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Laboratory Evaluation
Laboratory studies may be helpful in confirming diagnostic impressions or in
demonstrating toxicant-induced metabolic aberrations. However, there is no “tox
panel” that is uniformly helpful or necessary. Most poisonings can be managed
appropriately without extensive laboratory studies, and in particular, the reflex
ordering of rapid overdose toxicology screens is rarely helpful in acute patient
management. They may have important, nonemergent roles (e.g., in resolving
medicolegal issues or considering drug-induced causes of behavioral changes in a
psychiatric patient). In toddlers with a known or strongly suspected specific
ingestion, rapid drug screens are rarely indicated. In the adolescent intentional
overdose patient who is not critically ill or who does not have a particularly
puzzling clinical picture, the drug screen is rarely helpful, although adolescents
may ingest multiple drugs and may not be truthful. Therefore, some authors
recommend serum levels of acetaminophen and salicylates, two of the most
common treatable co-ingestants. The comprehensive urine drug screen may rarely
be useful for seriously ill patients with an occult ingestion, or for the intentional
overdose adolescent patient whose clinical picture does not fit with the stated
history. Often more helpful is the critical interpretation of routine measurements
of serum chemistries, blood gas analysis, and osmolality in patients with altered
mental status. The presence of hypoglycemia or aberrations of serum electrolytes
may provide crucial information about the poisoned patient. In certain
circumstances, tests of liver or renal function, urinalysis, creatine phosphokinase
levels, and other select tests may be useful. Metabolic acidosis with a high anion
gap is found in many clinical syndromes and toxidromes, reflected by the oftencited mnemonic MUDPILES, for m ethanol and m etformin; u remia; d iabetic
and other ketoacidoses; p araldehyde and p aracetamol (acetaminophen); i
soniazid (INH), i ron, i nborn errors of metabolism and massive i buprofen; l actic
acidosis (seen with hypoxia, shock, carbon monoxide, cyanide, and many drugs
that cause compromised cardiorespiratory status or prolonged seizures); e thylene
glycol; and s alicylates or s eizures. Differences between calculated and measured
serum osmolarity (calculated = 2 [serum Na mEq per L] + blood urea nitrogen
[BUN] mg per dL ÷ 2.8 + glucose mg per dL ÷ 18; with normal osmolarity ∼290

mOsm/kg) may suggest intoxication with ethanol, isopropanol, or more rarely in
pediatric patients, methanol or ethylene glycol. Do not use blood collection tubes
containing ethylenediaminetetraacetic acid (EDTA) because the osmolal gap will
be falsely elevated.