Metabolites
When you ingest pharmacologically active substances, your body generally breaks them down in order to use them. The break down or use of these substances will produce chemical left overs called metabolites. Metabolites can be excreted or stored in the body. Common drug tests primarily look for these metabolites and in a few rare instances for the actual drug itself. How long metabolites remain in your system varies depending on the type and amount of drug ingested and on your individual biochemistry. Drug testing for athletic competitions is more complex because some of the chemicals tested for, certain hormones for example, occur naturally in the body and must be distinguished from synthetic chemical supplementation.
Samples
For most drug tests you will be asked to provide a sample of your urine, hair or blood. In emergency medical situations when overdose is suspected, your stomach contents may be tested. Collection procedures will vary depending on the end use of the test results. If you are responsible for an accident and it is suspected that you were under the influence of drugs, for example, legal protocols for procuring and securing evidence should be followed. In this case if you are providing a urine sample, you will be accompanied to the restroom and the urine sample will be immediately tested to make sure it is body temperature. If you are providing a blood sample, a trained phlebotomist or other medical professional will draw blood. If you are providing a hair sample, a trained professional will shave a small not-readily-noticeable area on your body or cut a sample of hair near the skin surface.
Screening
The first step in drug testing in employment situations is typically screening. A screening test looks for the presence or absence of a substance in an amount above a predetermined cutoff level. It is typically unconcerned with amounts of a substance present. A negative screening test does not mean that a person is not using nor has not used drugs, only that there is no biologically significant evidence detected at the time of testing; conversely, a positive urine screening test does not mean that a person was under the effect of drugs at the time of testing. False positives on screening tests are frequent and further investigation should always be pursued.
Testing
If a screening test is positive, additional testing should be pursued. In some instances, there is no preliminary screening. Additional testing frequently involves gas chromatography or mass spectrometry. The resulting report will indicate the drugs for which the sample tested positive. False positives are less likely with gas chromatography and mass spectrometry.
