Case report: Salicylate intoxication can present with a normal anion gap metabolic acidosis depending on method used for measuring chloride.

Severe salicylate intoxication usually presents with a high anion gap metabolic acidosis. We describe a patient with severe salicylate intoxication who presented with a surprisingly normal anion gap metabolic acidosis. Initial salicylate level was 594 mg/L (therapeutic range 50-300 mg/L). In this case, the anion gap was normal due to a falsely elevated chloride concentration measured using a direct ion-selective electrode (ISE; ABL90-flex). Since earlier case reports have shown that salicylate ions can interfere with chloride measurement using different ISEs, available samples were reanalysed using an indirect ISE (Roche Cobas 8000), in which salicylate levels up to 1000 mg/L were found to cause no significant interference. With this method, chloride concentration was found to be 115 instead of 122 mmol/L, leading to the expected elevated anion gap. We performed a spike experiment to investigate the impact of different salicylate levels and bicarbonate concentrations on the measured chloride concentration for both methods. This experiment showed that the difference between chloride concentrations was mainly explained by interference with bicarbonate. It is important for clinicians to be aware of this possible interference, since a high anion gap metabolic acidosis can be a clue to suspect salicylate poisoning and early recognition and appropriate treatment is important. The patient was successfully treated with haemodialysis and no rebound toxicity was observed.