Creatinine serves as a marker for urine concentration. It is a waste product generated from muscle metabolism and is consistently produced and excreted by the kidneys. The measurement of its level in a urine sample is essential to ensure the validity of drug testing results. An acceptable range typically falls between 20 mg/dL and 300 mg/dL. Values outside this range may suggest the sample is diluted or adulterated, thus rendering the drug test result unreliable.
The presence of creatinine in urine, within the established parameters, confirms that the sample is indeed urine and that it has a sufficient concentration to accurately detect the presence of drugs or their metabolites. Monitoring its level has become an integral component of standardized drug testing protocols. Historically, the inclusion of this measurement has enhanced the defensibility and accuracy of drug testing programs, providing a standardized method to identify manipulated or invalid samples.