Evaluation of the applicability of urine lateral flow immunochromatography tests for the detection of cocaine in plasma samples

Introduction

Qualitative analysis of cocaine in urine is a common practice in emergency settings. However, positive results from urine screening tests do not necessarily indicate recent exposure. In this context, plasma is considered a more appropriate option due to its shorter detection window and better correlation with symptomatology. Therefore, the availability of rapid tests for this biological matrix is extremely relevant in the clinical and emergency context.

Methods

A lateral flow immunochromatography test designed for analyzing cocaine in urine was evaluated for use with plasma samples. A total of 412 samples from suspected cases of intoxication were processed and tested. Concurrently, the samples were analyzed for cocaine and its metabolites, benzoylecgonine and ecgonine methyl ester, using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Reliability parameters, including sensitivity, specificity, positive predictive value, negative predictive value, and efficiency, were calculated considering different cutoff values.

Results

Approximately 8.3 % of the samples tested positive in the immunoassay, while 10.2 % had a concentration greater than 5 ng/mL for at least one analyte in the LC-MS/MS analysis. Using benzoylecgonine as the target analyte with a cutoff of 40 ng/mL yielded the best reliability results, with 96.3 % sensitivity and 97.9 % specificity. Cocaine did not show satisfactory results, whereas ecgonine methyl ester, despite having 92.9 % sensitivity and 94.7 % specificity at its best cutoff (20 ng/mL), had a positive predictive value of only 38.2 %.

Conclusions

The study evaluated the suitability of using rapid urine tests for cocaine detection in plasma, offering a simple and quick drug screening method that is particularly useful in toxicological emergencies.