A blood test measures the amount of certain drugs in a person’s bloodstream at the moment the test is administered. It is one of the surest ways of confirming whether a person is or has been using drugs.

There are a number of circumstances where officials use drug testing through bloodwork, including as pre-employment drug testing, testing athletes for performance-enhancers, and testing following an on-the-job accident.

Drug testing through bloodwork is recognized as the most accurate way to determine whether someone is intoxicated. However, because it is costlier and more invasive than other drug tests, it is seldom used in an employment setting.

Other forms of drug testing by employers is relatively common in the United States, but in Canada, few employers have the legal grounds to test employees for drug use either before or during the course of employment.

How Drug Testing Through Bloodwork Works

To test for drugs, a medically-trained administrator draws a blood sample from the person to be tested using sterile equipment. Since this requires specialized tools and training, it should only be done by a professional (click here to find out if there is a service in your area.)

Once the sample is collected, it is sent to a certified laboratory to be subjected to an immunoassay test. This determines whether there are drugs or metabolites in the sample. If the test flags the presence of a drug, it is then screened using a gas-chromatography-mass-spectrometry (GC-MS) machine to confirm and measure the amount of the drug.

The two-step process of drug testing through bloodwork ensures accuracy and reduces the chance of false positives.

Depending on the purpose of the test, administrators may screen for a specific drug or a number of different drugs. Many employers use what is known as a five-panel test, which screens for amphetamines, cannabis, cocaine, PCP, and opiates. Others use a broader nine or ten-panel test that also looks for certain prescription drugs that are known to be used for recreational use.

How long a drug stays in a person’s system depends on a number of factors. Drugs with a longer half-life will be detectable for longer after use, and it can vary between individuals based on things like hydration and frequency of use.

The results of drug testing through bloodwork can take between a few days and a few hours, depending on the laboratory in which is processed.