Cannabis Metabolite in Blood: What Tests Detect and How Long It Lasts
The main cannabis metabolite in blood is THC-COOH, an inactive THC breakdown product. Learn detection windows, cutoffs, and what a positive result means.
Most labs that test blood for cannabis use a positive cutoff of roughly 1 to 2 ng/mL for delta-9-THC and about 5 to 15 ng/mL for carboxy-THC, the main metabolite. Unlike urine testing, there is no single federally mandated blood cutoff, so cannabis blood test cutoff levels are set by the individual lab, employer, or testing program handling your sample.
cannabis detection time in blood
What a cutoff level actually is
A cutoff, also called a threshold or limit of positivity, is the concentration of a drug or metabolite above which a result is reported as positive. It is measured in nanograms per milliliter (ng/mL). Anything below the cutoff is reported as negative, even if a trace of the compound is technically present.
how long can cannabis be detected in blood
Two numbers usually matter: the screening cutoff used by a fast immunoassay, and the confirmation cutoff used when a sample is re-run on a more precise instrument such as LC-MS/MS. Confirmation cutoffs are generally equal to or slightly higher than screening cutoffs.
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Typical cannabis blood test cutoff levels
- Delta-9-THC (the parent drug): commonly 1 to 2 ng/mL, with some sensitive assays reporting down to 0.5 ng/mL.
- 11-hydroxy-THC (active metabolite): often 1 to 5 ng/mL.
- Carboxy-THC / THC-COOH (inactive metabolite): frequently 5 to 15 ng/mL, and up to 20 ng/mL at some labs.
These figures are ranges, not a universal standard. A lab that reports a 1 ng/mL cutoff for THC and one that reports 5 ng/mL can return different answers on the same blood draw.
Does Cannabis Stay in Blood Longer Than Urine?
How blood cutoffs compare with urine and saliva
Blood concentrations are far lower than urine concentrations, which is why blood cutoffs sit in the single digits while urine cutoffs are much higher.
- Urine: federal workplace guidelines use a 50 ng/mL screening cutoff and 15 ng/mL confirmation cutoff for THC metabolite.
- Blood: typically 1 to 2 ng/mL for THC and 5 to 15 ng/mL for carboxy-THC, since plasma levels are low and short-lived.
- Saliva: often 1 to 4 ng/mL for THC, with a short detection window similar to blood.
Blood testing is also less common than urine testing for pre-employment screens. It shows up more often in clinical settings, post-accident testing, and investigations of recent use.
How long THC stays above a blood cutoff
Delta-9-THC clears from blood quickly. After a single session, the parent drug is typically near or below common cutoffs within a few hours, and most casual users fall under detection within roughly 12 to 24 hours. Carboxy-THC lingers longer, often 1 to 3 days after occasional use and longer in daily, heavy users.
Because blood cutoffs are so low, a sensitive lab can still detect metabolite well after the psychoactive effects have worn off. Detection is not the same as impairment, and a positive blood result does not by itself prove when someone last used.
Factors that shift a blood result
- Frequency of use: daily use builds a larger body burden and extends detection.
- Potency and dose: concentrates and high-THC flower deliver more drug per session.
- Route of use: inhaled products peak fast and fall fast; edibles produce a slower, flatter curve.
- Body composition and metabolism: fat mass and individual enzyme activity change clearance speed.
- Time since last use: the single biggest variable in any blood result.
- Assay sensitivity: a lab with a 0.5 ng/mL cutoff will catch what a 5 ng/mL lab misses.
Practical points if you are facing a blood test
Ask which lab is running the test and which cutoff applies, since that number determines the outcome more than anything else. Home drug tests are built for urine and do not reflect plasma concentrations, so they are a poor guide here. Hydration and dilution tricks that sometimes affect urine samples have little effect on blood, because plasma concentration is regulated by your body rather than by fluid intake.
If a result carries consequences for a job, a custody matter, or a medical decision, ask for the confirmation value and the cutoff in writing, and discuss the result with a clinician who can interpret it in context.