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Drug Testing Methodologies

Once the sample arrives at the lab for analysis, the different types of drug tests are tested in very similar ways. Before testing the sample, the tamper-evident seal is checked for integrity. If it appears to have been tampered with or was damaged in transit, the lab rejects the sample and does not test it.

One of the first steps for all drug tests is to make the sample testable. Urine can be used "as is" for some tests, but other tests require the drugs to be extracted from urine beforehand. Strands of hair, patches, and blood must be prepared before testing. Hair is washed in order to eliminate second-hand sources of drugs on the surface of the hair, then the keratin in broken down using enzymes. Blood plasma may need to be separated by centrifuge from blood cells prior to testing. Sweat patches are opened up and the sweat collection component is soaked in a solvent to dissolve any drugs present.

Laboratory-based drug testing is done in a two-tiered fashion using two different types of detection methods. The first is known as the screening test, and this is applied to all samples that go through the lab. The second, known as the confirmation test, is only applied to samples that test positive during the screening test. Screening tests, usually done by immunoassay (EMIT for urine and blood, and ELISA for hair). The screening tests are typically less sensitive and more prone to false positives and false negatives than the confirmation test. Once a suspected positive sample is detected during screening, the sample is flagged and tested using the confirmation test. Samples that are negative on the screening test are discarded and reported as negative. The confirmation test in most labs (and all SAMHSA certified labs) is performed using mass spectrometry, and is extremely precise but also fairly expensive to run. False positive samples from the screening test will be negative on the confirmation test. Samples testing positive during both screening and confirmation tests are reported as positive to the entity that ordered the test. Most labs save positive samples for some period of months or years in the event of a disputed result or lawsuit.
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