A metabolite is what a drug is transformed into as it is broken down, processed, converted into active or inactive chemicals, and then eliminated by the body. This process largely takes part in the liver, which houses the enzymes necessary to perform this task. In immunoassay drug testing, the specimen is evaluated for presence of drug metabolites.
When the body breaks down a drug, changes it into active or inactive chemicals, and eliminates it - a process also known drug metabolism - what results is a drug metabolite. The enzymes required to metabolize drugs into metabolites are found in many tissues, but are most heavily concentrated in the liver. The rate at which drugs are converted into metabolites varies among individuals, and typically as a person ages, the liver's ability to metabolize drugs can be diminished by more than thirty percent. During immunoassay drug testing, what the sample is being evaluated for is the presence of drug metabolites, which is expressed in either positive or negative terms. At this stage, only the class of drugs that the metabolites correspond to can be determined, not the specific drug or quantity of that drug in the specimen.