A new automated assay for the detection of synthetic urine in drug testing

Urine drug testing can be subject to attempts to dilute, adulterate, or substitute the specimen. Substitution may involve the use of commercially available synthetic urine. Current laboratory methods to detect specimen validity often fail to detect these products. We evaluated a new automated assay designed to detect synthetic urine. We determined that the assay met performance requirements and accurately identified five commercially obtained products as synthetic urine while not identifying known normal urine as synthetic. However, in a group of 843 patient urine samples, 40 of the 46 urine samples identified as "synthetic" were samples with creatinine <50 mg/dL. Fourteen of the 40 were actually positive for drugs of abuse. We conclude that the test is analytically valid but clinically limited. We recommend that it be used in conjunction with other indicators of synthetic urine. We suggest a scheme that would achieve this, and reporting terminology that would reflect the limits of the analysis.