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 = [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