A multicomponent LC-MS/MS method for drugs of abuse testing using volumetric DBS and a clinical evaluation by comparison with urine.

BACKGROUND: Drug testing commonly use urine as a specimen and immunoassays for screening. The need for supervised urine collection has led to an interest in alternative specimens and a need for using mass spectrometry methods already for screening. In addition, mass spectrometry methods allow for broad multipanel screening which of great value because of the increased number of substances that needs to be covered has increased over time. One alternative specimen of interest for drugs of abuse testing is dried blood spots (DBS) and this work aimed at developing multipanel screening methods based on selected reaction monitoring liquid chromatography - mass spectrometry for both urine and dried finger blood as specimens.

MATERIALS AND METHODS: The urine method comprised 37 analytes and utilised salted out liquid/liquid extraction in 96-well format, respectively, and the blood method comprised 35 analytes, a 10 µL volumetric DBS device and a two-step solvent extraction procedure. In both cases stable isotope labelled internal standards were used for almost all analytes.

RESULTS: The methods were validated according to forensic standard. The lowest reporting limits were generally set at 100 ng/mL for urine and 1 ng/mL for blood and the accuracy and imprecision were within limits of 15 and 20%. The methods were applied in a clinical study on patients receiving methadone maintenance treatment for opioid dependence. Methadone was detected in all urine and DBS samples, for urine sometimes below the commonly applied screening cutoff limit of 300 ng/mL. In 20 out of 99 cases no other drug was detected in any specimen. The most commonly other detected substances were pregabalin, amphetamine, alprazolam, zopiclone and THCCOOH. Findings in urine and DBS generally agreed well but more positives were detected in DBS.

CONCLUSION: Multipanel methods using liquid chromatography - mass spectrometry suitable for clinical drug screening were successfully developed for urine and blood collected by finger-pricking and stored as DBS.