How do windows of detection differ between oral fluid and urine?
Windows of detection are generally shorter in oral fluid than in urine. The windows more closely parallel windows of detection in blood. Blood concentrations of many drugs fall rapidly because of metabolism by the liver or elimination by the kidney. Since parent drugs, rather than metabolites, are measured in oral fluid, the life-time of parent drugs may be shorter. The drug metabolites continue to be excreted in the urine, where they are concentrated by the kidney and collect in the bladder for hours. Thus, urine may provide a longer window of detection for drug metabolites.
