A comparison of two bedside tests for the detection of salicylates in urine

Objective: Ferric chloride (FC) and Trinder reagent (TR) have both been use d to identify salicylates (ASA) in the urine of patients preventing with po ssible drug overdose. The authors sought to compare the sensitivities and s pecificities of these two reagents in detecting ASA in the urine of patient s presenting to an emergency department (ED) with suspected drug overdose. Methods: Patients were eligible for inclusion in this study if they present ed to the ED with either suspected overdose or unexplained metabolic acidos is. One milliliter of the patient's urine was added to 1 mt 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: T wenty of 180 patients (11%,) had quantitative serum ASA levels above 5 mg/d L. Both reagents were 100% sensitive in identifying these patients. The spe cificity of FC was 71% compared with 73% for TR. The two reagents gave simi lar results in 91% of cases. Conclusion: Both FC and TR are reliable in det ecting 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 mor e practical reagent for use in the ED.