Differentiating medicinal from illicit use in positive methamphetamine results in a pain population.

In addition to illicit methamphetamine, there are prescription and over-the-counter medications that, if ingested, may yield positive methamphetamine (MAMP) results on laboratory urine drug tests. The purpose of the study is to estimate the prevalence of medicinal and illicit MAMP in the pain population using chiral analysis to determine the relative amounts of the d and l-MAMP enantiomers. This retrospective analysis included the LC-MS/MS results and prescriber provided medication histories of 485,889 de-identified urine specimens from patients treated for pain. Two groups of 100 specimens each were subjected to chiral analysis. Group 1 contained specimens that were MAMP positive and amphetamine negative. Group 2 contained randomly selected MAMP positive specimens. The overall MAMP positivity rate of the 485,889 specimens tested was 1.6%. The prevalence of MAMP medications based on reported medications and detection of l-MAMP in Group 1 and Group 2 was 44% and 6%, respectively. These data indicate that the use of both illicit and medicinal MAMP is found in this patient population, and that medicinal use is underreported in clinical histories. Therefore, clinical laboratories should provide on request chiral analysis to aid in differentiating illicit and medicinal MAMP.