Beating the system: a study of a creatinine assay and its efficacy in authenticating human urine specimens.

Creatinine concentration is commonly used to verify the authenticity of urine specimens submitted for illicit drug screening. This study evaluated creatinine screening of donor urine specimens as a tool for detecting substituted and/or tampered specimens. The study carried out creatinine assay of animal urine, fruit juices, and urine from creatine-supplemented subjects by a modified version of the Jaffe reaction. All specimens were analyzed for creatinine concentration in a chemistry-immuno analyzer. Results showed that urine specimens from common domestic pets, including cats, dogs, and horses, have creatinine values similar to normal human values. Most fruit juices tested contained no detectable creatinine, and the few that did showed poor "urine" chemical integrity. Creatine supplementation by donors was found not to provide an effective means of elevating creatinine concentration in urine when attempting to flush out water-soluble drugs in the body. Thus, the assay for creatinine proved useful for the detection of some but not all adulterated urine specimens.