Salicylate (Blood)

Diagnostic Use

For detailed information on salicylate overdose, refer to toxinz Salicylate

Serum levels should be used along with considerations of severity of presenting symptoms, degree of acid–base disorders and overall clinical condition of the patient. Overreliance on serum salicylate concentrations can lead to underestimating severity of salicylate poisoning and delay of appropriate therapy, potentially contributing to worse outcomes.

In the setting of suspected acute salicylate poisoning, a salicylate level should be measured on presentation. It should then be measured every 2-4 hours to identify a peak and downward trend. This may not occur for 12 or more hours following ingestion of enteric or sustained release formulations, or ingestion of a very large numbers of tablets, or if a pharmacobezoar has formed.

If the patient is asymptomatic and the serum salicylate peak is less than 2.2 mmol/L, the patient may be discharged into the care of a reliable observer with instructions to return should signs or symptoms develop, including: nausea, vomiting, tinnitus, or sweating. Levels between 3.6-5.1mmol/L indicate severe intoxication which can be associated with fever, sweating, listlessness, and incoordination. At >5.4mmol/L, patients are at risk for hallucinations, seizures, cerebral oedema, coma, non-cardiogenic pulmonary oedema and cardiovascular collapse.

In chronic salicylate toxicity, serum concentrations alone does not fully reflect the severity of poisoning, and should be interpreted in the context of the patient’s clinical signs and symptoms and investigations, particularly blood gas analysis. Chronic poisoning is generally more severe than acute intoxication at a given serum salicylate concentration; children and the elderly are particularly vulnerable. Thresholds for interventions including urinary alkalinization and haemodialysis should therefore be lower for cases of chronic toxicity.

Reference Intervals

• Therapeutic range for anti-inflammatory use: <2.2 mmol/L
• Average single analgesic-antipyretic dose peak concentration (adults/children): usually <0.4mmol/L
• Moderate to severe toxicity: > 3.2 mmol/L
• For more guidance see toxinz Salicylate