The older versions of immunoassays required the lab personnel to mix one or more reagents together with the sample. These reagents often had to be kept in the refrigerator. This means that following the confirmation test, the laboratory reports the exact number of nanograms per militre of the drug present in the sample. If the number is lower than the NIDA cutoff for that drug, then the report is negative. The confirmation test can conclusively rule out false positives and can also identify the presence of adulterants, such as bleach, salt and soap.
Drugs stay in the body for various periods of time.
Some drugs such as cocaine are metabolized very quickly. Other drugs such as marijuana are stored in the body for more than a month. To answer this question we have to refer to the drug test being conducted. Most drug testing for probation, employment, accidents, and treatment are conducted with tests that conform to the NIDA standards. These standards are uniformly accepted by government and industry.