Quality Evaluation of Urine Methamphetamine Color Test and Immunoassay Test

Abstract

Nowadays, Yaba or methamphetamine drug abuse becomes critical social problem in Thailand, particularly among school children, collage students and blue - collar workers. Methamphetamine urine test kit was an important equipment for screening test to detect Yaba in drug urine users. The research was descriptive cross sectional study conducted from October 2010 to September 2011. The objective of this study was to evaluate the sensitivity, specificity, accuracy and false positive results by using color test and immunoassay test with four different test kits in Nakhon Nayok Hospital. Three were screening test products of Thailand and one was imported. Screening tests were confirmed by thin layer chromatography. A total of 900 urine samples were sent for drug trial. It was found that the sensitivity, specificity and accuracy of urine color test were lower than those of immunoassay tests. False positive rate of urine color test were higher than that of immunoassay tests, significantly (p < 0.001). All immunoassay test kits in this study were reported with high sensitivity, specificity and accuracy. The imported product had the highest sensitivity (99.49 %), specificity (95.19 %) and accuracy (98.00 %) but it yielded the lowest false positive rate (4.81%). Accuracy of an immunoassay based on methamphetamine test kits were higher than that of the color test kits because the principle of immunoassay test was biochemical reaction while the color test was only chemical reaction thus the immunoassay test showed higher specificity to drug abuse than the color test. On top of this, color test had limited detection capability of method (cut off value 3,000 ng/ml) which is higher than immunoassay test (cut off value 1,000 ng/ml). These limits had direct impacts as the color test also had lower sensitivity than the immunoassay test. In selection of methamphetamine test kit for operation, quality assurance of the test compared to the standard method is highly recommended particularly in case of apprehension, legal prosecution and compulsory drug abuse rehabilitation that follow. With high accuracy of methamphetamine test kit laboratory reports become more reliable and unbiased As such, all screening units for drug abuse should use comparable high quality test kits.