Marlborough, Massachusetts

Edward I. Ginns, MD, PhD, DABCC
Professor of Neurology, Pathology, Pediatrics and Psychiatry
Director, Lysosomal Disorders Treatment and Research Program
University of Massachusetts Medical School
Shrewsbury, Massachusetts
Scientific Director,
Quest Diagnostics MA, LLC
Marlborough, Massachusetts

Amanda J. Jenkins, PhD
Associate Professor
Department of Pathology
University of Massachusetts Medical School
Director, Toxicology
UMass Memorial Medical Center


Worcester, Massachusetts
Scientific Director,
Quest Diagnostics MA, LLC
Marlborough, Massachusetts

Charles R. Kiefer, PhD
Associate Professor
Department of Pathology

University of Massachusetts Medical School
Director, Andrology Laboratory
Director, Clinical Assay Research
UMass Memorial Medical Center
Worcester, Massachusetts

Patricia Minehart Miron, PhD
Clinical Associate Professor of Pathology and Pediatrics
University of Massachusetts Medical School
Director, Cytogenetics
UMass Memorial Medical Center
Worcester, Massachusetts
Scientific Director,
Quest Diagnostics MA, LLC
Marlborough, Massachusetts

Michael J. Mitchell, MD
Clinical Associate Professor
Department of Pathology
University of Massachusetts Medical School
Director, Microbiology
UMass Memorial Medical Center
Worcester, Massachusetts
Scientific Director,
Quest Diagnostics MA, LLC
Marlborough, Massachusetts

Liberto Pechet, MD
Professor Emeritus
Departments of Pathology and Medicine

University of Massachusetts Medical School
Worcester, Massachusetts

Lokinendi V. Rao, PhD
Clinical Associate Professor
Department of Pathology


University of Massachusetts Medical School
Laboratory Director, UMass Memorial Clinical Laboratories
UMass Memorial Medical Center
Worcester, Massachusetts
Scientific Director,
Quest Diagnostics MA, LLC
Marlborough, Massachusetts

Craig S. Smith, MD
Assistant Professor
Department of Medicine
University of Massachusetts Medical School
Director, Cardiac Intensive Care
Division of Cardiology
UMass Memorial Medical Center
Worcester, Massachusetts

L. Michael Snyder, MD
Professor
Department of Medicine and Pathology
University of Massachusetts Medical School
UMass Memorial Medical Center

Worcester, Massachusetts
Chief Medical Officer,
Quest Diagnostics MA, LLC
Marlborough, Massachusetts

Juliana G. Szakacs, MD, MSW
Director of Pathology and Laboratory Medicine
Harvard Vanguard Medical Associates
Boston, Massachusetts

Mary A. Williamson, MT (ASCP), PhD
Vice President, Scientific Affairs & Laboratory Operations
ACM Medical Laboratory
Rochester, New York
Former Assistant Professor
Department of Pathology
University of Massachusetts Medical School
Worcester, Massachusetts

Hongbo Yu, MD, PhD
Associate Professor
Department of Pathology


University of Massachusetts Medical School
Director, Hematopathology and Hematopathology Fellowship Program
Director, Flow Cytometry Laboratory
UMass Memorial Medical Center
Worcester, Massachusetts

Tribute to Jacques Wallach

Jacques Wallach, pathologist, educator, and author of this book left us on August 10, 2010. He was
84. Forty years before that, he wrote the first edition, widely recognized as a necessary resource for
both busy house staff and seasoned clinicians alike. It was the product of his vast experience as a
clinical pathologist, his unquenchable thirst for medical knowledge, and his passion for teaching. He
devoted tireless hours of research toward updating this book seven times since then. Several
hundreds of thousands of copies have been distributed in numerous translations throughout the world.
As a resident in Internal Medicine in the mid-1980s, my first encounter with this book came in the
early hours before our daily morning report, as my fellow house officers scurried to review the
overnight admissions prior to presenting these cases to the Department Chief. The ensuing hour was
usually punctuated by moments when one or more of us incurred the Chief’s wrath for failure to
accurately appreciate the patient’s disorder or appropriately intervene. In an effort to avoid a similar
fate, each of us would keep a copy of the book in an overfilled pocket of our lab coat to review
quickly prior to this daily inquisition. Years later, I witnessed many students and house officers under
my supervision do same, often secretly racing each other to the passage contained therein that would
earn them the sought after recognition of their peers.
In the years that followed, I saw the third edition of the book become the fourth, fifth, and so on,
never really appreciating the work that Jacques put into each update. Like many of us, however, I did
appreciate the place that each update had among my collection of those clinical books, which were
always kept within easy reach and never seemed to collect any dust in my personal medical library.
When I first met Jacques, I was impressed by his dedication and commitment to medical
education. He taught pathology at Albert Einstein, Rutgers, and SUNY Downstate and consulted for
Children’s Specialized Hospital in Mountainside, South Amboy Memorial Hospital, Kings County
Hospital in Brooklyn, and for the Bronx Zoo. He also wrote Rheumatic Heart Disease (1962) and
Interpretation of Pediatric Tests (1983) as well as over 40 articles for peer review medical


journals. He was a Fellow of the American College of Physicians, the American Society of Clinical

Pathologists, the College of American Pathologists, and the New York Academy of Medicine. From
1975 to 1985, he donated his time and expertise in pathology to laboratories around the world. His
office was crammed with countless notes he made while researching, scrolled on small pieces of
paper, and filed between the pages of dozens of medical books and journals, waiting their turn to
adorn the pages of his next book. It was like he realized that clinicians and patients around the world
depended on him to unlock the keys to their own medical mysteries, and he did not take that
responsibility lightly. More recently, Jacques asked me to join his small list of distinguished
contributors and lend some assistance in my own area of expertise. To contribute in some small way
to his labor of love was truly an honor.
As the devoted teacher, nothing was more rewarding to Jacques than being able to impart the
wisdom he had worked hard to accumulate to the pupil looking for guidance. This ninth edition and
all subsequent editions, now entitled Wallach’s Interpretation of Diagnostic Tests, represent his
legacy and his ongoing gift to physicians around the world who continue to use his guidance everyday
to care for their patients. I have no doubt that nothing would have made him happier.
ANTHONY G. AUTERI, MD


Preface
In the 10th edition of Wallach’s, the authors continue to modify the content and organization based on
feedback from readers as well as attempting to keep pace with a rapidly changing health care
environment. Since the main focus of the textbook is to stress the most efficient use of clinical lab
testing, we have changed the format so that the first section will now be devoted to disease states.
Moreover, we have extended the presentation of the patient’s chief complaints and physical findings
format to additional chapters such as pulmonary, cardiac, and neurologic disease states. We have
added chapters on HLA, Transfusion Medicine, and OBGYN and updated the chapters on Molecular
Diagnostics and Cardiology.
The second section will now list the individual lab tests in alphabetical order stressing the
integration of the clinical laboratory results in the clinical decision-making process. When
appropriate, tests will include the sensitivity, specificity, and positive and negative probability.
Infectious disease assays as before are listed separately.

We have enhanced the index to make it easier for the reader to locate the subjects of interest. In
addition, we have created a robust electronic version, which will include “hypertexting” of tests
mentioned in the disease section referring back to the individual test section. This textbook does not
include references to pathophysiology or therapy. However, common pitfalls and limitations of testing
as well as identifying appropriate tests for specific clinical presentations are addressed.
As in previous editions, this textbook is geared to the primary care physician, subspecialists,
physician’s assistant, nurse practitioner, as well as medical and nursing students. The 10th edition is
not an exhaustive catalogue of disease states but a practical guide. We would appreciate continued
feedback about changes we have instituted and further comments.
L. MICHAEL SNYDER, MD
GARY LAPIDAS
MARY A. WILLIAMSON, MT (ASCP), PHD


Preface to the First Edition
Results of laboratory tests may aid in
Discovering occult disease
Preventing irreparable damage (e.g., phenylketonuria)
Early diagnosis after onset of signs or symptoms
Differential diagnosis of various possible diseases
Determining the stage of the disease
Estimating the activity of the disease
Detecting the recurrence of disease
Monitoring the effect of therapy
Genetic counseling in familial conditions
Medicolegal problems, such as paternity suits
This book is written to help the physician achieve these purposes the least amount of
Duplication of texts
Waste of patient’s money
Overtaxing of laboratory facilities and personnel

Loss of physician’s time Confusion caused by the increasing number, variety, and complexity of
tests currently available. Some of these tests may be unrequested but performed as part of
routine surveys or hospital admission multitest screening.
In order to provide quick reference and maximum availability and usefulness, this handy-sized book
features
Tabular and graphic style of concise presentation
Emphasis on serial time changes in laboratory findings in various stages of disease
Omission of rarely performed, irrelevant, esoteric, and outmoded laboratory tests
Exclusion of discussion of physiologic mechanisms, metabolic pathways, clinical features, and
nonlaboratory aspects of disease
Discussion of only the more important diseases that the physician encounters and should be able
to diagnose
This book is not
An encyclopedic compendium of clinical pathology
A technical manual
A substitute for good clinical judgment and basic knowledge of medicine
Deliberately omitted are
Technical procedures and directions
Photographs and illustrations of anatomic changes (e.g., blood cells, karyotypes, isotope scans)
Discussions of quality control
Selection of a referral laboratory
Performance of laboratory tests in the clinician’s own office
Bibliographic references, except for the most general reference texts in medicine, hematology, and
clinical pathology and for some recent references to specific conditions
The usefulness and need for a book of this style, organization, and contents have been increased by
such current trends as
The frequent lack of personal assistance, advice, and consultation in large commercial


laboratories and hospital departments of clinical pathology, which are often specialized and

fragmented as well as impersonal
Greater demand for the physician’s time
The development of many new tests
Faculty and administrators still assume that this essential area of medicine can be learned
“intuitively” as it was 20 years ago and that it therefore requires little formal training. This
attitude ignores changes in the number and variety of tests now available as well as their
increased sophistication and basic value in establishing a diagnosis.
The contents of this book are organized to answer the questions most often posed by physicians
when they require assistance from the pathologist. There is no other single adequate source of
information presented in this fashion. It appears from numerous comments I have received that this
book has succeeded in meeting the needs not only of practicing physicians and medical students but
also of pathologists, technologists, and other medical personnel. It has been adopted by many schools
of nursing and of medical technology, physician’s assistant training programs, and medical schools.
Such widespread acceptance confirms my original premise in writing this book and is most gratifying.
A perusal of the table of contents and index will quickly show the general organization of the
material by type of laboratory test or organ system or certain other categories. In order to maintain a
concise format, separate chapters have not been organized for such categories as newborn, pediatric,
and geriatric periods or for primary psychiatric or dermatologic diseases. A complete index provides
maximum access to this information.
Obviously, these data are not original but have been adapted from many sources over the years.
Only the selection, organization, manner of presentation, and emphasis are original. I have formulated
this point of view during 40 years as a clinician and pathologist, viewing with pride the important and
growing role of the laboratory but deeply regretting its inappropriate utilization.
This book was written to improve laboratory utilization by making it simpler for the physician to
select and interpret the most useful laboratory tests for his clinical problems.
J.W.


Contents
Contributors

Tribute to Jacques Wallach
Preface
Preface to the First Edition

Introduction
CHAPTER 1 FALTs: Factors Affecting Laboratory Tests
Lokinendi V. Rao

SECTION 1

DISEASE STATES

CHAPTER 2 Autoimmune Diseases
M. Rabie Al-Turkmani
CHAPTER 3 Cardiovascular Disorders
Craig S. Smith
CHAPTER 4 Central Nervous System Disorders
Juliana G. Szakacs
CHAPTER 5 Digestive Diseases
L. Michael Snyder and Michael J. Mitchell
CHAPTER 6 Endocrine Diseases
Hongbo Yu
CHAPTER 7 Genitourinary System Disorders
Charles R. Kiefer
CHAPTER 8 Gynecologic and Obstetric Disorders
Juliana G. Szakacs
CHAPTER 9 Hematologic Disorders
Liberto Pechet
CHAPTER 10 Hereditary and Genetic Diseases
Marzena M. Galdzicka, Patricia Minehart Miron, and Edward I. Ginns

CHAPTER 11 Infectious Diseases
Michael J. Mitchell
CHAPTER 12 Renal Disorders
M. Rabie Al-Turkmani
CHAPTER 13 Respiratory, Metabolic, and Acid–Base Disorders
Lokinendi V. Rao and Michael J. Mitchell


CHAPTER 14 Toxicology and Therapeutic Drug Monitoring
Amanda J. Jenkins
CHAPTER 15 Transfusion Medicine
Vishesh Chhibber

SECTION 2 LAB TESTS
CHAPTER 16 Laboratory Tests
Lokinendi V. Rao and Liberto Pechet
CHAPTER 17 Infectious Disease Assays
Michael J. Mitchell and Lokinendi V. Rao
APPENDIX

Abbreviations and Acronyms
Index


Introduction
Chapter 1

FALTs: Factors Affecting Laboratory Tests
Lokinendi V. Rao

What Causes Abnormal Test Results (Besides Disease)?
Preanalytic Errors
Physiologic Factors
Specimen Handling Factors
Analytic Errors
Diagnostic Test Values
Accuracy and Precision
Receiver Operating Characteristic (ROC) Curves
Postanalytic Errors

Reference Intervals
Performing the Right Test at the Right Time for the Right Reason

Laboratory testing is an integral part of modern medical practice. Although clinical laboratory testing
accounts for only 2.3% of annual health care costs in the United States, it plays a major role in the
clinical decisions made by physicians, nurses, and other health care providers for the overall
management of disease. More than 4,000 laboratory tests are available for clinical use, and about 500
of them are performed regularly. The number of Clinical Laboratory Improvement Amendments
(CLIA)-certified laboratories has grown to exceed more than 200,000. The laboratory medicine
workforce comprises pathologists, doctorallevel laboratory scientists, technologists, and technicians,
who play a vital role in the health care system.
The health care system is increasingly dependent on reliable clinical laboratory services;
however, as part of the overall health care system, these laboratory evaluations are prone to errors.
Laboratory medicine comprises more than just the use of chemicals and reagents for the measurement
of various analytes for clinical diagnosis purposes. Interference by both endogenous and exogenous
substances is a common problem for the test analysis. These substances play a significant role in the
proper interpretation of results, and such interference is adverse to patient care and adds to the cost of
health care. It would be an oversimplification to conclude that each variable will always produce a

specific effect; it depends on the person, the duration of exposure to that variable, and the time
between initial stress, the sample collection, and the degree of exposure. Awareness that many factors
occurring outside the laboratory in and around the patient may affect the test result before the sample
reaches the laboratory or even before the sample is collected is very important. These factors can be
minimized when the clinician takes a good history and when there is a good communication of such
information between the laboratory and the physician.

WHAT CAUSES ABNORMAL TEST RESULTS (BESIDES
DISEASE)?
The total testing process defines the preanalytic, analytic, and postanalytic phases of laboratory
testing and serves as the basis for designing and implementing interventions, restrictions, or limits
that can reduce or remove the likelihood of errors. Over the last several years, there has been a
remarkable decrease in error rates, especially analytic errors. Evidence from recent studies
demonstrates that a large percentage of laboratory errors occur in preanalytic and postanalytic steps.
Errors in the preanalytic (61.9%) and postanalytic (23.1%) processes occurred much more frequently
than occurrences of analytic errors (15%). About one fourth of these can have consequences to the
patient either in delay of the test result or life threatening.

PREANALYTIC ERRORS
Preanalytic factors act on both the patient and the specimen before analyses. These factors may be
divided further into those acting in vivo (biologic or physiologic) and those acting in vitro (specimen
handling and interference factors).

PHYSIOLOGIC FACTORS
Some physiologic factors are beyond our control. They include age, sex, and race, and so on, and can
be managed by placing appropriate reference limits. Others factors such as diet, starvation, exercise,
posture, diurnal and seasonal variations, menstrual cycle, and pregnancy must be considered in the
interpretation of the test results. Age has noticeable effect on some test results and the need for
establishing appropriate reference intervals. In newborns, the composition of blood is affected by the
maturity of the infant at birth. At birth, RBC and hemoglobin values are higher than adults due to low

levels of oxygen in the uterus. They continue to decrease and level out to adult values about the age of
15. Adult values are usually taken as the reference for comparison with those of the young and the
elderly. The concentration of most test constituents remains constant between puberty and menopause
in women and between puberty and middle age in men. The plasma concentrations of many
constituents increase in women after menopause. Hormone levels are affected by aging. However,
changes in concentrations are much less pronounced than an endocrine organ’s response to stimuli.
Until puberty, there are few differences in laboratory data between boys and girls. After puberty, the
characteristic changes in the levels of sex hormones become apparent.
In addition to the commonly known hormonal changes during the menstrual cycle, there is a
preovulatory increase in the concentrations of aldosterone and renin. Coincident with the ovulation,


serum cholesterol levels are lower than at any other phase of the menstrual cycle. In pregnancy, a
dilutional effect is observed due to the increase in mean plasma volume, which in turn causes
hemodilution. Normal pregnancy is characterized by major physiologic adaptations that alter maternal
blood chemistry and hematology laboratory values. In addition, there are time-related fluctuations in
the levels of certain analytes. Many analytes—such as cortisol, thyrotropin (TSH), growth hormone,
potassium, glucose, iron, and proinflammatory cytokines—exhibit diurnal variation. Hormones such
as luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone released in short
bursts lasting barely 2 minutes make accurate measurements problematic. Seasonal changes also
affect certain analytes like vitamin D (higher during summer), cholesterol, and thyroid hormones
(higher during winter). Changes in the levels of some of the constituents in blood occur when
measured at sea level as opposed to measurement at a higher altitude. Hematocrit, hemoglobin, and
C-reactive protein (CRP) can be higher at high altitude. Levels of plasma renin, transferrin, urinary
creatinine, creatinine clearance, and estriol decrease with increasing altitude.
The dietary effect of laboratory test results is complex and simply cannot be separated into the
categories of “fasting” and “nonfasting” status of the patient. A significant variation in some routine
tests after a regular meal showing that fasting time needs to be carefully considered when performing
tests to prevent spurious results. Clinically significant differences are observed within 1–4 hours for
triglycerides, albumin, ALT, calcium, iron, LDH, phosphorus, magnesium, lymphocytes, RBC,

hemoglobin, hematocrit, etc. The type of diet (high fat, low fat, vegetarian, malnutrition), length of
time since last meal, and test-specific dietary concerns can affect some tests. Consumption of
caffeine, bran, serotonin (consumption of fruits and vegetables such as bananas, avocados, and
onions), herbal preparations (e.g., aloe vera, Chinese rhubarb, senna, quinine, and quinidine),
recreational drug use, ethanol, and smoking can induce both short- and long-term effects that alter the
results of several analytes. Differentiations of the effects of race from those of socioeconomic
conditions are difficult. Carbohydrate and lipid metabolism differ in blacks and whites. Glucose
tolerance is less in blacks, Polynesians, and Native Americans in comparison to whites.
Physical stress and mental stress influence the concentrations of many plasma constituents,
including cortisol, aldosterone, prolactin, TSH, aldosterone, cholesterol, glucose, insulin, and lactate.
With blindness, the normal stimulation of the hypothalamic–pituitary axis is reduced. Consequently,
certain features of hypopituitarism and hypoadrenalism may be observed. In some blind individuals,
the normal diurnal variations of cortisol may persist; in others, it does not. Fever provokes many
hormonal responses as does shock and trauma. The stress of surgery has been shown to reduce the
serum triiodothyronine (T3) levels by 50% in patients without thyroid disease.
Transfusions and infusions can also significantly affect the concentration of certain laboratory
values. For persons receiving an infusion, blood should not be obtained proximal to the infusion site.
Blood should be obtained from the opposite arm. A minimum of 8 hours must elapse before blood is
obtained from a subject who has received fat emulsion. For patients receiving blood transfusions, the
extent of hemolysis and with it increased levels of potassium, lactate dehydrogenase (LDH), and free
hemoglobin are released progressively to the age of the transfused blood.
Exercise such as running up and down several flights of stairs or strenuous activity such as
working out in a gymnasium or marathon running the night before the specimen collection can affect
the results obtained for several analytes. To minimize preanalytic variables introduced by exercise,
subjects should be instructed to refrain from strenuous activity on the night before testing and not to
exert themselves by walking a long distance, running, or climbing stairs before blood specimen
collection. In addition, the muscle damage associated with trauma of surgery will increase the serum


activity of enzymes originating in skeletal muscles, and this activity may persist for several days.

The plasma and extracellular volumes decrease within a few days of the start of bed rest. With
prolonged bed rest, fluid retention occurs and plasma protein and albumin levels may be decreased
by an average of 0.5 and 0.3 g/dL, respectively. As a result, concentrations of bound protein are also
reduced. Changes in posture during blood sampling can affect the concentrations of several analytes
measured in serum or plasma. Change in posture from a supine to an erect or sitting position can
result in a shift in body water from intravascular to interstitial compartments. As a result, the
concentrations of larger molecules that are not filterable are increased. These effects are accentuated
in patients with a tendency for edema, such as in cardiovascular insufficiency and cirrhosis of the
liver.

SPECIMEN HANDLING FACTORS
Among controllable preanalytic variables, specimen collection is most critical. Unacceptable
specimen collection due to misidentification, insufficient volume to perform test, incorrect whole
blood-to-anticoagulant ratio, and specimen quality (hemolysis, clots, contaminated, collected in
wrong container) accounts for the majority of preanalytic errors. Hemolysis, lipemia, and icteric
samples have variable effects on assays and depend upon testing method and analyte. The time and
temperature for storage of the specimen and the processing steps in the preparation of serum or
plasma or cell separation can introduce preanalytic variables.
Pneumatic tube systems of various lengths are routinely used in many hospitals to transport blood
collection tubes to the testing laboratory. Significant differences between plasma but not serum levels
of LDH are observed when blood collection tubes are transported through pneumatic tube systems.
The application of a tourniquet, by reducing the pressure below the systolic pressure, maintains the
effective filtration pressure within the capillaries. As a result, small molecules and fluid are
transferred from the intravasal space to the interstitium. Application of tourniquet for longer than 1
minute can result in hemoconcentration of large molecules that are unable to penetrate the capillary
wall. To minimize the preanalytic effects of tourniquet application time, the tourniquet should be
released as soon as the needle enters the vein. Avoidance of excessive fist clenching during
phlebotomy and maintaining tourniquet application time to no more than 1 minute can minimize
preanalytic errors.
Various salts of heparin, ethylenediaminetetraacetic acid (EDTA), and sodium citrate are used

widely in the clinical laboratory. Heparin is the preferred anticoagulant for blood specimens for
electrolyte levels and other routine chemistry tests. Obvious differences in the results of certain
analytes between serum and heparinized plasma are related to the consumption of fibrinogen and the
lysis of cellular elements during the process of clotting. EDTA is the commonly used anticoagulant for
routine hematologic determinations. It functions as anticoagulant by chelating calcium ions, which are
required for the clotting process. Citrate has been used as an anticoagulant for collection of blood
specimens intended for global coagulation tests such as prothrombin time (PT) and partial
thromboplastin time (PTT). A laboratory that has been using one of the concentrations (3.2% or
3.8%) to perform PT determination for patients receiving oral anticoagulant therapy should not
interchange the formulations. Doing so will affect the international normalized ratios (INRs) that are
used to report the results of PT. Sodium fluoride and lithium iodoacetate have been used alone or in
combination with anticoagulants such as potassium oxalate, EDTA, citrate, or lithium heparin for
blood collection. In the absence of glycolytic inhibitors, a decrease in the glucose level of as much as


24% can occur in 1 hour after blood collection in neonates, in contrast to a 5% decrease in healthy
individuals when specimen is stored at room temperature. The anticoagulant-to-blood ratio is critical
for some laboratory tests. In general, collecting of blood specimens to less than nominal volume
increases the effective molarity of the anticoagulant and induces osmotic changes affecting cell
morphologic features. Furthermore, the binding of analytes such as ionic calcium or magnesium to
heparin can be enhanced when the effective concentration of unfractionated heparin increased beyond
the normal 14.3 U/mL of blood. In addition, stability of various analytes are significantly reduced in
plasma (Lithium Heparin) compared to serum tubes when plasma is stored, but not separated from the
gel after centrifugation.
Virtually, all drugs may affect the results of clinical laboratory tests that includes both in vivo
(pharmacologic) and in vitro (interferences and methodologic) effects. The problem of drug
interference is complex, and physicians are generally aware of main therapeutic effects of drug, but
many secondary effects are ignored. Some of the examples are increase in liver enzymes with
Dilantin and barbiturates, increase in fibrinogen, transferrin, amylase, etc. following oral
contraceptives and contrast agents (gadolinium) decreasing total calcium levels.

In coagulation, testing knowledge or access to the patient history may be necessary, as many
medications such as anticoagulant therapies (warfarin, heparin, and direct thrombin inhibitors), blood
product, and component transfusion and coagulation factor replacement therapies all impact
coagulation test results. Over-the-counter drugs (aspirin) have prolonged effect on platelet function
studies. In addition, the patient’s physiologic state plays a role.
The quality of the specimens submitted to the microbiology laboratory is critical for optimal
specimen evaluation. The general techniques of specimen collection and handling that have been
established both to maximize the yield of organisms and isolate relevant pathogens from specimens
obtained from different body sites should be reviewed with clinical laboratory prior to obtaining the
specimen. In addition, valid interpretation of the results of culture can be achieved only if the
specimen obtained is appropriate for processing. As a result, care must be taken to collect only those
specimens that may yield pathogens, rather than colonizing flora or contaminants. Specific rules for
the collection of material vary, depending on the source of the specimen, but several general
principles apply. Prompt transport of specimens to the microbiology laboratory is essential to
optimize the yield of cultures and the interpretation of results. Delays in processing may result in the
overgrowth of some microorganisms or the death of more fastidious ones. Samples for bacterial
culture should ideally arrive in the microbiology laboratory within 1 to 2 hours of collection. If a
delay is unavoidable, most specimens (with the exception of blood, cerebrospinal fluid, joint fluid,
and cultures for Neisseria gonorrhoeae) should be refrigerated until transported.

ANALYTIC ERRORS
Clinical laboratories have long focused their attention on quality control methods and quality
assessment programs dealing with analytic aspects of testing. Total analytic error (or measurement
error) refers to assay errors from all sources arising from the data collection experiment. Some error
is expected, because not all components of measuring are the same. There are four major types of
experimental error: random (not predictable), systematic (one direction), total (random and
systematic), and idiosyncratic (nonmethodologic).
Errors due to analytic problems have been significantly reduced over time, but there is evidence

that, particularly for immunoassays, interference may have a serious impact on patients. Paraproteins
can interfere in chemical measurements when they form precipitates during the testing procedure.
Heterophilic antibodies are human antibodies that can bind animal antibodies. They can cause
problems in immunoassays, particularly immunometric assays, where they can form a bridge between
the capture and detection antibodies, leading to false-positive results in the absence of analyte or if
analyte is also present, a false increase in measured concentrations. Very rarely, heterophilic
antibodies can also lead to false-negative or falsely low results.
Very high hormone levels can interfere with immunoassay systems, resulting in falsely low analyte
determinations. This is attributable to the “hook effect,” which describes the inhibition of immune
complex formation by excess antigen concentration. There are proteins that are well known to form
aggregates with immunoglobulins or high molecular weight proteins. Clinically relevant proteins that
can have “macro” forms—including amylase, creatinine kinase, LDH, and prolactin—can elevate the
results when using certain laboratory tests, yet the patient lacks clinical disease related to elevated
analyte concentration.
Immunoassay interference is not analyte specific and is variable with respect to time. In some
patients, this interference can lost for a long time and in some for only a short time. This interference
affects lots of assays but not all of them. In addition, a different manufacturer’s test kits have different
cross-reactions with interference compounds, and the test results vary from lab to lab.
Incorrect results can also occur as a result of a large number of biologically common phenomena
causing analytic variation. These include cold agglutinins, rouleaux, osmotic matrix effects, platelet
agglutination, giant platelets, unlysed erythrocytes, nucleated erythrocytes, megakaryocytes, red cell
inclusions, cryoproteins, circulating mucin, leukocytosis, in vitro hemolysis, extreme microcytosis,
bilirubinemia, lipemia, and so on.

DIAGNOSTIC TEST VALUES
Before a method is used routinely, method evaluation protocols must ensure that the measurement
procedure meets defined criteria, for example, the accuracy, precision, and stability required in
meeting the laboratory’s patient population needs. Four indicators are most commonly used to
determine the reliability of a clinical laboratory test. Two of these, accuracy and precision, reflect
how well the test method performs day to day in a laboratory. The other two, sensitivity and

specificity, deal with how well the test is able to distinguish disease from the absence of disease.
The accuracy and precision of each test method are established and are frequently monitored by
the clinical laboratory. Sensitivity and specificity data are determined by research studies and
clinical trials. Although each test has its own performance measures and appropriate uses, laboratory
tests are designed to be as precise, accurate, specific, and sensitive as possible.

ACCURACY AND PRECISION
“Accuracy” (trueness) refers to the ability of the test to actually measure what it claims to measure
and is defined as the proportion of all test results (both positive and negative) that are correct.
Precision (repeatability) refers to the ability of the test to reproduce the same result when repeated
on the same patient or sample. The two concepts are related, but different. For example, a test could
be precise but not accurate if on three occasions it produced roughly the same result but that result


differed greatly from the actual value determined by a reference standard.
Sensitivity is defined as the ability of the test to identify correctly those who have the disease. It
is the number of subjects with a positive test who have the disease divided by all subjects who have
the disease. A test with high sensitivity has few false-negative results. Specificity is defined as the
ability of the test to identify correctly those who do not have the disease. It is the number of subjects
who have a negative test and do not have the disease divided by all subjects who do not have the
disease. A test with high specificity has few false-positive results. Sensitivity and specificity are
most useful when assessing a test used to screen a free-living population. These test characteristics
are also interdependent (Figure 1-1): an increase in sensitivity is accompanied by a decrease in
specificity and vice versa.

Figure 1–1 Sensitivity, specificity, and predictive values in laboratory testing. NPV, negative predictive value; PPV, positive
predictive value.

Predictive values are important for assessing how useful a test will be in the clinical setting at the
individual patient level. The positive predictive value (PPV) is the probability of disease in a patient

with a positive test. Conversely, the negative predictive value (NPV) is the probability that the
patient does not have disease if he has a negative test result.
PPV and sensitivity of tests are complementary in their examination of true positives. Given that
the test is positive, PPV is the probability that the disease is present, in contrast to sensitivity, which
is given that the disease is present, the probability that test is positive. Likewise, NPV and specificity
are complementary in their examination of true negatives. Given that the test is negative, NPV is the
probability that the disease is absent. This is in contrast to specificity, which is given that the disease
is absent, the probability that test is negative (see Figure 1-1 for more information). Predictive values
depend on the prevalence of a disease in a population. A test with a given sensitivity and specificity
can have different predictive values in different patient populations. If the test is used in a population
with high disease prevalence, it will have a high PPV; the same test will have a low PPV when used
in a population with low disease prevalence.
Likelihood ratios (LRs) are another way of assessing the accuracy of a test in the clinical setting.
They are also independent of disease prevalence. LR indicates how much a given diagnostic test
result will raise or lower the odds of having a disease relative to the probability of the disease. Each
test is characterized by two LRs: positive LR (PLR) and negative LR (NLR). PLR tells us the odds of


the disease if the test result is positive, and NLR tells the odds of disease if the test result is negative.

An LR >1 increases the odds that the person has the target disease, and the higher the LR, the greater
this increase in odds. Conversely, an LR ratio <1 diminishes the odds that the patient has the target
disease.

RECEIVER OPERATING CHARACTERISTIC (ROC) CURVES
ROC curves allow one to identify the cutoff value that minimizes both false positives and false
negatives. An ROC curve plots sensitivity on the y axis and 1 − specificity on the x axis. Applying a
variety of cutoff values to the same reference population allows one to generate the curve. The perfect
test would have a cutoff value that allowed an exact split of diseased and nondiseased populations
(i.e., a cutoff that gave both 100% sensitivity and 100% specificity). It would plot as a right angle

with the fulcrum in the far upper left corner (x = 0, y = 1). This case, however, is very rare. For most
cases, as one moves from the left to right on the ROC curve, the sensitivity increases and the
specificity decreases.
Calculation of the area under the ROC curve allows comparison of different tests. A perfect test
has an area under the curve (AUC) equal to 1. Therefore, the closer the AUC is to 1, the better the
test. Similarly, if one wants to know the cutoff value for a test that minimizes both false positives and
false negatives (and hence maximizes both sensitivity and specificity), one would select the point on
the ROC curve closest to the far upper left corner (x = 0, y = 1).
However, finding the right balance between optimal sensitivity and specificity may not involve
simultaneously minimizing false positives and false negatives in all situations. For example, when
screening for a deadly disease that is curable, it may be desirable to accept more false positives
(lower specificity) in return for fewer false negatives (higher sensitivity). ROC curves allow a more
thorough evaluation of a test and potential cutoff values but are not the ultimate arbiters of how to set
sensitivity and specificity.

POSTANALYTIC ERRORS
Approximately 70–80% of the patient chart or medical record is composed of laboratory test results.
Postanalytic errors are dependent on the design and development of those processes and procedures
that will ensure correct and timely notification of these test results to the patient’s medical record
with right reference range and appropriate interpretation of the test result. Manual and telephone
reporting should be discouraged as this reporting is subject to transcription errors at the receiver end.
The introduction of a hospitalized computer order entry system has eliminated some errors, but it has
not eliminated the risk of mismatching the patients.

REFERENCE INTERVALS