Does Marijuana Show Up in Regular Bloodwork?
Article written by
Ruth LemonVP of Operations
Content reviewed by
Dr. Lewis JasseyMedical Director - Pediatric Medicine
It’s unlikely that marijuana will appear on blood tests as part of a medical appointment.
Tests for cannabis use generally look for a THC metabolite in your system. A regular blood test ordered by your doctor is unlikely to check for drug use unless they think your symptoms match those caused by a particular drug.
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What Do Blood Tests Show?
Contrary to popular belief, blood tests don’t analyze every single compound in the blood.
If you go into the doctor’s office for a blood test, they’ll listen to your symptoms and think of possible causes. When ordering a blood test, they’ll look into specific tests that could explain them. Each blood test costs money and requires a separate sample, and it wouldn’t make sense to test for every possible outcome if a few would only explain your symptoms.
As a result, unless you have symptoms caused by marijuana use, your doctor likely won’t test for it.
But medical diagnosis isn’t the only reason for a blood test; some tests specifically look for drug use. You’ll always be told about any drug testing, though.
Common Types of Blood Tests
There are many different kinds of blood tests, but the ones that doctors most commonly order are as follows:
Complete Blood Count (CBC)
A complete blood count looks into the levels of different blood cells, including:
- Red blood cells. These are the oxygen-carrying cells in the blood. The level of red blood cells indicates how hydrated a person is and whether they might be suffering from anemia or a bleeding disorder.
- White blood cells. These are the cells of the immune system. The amount of white blood cells indicates whether a person suffers from an infection, blood cancer, or an immune disorder.
- Platelets. Platelets help the blood clot to prevent excessive blood loss when bleeding. High levels could indicate a clotting disorder, while low levels indicate a bleeding disorder.
- Hemoglobin. Hemoglobin is a protein found in red blood cells that help them carry oxygen. The relationship between red blood cell count and hemoglobin levels gives information on the type of anemia someone might suffer from.
- Hematocrit. Hematocrit describes the amount of space taken up by red blood cells, and this can also give more specific information on hydration and potential anemia.
- Mean cell volume. Mean cell volume refers to the average size of the red blood cells. Like hemoglobin and hematocrit, this gives just a bit more information on what type of anemia someone might have.
Basic Metabolic Panel (BMP)
A BMP includes blood sugar levels, electrolytes, and organ function tests. The results of a BMP indicate how organs such as the heart, kidney, and liver are currently functioning.
Complete Metabolic Panel (CMP)
A CMP includes all the same tests as a BMP and tests for proteins to indicate liver function, such as albumin, total protein, ALP, ALT, AST, and bilirubin.
Thyroid Function Test
The thyroid function test checks how much T3, T4, and TSH are in the blood. These hormones can help determine if someone is experiencing protein deficiency, a thyroid disorder, or abnormal testosterone or estrogen levels.
Blood Enzyme Tests
Blood enzyme tests (like CK-MB and troponin) are often taken at the hospital to test if someone who’s recently experienced severe chest pains was suffering from a heart attack. That allows clinicians to decide whether further tests for heart damage are needed.
Lipid Panel
A lipid panel blood test measures cholesterol levels (including total, HDL, and LDL) and triglycerides. Its purpose is to measure a patient’s risk for heart disease.
For more information on different types of blood tests, read these articles: Blood Tests and 10 Important Blood Tests.
Blood Tests That Detect Marijuana Use
Blood tests that detect marijuana use are often done for medical screening of patients in psychiatric care or addiction rehabilitation centers, as they are in a position where marijuana use may interfere with other medications or prevent their recovery.
In some areas, workplaces are required by federal law to subject employees who work in high-risk jobs to undergo drug testing.
Tests for marijuana look for the presence of a metabolite of THC, which is thought to be responsible for its psychological activity. They are usually part of a broader drug screen panel. Marijuana use is generally only detectable for up to seven days but can be found longer than 30 days in chronic users.
The Bottom Line
Most blood tests ordered by a doctor will not detect cannabis use. Unless your doctor thinks that you may be experiencing symptoms related to cannabis, for example, that it might interact with other drugs you’re taking, they likely will not test for it.
An employer can require that you take a drug test to detect cannabis use or a doctor to test for cannabis use, but you will likely be made aware of this being part of the test. If you are tested for cannabis use, your positive result will depend on what kind of cannabis products you use, how regularly you use them, and when you last took them.
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