Creatinine analysis in single collection urine specimens

Controlled and uncontrolled fluid intake studies were conducted on series of volunteers over the 6 or 12 h of the study periods. Urine specimens were obtained from each subject randomly or at specified times relative to fluid ingestion. Creatinine analysis performed by a modification of the Abbott TDx procedure demonstrates that the values obtained from single collection specimens fall almost in the same range as the values from 24 h pooled collection specimens. The creatinine concentration can be used to indicate possible adulteration of urine specimens by dilution as a means of avoiding detection of use of drugs of abuse. Between 4 and 7 h are required for a decrease in creatinine concentration to about 100 mg/dL from an initial mean of about 170 mg/dL. A minimum of 6 h is needed for any creatinine value to fall to 50 mg/dL or less. Thus, it appears that creatinine output is sensitive to the amount of fluid ingested, but the relationship is neither linear nor immediate. The absence of a significant creatinine concentration in a specimen can be used as an indication of direct or indirect adulteration of the urine specimen by dilution or replacement with water. At NDSL-Great Lakes, a decline of the creatinine concentration to 30 mg/dL is used as a cutoff for differentiating between urine specimens that might have been tampered with to avoid detection of drug use and those specimens that are dilute for other reasons. Values at 10 mg/dL or less are suggestive of replacement by water. The information is provided to local commands for investigation prior to initiation of punitive action by the command.