False positive of usingurine methamphetamine color test and immunoassay test

Abstract

The Thai government announced lows to prohibit and prevent growing use of methamphetamine or Yaba. Detection of amphetamine in urine is method use by Thai criminal justice system and brought drugs users back to have medical treatment. Policeman arrestd suspected-drug user by detecting Yaba in urine using color test or immunoassay test. If the on-site screening tests gave positive result, the samples were sent to the central laboratory for confirmation. This descriptive cross sectional study was
conducted at Lampang Hospital in order to determine a false positive rate of amphetamine screening test during July-October 2007.
Demographic data of drug users and amphetamine test results were collected from Lampang Hospital database and documents at police stations in year 2004 and 2006. Gas chromatography was used as a confirmation method for all screened-positive asmple. The central laboratory detected 173 and 321 Yaba users in 2004 and 2006, respectively. There were 440 males and 54 females with an age ranging from 15 to 56 years (mean 27.4). In 2004, false positive rate of urine color test were higher than immunoassay tests
with SureStep TM, significantly (32.5% vs. 4.1%, p<0.001). Where as in 2006 when police atation used a different product of immunoassay test (GPO), the false positive rate of urine Yaba between color test and GPO were comparable (36.1% vs. 32.8%, p=0.613). However, when compared using immunoassay test between SureStepTM in year 2004 and TriV@ in year 2004 and Tri=V@ in year 2006, the false positive were increased significantly from 4.0 to 21.1, respectively (p=0.006). False positive rate of urine color test was found approximatly one-third, where as immunoassay test (Tri-V@) was found approximatly one-fifth. Thus immunoassay with Tri-V@ and/or SureStepTM should be used to detect urine methaamphetamine wherever possible.