RESUMEN
Sixty-two urine samples from truck drivers and drug addicts were analysed by TDx (Abbott Laboratories) for amphetamines. Eighteen samples were found to be positive while the rest were negative. The eighteen samples were simultaneously determined for amphetamines by EMIT (Syva Company). Sixteen samples were found to be positive and 2 of negative samples had amphetamines levels of 0.48-0.85 micrograms/mL. When the same samples were subjected to qualitative screening and some were found false negative as follows: 7 cases in Color Test by using test solution kits amphetamine in urine (the Department of Medical Science, Ministry of Public Health), 8 cases by Albuscreen Ontrax for amphetamine (Roche Diagnostic System), 5 cases by amphetamine Double Antibody 125I-RIA (Diagnostic Products Corporation-DPC) and 3 cases by the method of Ten-One (DPC) respectively. But when forty four samples which gave negative results by TDx were subjected to Testing by EMIT and Ontrax. The results of both EMIT and Ontrax were negative. Some of forty four samples were false positive by the Color Test solution kit amphetamines in urine and amphetamine Double Antibody 125I-RIA. Reliability of results reported not only depends on the methodology or principle but also the sensitivity of the method.