Objective: Ferric chloride (FC) and Trinder reagent (TR) have both been used to identify salicylates (ASA) in the urine of patients presenting with possible drug overdose. The authors sought to compare the sensitivities and specificities of these two reagents in detecting ASA in the urine of patients presenting to an emergency department (ED) with suspected drug overdose.
Methods: Patients were eligible for inclusion in this study if they presented to the ED with either suspected overdose or unexplained metabolic acidosis. One milliliter of the patient's urine was added to 1 mL of each of the two reagents. A positive test was defined as any darkening of the color of the reagent. Each patient had a quantitative serum ASA measured.
Results: Twenty of 180 patients (11%) had quantitative serum ASA levels above 5 mg/dL. Both reagents were 100% sensitive in identifying these patients. The specificity of FC was 71% compared with 73% for TR. The two reagents gave similar results in 91% of cases.
Conclusion: Both FC and TR are reliable in detecting ASA in the urine of patients presenting with suspected drug overdose. A negative result with either test eliminates the need for a quantitative serum ASA level. Because FC has a longer shelf life than TR, it is the more practical reagent for use in the ED.