Intrepretation of laboratory tests

Intrepretation of Laboratory
Tests
Joseph S. Bertino Jr., Pharm.D.
Bertino Consulting

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Goals and Objectives
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Review common laboratory tests

– Chemistry
– Hematology
– Urinalysis
– Cerebral Spinal Fluid
– Microbiology and Serology

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Discuss how pharmacists can use information to assist in drug therapy

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Specimen Types
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Serum: the fluid from blood after blood cells and clot are removed
Plasma: fluid from blood centrifuged with anticoagulants
Erythrocytes: red blood cells
Leukocytes: white blood cells
Urine: Random or “clean catch” (for microbiology)
Feces
Cerebral Spinal Fluid
Joint Fluid

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Normal values are specific to
a laboratory, I give general
normal ranges in this lecture

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Chemistry

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Sodium (Na )
+

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Measures amount of serum sodium

– Major cation in the blood
– Balance depends on intake and renal excretion

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Normal: 136 – 146 mmol/L
Critical values: < 120 or > 160 mmol/L
↑ Sodium (hypernatremia): ↑ Na+ intake, ↓ Na+ loss, Excessive free water loss
↓ Sodium (hyponatremia): ↓ Na+ intake, ↑ Na+ loss, ↑ free water intake

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Correction of Hypernatremia
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Acute hypernatremia

– Decrease serum sodium by 1 mmol/L each
hour
– If patient has normal blood pressure use
0.45% NaCl IV infusion
– If patient has low blood pressure use 0.9%
NaCl until BP is normal, then 0.45% NaCl IV
infusion
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Chronic hypernatremia

– Decrease serum sodium slowly (0.5 mmol/L
each hour) to avoid cerebral edema
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Correction of Hyponatremia
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Increase serum sodium by 0.5 mmol/L each hour and 10 mmol/L in 24 hours or 18 mmol/L

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Restrict fluid

in 48 hours

3% NaCl should only be used for moderate to severe hyponatremia (very symptomatic)

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Use of 3% NaCl for Hyponatremia
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Choose desired correction rate of serum sodium (Example: correct at

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Multiply patient’s weight X desired correction rate and infuse as ml/h of

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For example in a 60 kg patient: 60 kg X 1.0 mmol/L/h = 60 ml/h infusion of

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Correct at no more than 1.0 mmol/hr

1.0 mmol/L/h)
3% NaCl intravenously
3% NaCl

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Potassium (K )
+

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Measures serum potassium level

– Majority of potassium is in cells
(intracellular), not in serum (extracellular)
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Normal potassium value: 3.4 – 5.2 mmol/L

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↓ potassium (hypokalemia): insufficient K+ intake, burns, hyperaldosteronism,
Cushing syndrome, renal tubular acidosis, alkalosis, renal artery stenosis

Critical potassium value: < 2.5 or > 6.5 mmol/L

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Potassium
– ↑ potassium (hyperkalemia): excessive K+ intake,

acidosis, acute/chronic renal failure, Addison
disease, hypoaldosteronism, infection,
dehydration
– if a specimen is hemolyzed (such as by traumatic venipuncture or drawing blood with a
needle that is too small) potassium value may be “falsely” high

– There are high concentrations of K in red blood
cells. If RBCs are broken during phlebotomy, K is
released into the serum resulting in elevated
measured K levels (falsely elevated)

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Correction of Hypokalemia
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1 mmol/L drop in K+ = 200-400 mmol K in body
If K+ = 2.5-3.5 mmol/L with minor symptoms treat with oral potassium
If K= < 2.5 mmol/L treat with IV potassium
IV dose 10 mmol/hr, can also give oral K+ at the same time
For higher amounts of K+ IV, need to use a central venous line
Check Mg+2, if serum Mg+2 low, replace Mg also

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Correction of Hyperkalemia
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Stop all potassium and diuretics that prevent renal excretion of potassium

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Inhaled beta 2 agonists (salbutamol 20 mg inhalation)

Insulin + glucose + sodium bicarbonate IV
Furosemide IV
Sodium polystyrene sulfonate by mouth to bind K+ in bowel (do not mix
with sorbitol)

Calcium IV to reduce cardiac effects
Dialysis

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Chloride (Cl )
-

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Measures serum chloride level

– Major anion in extracellular space
– Helps maintain electrical neutrality;
Chloride follows sodium
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Normal: 98 – 108 mmol/L
Critical: < 80 or > 115 mmol/L

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Chloride
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↑ (Hyperchloremia): dehydration, metabolic acidosis, renal tubular acidosis,
Cushing syndrome, renal dysfunction, respiratory alkalosis,
hyperparathyroidism

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↓ (Hypochloremia): overhydration, SIADH, CHF, chronic respiratory acidosis,

metabolic alkalosis, Addison disease, hyperaldosteronism,
vomiting/prolonged gastric suction, hypokalemia

Isolated chloride changes are very rare

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Bicarbonate (HCO3 )
-

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Measures CO (carbon dioxide) content of blood
2

– Major anion important for acid-base balance
– Regulated by the kidneys
– Used to evaluate the pH status of patient

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Normal range: 22 – 32 mmol/L

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↑ HCO3-: severe vomiting, high-volume gastric suction, hyperaldosteronism, COPD,
metabolic alkalosis

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↓ HCO3-: chronic diarrhea, chronic loop diuretic use, renal failure, DKA, starvation,
metabolic acidosis, shock

Critical range: < 6 mmol/L

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Bicarbonate (HCO3 )
-

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Bicarbonate replaced with either sodium or potassium cation

– Sodium Bicarbonate
– Sodium Acetate
– Potassium Acetate

1 molecule acetate converted to 1 molecule bicarbonate

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Anion Gap (AG)

 The body must maintain equal numbers of cations (+) and anions(-)
 The AG measures the excess anions in the blood, a measure of excess acid
 AG = Na – Cl – HCO3 (normal AG =12 ± 2)
 AG corrected = AG + 2.5 [4 – albumin]
 If serum albumin is <4 correct AG
 Anion Gap indicates acidosis in a patient

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Glucose
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Direct measure of blood glucose

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↑ Glucose (hyperglycemia): Diabetes, acute stress response, Cushing syndrome,
pheochromocytoma, chronic renal failure, acute pancreatitis, acromegaly, corticosteroid
therapy

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↓ Glucose (hypoglycemia): insulinoma, hypothyroidism, hypopituitarism, Addison disease,
severe liver disease, insulin overdose, starvation

Normal values: 3.8 – 6.7 mmol/L

Critical: < 2.2 and > 22.2 mmol/L

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Diagnosing Diabetes
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The criteria for the diagnosis of diabetes:

– Fasting Plasma Glucose ≥7 mmol/L
– 2 hour Post-Prandial (eating) Glucose ≥11.1 mmol/L
– Random Plasma Glucose >11.1 mmol/L in the presence of
symptoms (increase urine, thirst, hunger)
– Any one of these tests should be repeated to confirm diagnosis

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Blood Urea Nitrogen (BUN)
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Measures urea nitrogen in blood

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Normal: 2.1 -7.5 mmol/L

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↑ BUN: prerenal causes (dehydration or drugs), renal disease

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↓ BUN: liver failure, overhydration due to SIADH, pregnancy, nephrotic syndrome

– Urea nitrogen is end product of protein metabolism
(produced in liver)
– BUN is an indirect measure of renal function
– BUN is a poor measure of liver function
– BUN is usually interpreted along with serum creatinine (less
accurate than creatinine for measuring renal disease)

Critical: > 35.7 mmol/L

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Creatinine (Cr)
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Measures serum creatinine

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Normal Values: 35 – 106 umol/L

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↑ Cr: diseases affecting renal function, rhabdomyolysis, acromegaly

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↓ Cr: decreased muscle mass, corticosteroids

– Catabolic product of creatine phosphate (from skeletal
muscle)
– Creatinine is excreted entirely by kidneys → direct measure
of renal function
– Minimally affected by liver function
– Elevation of creatinine occurs slower than BUN

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Calcium
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The total serum calcium is a measure of the total of:

– Free (ionized) calcium
– Protein bound (bound to albumin) calcium

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Therefore, the total serum calcium level is affected by changes in serum
albumin

– The total serum calcium level decreases by
approximately 0.2 mmol/L for every 1gram
decrease in the serum albumin level.

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Calcium (Ca )
2+

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Normal Values:

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Critical Values: Total Ca< 1.5 or > 3.25 mmol/L, Ionized Ca < 0.55 or > 1.75 mmol/L

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↑ Ca (hypercalcemia): hyperparathyroidism, bone cancer, Paget disease of bone, prolonged
immobilization, milk-alkali syndrome, vitamin D intoxication, hyperthyroidism

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↓ Ca (hypocalcemia): hypoparathyroidism, renal failure, rickets, vitamin D deficiency,

osteomalacia, pancreatitis, alkalosis, malabsorption, fat embolism, hypomagnesemia

– Total Ca= 2.1 – 2.6 mmol/L
– Ionized Ca = 1.12 – 1.4 mmol/L

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Treatment of Calcium Disorders
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Hypercalcemia:

– Restrict calcium intake
– Restrict vitamin D intake
– IV fluids and diuretics (if severe)

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Hypocalcemia:

– Oral calcium if mild
– IV calcium if severe (tetany), 100-200 mg IV calcium gluconate
infused over 5-10 minutes

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