An assay evaluation of the methylene blue method for the detection of anionic surfactants in urine.

Adding detergent to urine intended for drug testing is one of many ways to adulterate the specimen. This modified methylene blue procedure allows the detection and quantitation of anionic surfactants in urine. One-hundred urine specimens that exhibited normal foaming when shaken gave anionic surfactant values lower than 36 microg/mL with a mean of 8.73 microg/mL. Most of the suspected adulterated specimens and spiked samples with only 100 microL of detergent in 60 mL of urine had values greater than 750 microg/mL. Based on the analysis of negative samples, a urine specimen with an anionic surfactant level of 100 microg/mL or greater could be considered adulterated and most likely will have levels greater than 800 microg/mL.