All about Drug tests
This guide serves to inform you of the different types of Drug tests available, what type of test to choose, and under which circumstances. Drugs can be divided into legally prescribed drugs like: Benzodiazepines (E.g. Valium), Opiates and other Analgesics, and Illicit drugs like: Amphetamines, Cocaine and Marijuana. Prescription drugs are often abused and can also be obtained illicitly. Individuals who are abusing drugs display clinical signs that are associated with the drug of abuse.
The laboratory is asked to test patient samples for drugs when drug abuse is suspected. There are 2 general test categories available: Screening tests and Confirmation tests.
- The screening test is to separate patients that are negative from those that are not.
- The samples that test not negative (i.e. positive) with the screening test, should be subjected to a confirmation test.
- The confirmation test will identify the specific drug present, or if the confirmation test is negative classify the screening test result as a false-positive screening test.
- Immunoassays are also available as a test performed by large automated analysers in the laboratory. The sample is placed in a tube/container and sent to the laboratory for testing.
- These tests are done for specific drug classes; these have to be specified on the request form. If more than 1 drug class is needed, for example cannabis and opiates, it has to be specified.
- This type of testing is quick; the tests pick up the drugs easily and are easy to perform. The result is reported as negative below a certain cut-off. This cut-off is often determined by the manufacturer, or a legal cut-off can be used.
- These tests are also prone to cross-reactions, as seen with Codeine and Morphine (both give positive opiate screening results).
- Another example is Valiumand Dormicum, both are Benzodiazepines, but they don't give the same screening result. Valium will give a higher result than a similar amount of Dormicum. Stocrin, an anti-retroviral agent, can give a false- positive cannabis result with certain test systems.
- Above the cut-off the result is reported as a numerical value. In urine samples, although the concentration of the drug is obtained, the result gives no indication of the physical state of the urine sample donor at the time of collection.
- As with near patient testing, laboratory testing is also inexpensive, however there are limitations to both types of screening tests.
- The limitations of all immunoassays, near patient and laboratory automated, include: only drug classes are tested (e.g. opiates), NOT the specific drug (e.g. codeine vs. morphine – the one a common pain killer, the other a highly controlled drug used for specific reasons).