Negative anion gap metabolic acidosis in salicylate overdose--a zebra!

Salicylate poisoning classically results in an increased anion gap metabolic acidosis. We discuss a case of normal anion gap metabolic acidosis despite elevated serum salicylate concentration. This diagnostic dilemma stemmed from aberrant reading of salicylate ions by analyzer electrodes as chloride ions leading to falsely negative anion gap. On review, this phenomenon is found to be possible with a number of commonly used analyzers. In emergency department settings, high level of clinical suspicion for salicylate poisoning should be maintained, and metabolic acidosis with normal anion gap should not be used to rule out salicylate overdose. This can prevent significant avoidable morbidity and mortality.