Clinical assessment of an enzyme immunoassay (EMIT) for measurement of serum salicylate.

Salicylic acid concentrations in serum were compared using a homogenous enzyme immunoassay (EMIT) and an automated colorimetric analysis (ACA) technique. Analysis of samples showed similar within-day and day-to-day coefficients of variation (CV): 1.3% and 4.6% by EMIT and 1.0% and 2.6% by ACA, respectively. Quantification of serum containing added salicylate and serum from patients receiving salicylate therapy showed a slight positive bias towards the ACA method over the range of 0-600 mg/l. No significant difference in reliability was found between the two methods. The EMIT assay showed no interference from other antiflammatory drugs being taken by patients who were not taking salicylates. If decisions to alter salicylate dosage are made with due regard to the drug's saturation kinetics, measurements using either EMIT or ACA should allow the clinician to titrate patients' serum concentrations accurately within the narrow therapeutic range.