Severe salicylate poisoning can cause metabolic acidosis from an accumulation of salicylic acid, lactic acid, and ketone bodies. A high anion gap acidosis is therefore the typical metabolic abnormality seen. A case series illustrates salicylate poisoning presenting with a normal gap (hyperchloraemic) acidosis – one patient had a chloride of 111 mmol/l and the other 123 mmol/l. This can occur when some analysers falsely read an elevated chloride in the presence of high concentrations of salicylate.

Severe salicylate poisoning is classically associated with an anion gap metabolic acidosis. However, high serum salicylate levels can cause false increase of laboratory chloride results on some analyzers. We present 2 cases of life-threatening salicylate poisoning with an apparently normal anion gap caused by an important laboratory interference. These cases highlight that the diagnosis of severe salicylism must be considered in all patients presenting with metabolic acidosis, even in the absence of an increased anion gap.

Falsely Normal Anion Gap in Severe Salicylate Poisoning Caused by Laboratory Interference
Ann Emerg Med. 2011 Sep;58(3):280-1