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Does THC Show Up in a Routine Blood Test?

If you're an MMJ patient and your doctor has requested a routine blood test, you may be concerned about the results; but does weed show up in routine blood work? Contrary to popular belief, blood tests don't reveal all the compounds found in the blood and therefore it's unlikely that THC will show up on your results.


Indeed, the presence of THC won’t appear unless the blood test is specifically looking for it in your blood. Other types of tests including saliva tests are also used to detect THC in some circumstances and may be able to detect consumption as far back as several weeks.


What Do Blood Tests Show?


Doctors usually order blood tests to investigate specific symptoms a patient is suffering. This is because a blood test can reveal many possible causes for disease. It's unlikely that your doctor will test for marijuana use as a cause of your symptoms—especially if you haven’t mentioned your MMJ patient status to him or her.


THC will only show up in a blood test that is looking for THC. Sometimes specific tests looking for THC will be ordered. However, these aren't routine. 


Common Blood Tests Ordered by Doctors


There are several blood tests frequently ordered by doctors, including:


Complete Blood Count (CBC)

A CBC shows the levels of different types of blood cells including red and white blood cells, platelets, and hemoglobin.


Basic Metabolic Panel (BMP)

This test is used to indicate how major organs like the heart, kidneys, or liver are functioning. A BMP also checks blood sugar levels and electrolytes.


Complete Metabolic Panel (CMP)

The CMP includes the same tests as a basic metabolic test as well as a test for proteins. This provides information about liver function.


Thyroid Function Test

This test shows hormone levels in the blood and helps determine if a patient is experiencing a thyroid disorder, protein deficiency, or abnormal testosterone or estrogen levels.


Blood Enzyme Tests

Patients who have recently suffered chest pain can take this test to identify a possible heart attack.


Lipid Panel

A lipid panel measures cholesterol levels and indicates a patient's risk of heart disease.


None of these routine blood tests would pick up on marijuana use because they’re looking for other components in the blood to explain the patient’s health problems. They are not looking for THC metabolites.


Blood Tests that Look for Cannabis Use


Routine blood work won't look for cannabis. However, blood tests to detect cannabis are frequently used in medical screenings in psychiatric units or addiction rehabilitation centers. This is because cannabis use could interfere with the patient’s treatment or recovery.


Some workplaces are also obliged by federal law to subject workers in high-risk jobs to drug testing. These tests will look for THC metabolites as part of a broader drug screen panel. Members of the military and athletes are also subject to random drug testing.


If you consume hemp-derived THC products, be aware that Delta-10 THC will probably show up on a blood test. The same goes for Delta-8 THC.


Arizona’s MMJ Patient-Friendly Policies

The vast majority of medical marijuana cardholders in Arizona don’t need to be concerned that their MMJ use will put their job in danger. This is because you can get a job with a medical marijuana card in Arizona, as long as the job is not for the federal government or is a “safety-sensitive” job. You aren’t obliged to disclose your MMJ use in a job interview and potential employers are not allowed to ask. 


Notable exceptions to this—as hinted at above—include safety-sensitive roles like pilots, air traffic controllers, drivers, and police officers. Teachers who get an MMJ card are also at risk of facing sanctions (regardless of the fact that they have an AZ qualifying condition) and are therefore discouraged from consuming cannabis. This is because districts that hire an MMJ user could potentially lose their federal funding.


How Long Does THC Stay in the Blood?


Marijuana typically only remains in the bloodstream for up to 12 hours. For that reason, blood tests aren't typically used for detecting THC in the system. The THC you consume reaches the bloodstream within minutes of inhalation but then rapidly decreases in the 3-4 hours after consumption.


However, frequent or heavy use may extend the detection window. Chronic cannabis use or heavy consumption on one day can lead to THC showing up in your blood for up to 7 days. 

Apart from frequency of use, the length of time THC stays in the body will depend on several factors. These include:


  • The level of THC in the marijuana

  • How often and how much you consume THC

  • How sensitive the drug test is

  • Your metabolism rate

  • Whether you inhaled or ingested THC


Other Drug Tests to Detect THC


Because THC stays in the bloodstream for such a short amount of time, positive tests are more probable with other methods of testing.


Urine Tests

Urine tests are the most frequently used test when someone is looking for the presence of cannabis. A urine test provides a long detection window that spans from a few days to as long as several weeks after the last use. False positives are very rare. The amount of time somebody can test positive on a urine drug screen will differ from person to person.


Saliva Tests

According to a paper published in the Griffith Journal of Law & Human Dignity, saliva tests can detect THC for about 12 hours after use in people who consume cannabis infrequently. The test may be able to detect THC for up to 30 hours in chronic cannabis users (this can include MMJ patients). Roadside tests to detect marijuana using oral fluid can also pick up the presence of other drugs like Methamphetamine and MDMA.


Hair Tests

A hair test can detect THC use in the past 90 days, but not recent use (in the last 7 days).


Sweat Tests

Sweat tests are another alternative, non-invasive way to test for marijuana use. THC can show up in this test for one to two weeks.


THC Detection Windows: Summary

Type of Test

Blood

Urine

Hair

Saliva

Sweat


Up to 12-24 for infrequent use. Up to 7 days for heavy or frequent use.

1-30 days

Up to 90 days

Up to 24 hours (or up to 30 hours as per the source cited earlier)

7-14 days


Source: Hadland, S.E., & Levy, S. (2016). Objective Testing - Urine and Other Drugs. 

Child and Adolescent Psychiatric Clinics of North America, 25(3), 549–565. https://doi.org/10.1016%2Fj.chc.2016.02.005


Most Blood Tests Aren’t Looking for Cannabis


A regular blood test looks for some of the most common markers of health and isn’t looking for THC metabolites. You can check the blood test order from your doctor to see which markers will be tested.


Workers in certain industries may be subjected to drug tests as stipulated in their contract. If you regularly take cannabis products for medical or adult-use purposes, ensure clear communication with your employer from the outset to avoid any surprises down the road.


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