Automated analysis of dried urine spot (DUS) samples for toxicology screening

Dried specimens have been proposed in multiple environments to minimize costs associated with specimen storage and shipping in clinical studies. This report describes the development and validation of an automated method for qualitative toxicology screening of dried urine samples using LC-MS/MS.

Urine standards containing 41 compounds were prepared and applied to filter paper cards. Dried urine was eluted from the cards using a Dried Blood Spot (DBS) autosampler from Spark Holland, which was plumbed inline with a Thermo Scientific Turboflow chromatography system for subsequent MS/MS detection with selected reaction monitoring. Limits of detection, precision of peak areas, repeatability, and carryover studies were conducted. Concordance with a reference LC-MS/MS method using liquid samples was evaluated using remnant discarded specimens.

The limit of detection ranged from 5 to 75 ng/mL for most compounds. At the LOD for each analyte, the peak area precision ranged from 8 to 29%. For 20 repeat injections of samples spiked at ±25% of the LOD, there was a 4% false positive rate for the 75% × LOD samples, and a 0.4% false negative rate for the +125% × LOD samples. In comparing 40 known positive specimens analyzed with the DUS method and a liquid urine reference method, there was 88% agreement. Analysis of 10 known negative specimens yielded negative results. There was no significant carryover detected up to 2000 ng/mL for any of the analytes in the assay.

Using a robotic DUS sampling an inline HTLC-MS/MS system, we have developed and validated a fully-automated and robust method for multi-analyte detection of drugs of abuse in dried urine specimens.