How a Blood Test is Performed for Detection of Marijuana

by Debbie Harry

Marijuana drug test is essential for determining if a person has consumed the drug. It is done by collecting samples which may be urine, blood, saliva and hair. Let us now know about a blood test which is performed for detecting marijuana.

The active presence of tetrahydrocannabinol (THC) can be known through blood test. The levels of THC in blood plasma are higher with a concentration of 100ng/ml. The concentration remains higher at the time of consumption and declines rapidly. However, when marijuana testing is done through blood tests, the drug can be detected at a level of 1-2ng/ml for eight hours or more.

Detection of THC by blood tests acts as useful indicator for marijuana usage. High amounts of THC in blood indicates that the person has consumed marijuana recently. This can be helpful in certain cases such as road accidents, workplaces and autopsy.

Apart from THC, its metabolite carboxylic THC can also be detected through blood tests. It can be detected for a couple of days for a single use of drug. However, in chronic users, it can be detected for a few weeks. Hence this may not be used as a valid indicator for confirming the drug usage. Another metabolite called 11-hydroxy-THC can be detected through blood tests. It is a byproduct which is produced by processing of THC in liver after oral consumption of the drug.

Blood tests for marijuana drug tests are conducted at various organizations. Many drug test kits are generally available that can be used at home. However, these are not available for performing blood tests as the administration of sample is difficult. Also these tests require proper laboratory analysis for achieving proper results.

The cost of blood test for marijuana is relatively higher. It also involves a long procedure that lasts for about four to six days.


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