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Drug Screening

THC-COOH in blood: the limits 5, 73 and 137 and what they say

THC-COOH is called a cannabis metabolite by Certe and tetrahydrocannabinolic acid by Unilabs: a metabolite is a substance formed when the body breaks down another substance, here from cannabis. According to Trimbos, hash and weed come from the female cannabis plant and make someone high or stoned, with a feeling of relaxation and calm, but can also make someone anxious or panicky.

According to Trimbos, someone who uses cannabis heavily and often has higher values in the blood, and a blood test for THC-COOH can see for longer whether someone has used cannabis than a test for THC. Only a blood test shows how much THC-COOH is in the blood.

Unilabs reads THC-COOH below 5 ug/L as negative, 5 - 73 ug/L as light use, above 73 ug/L as an indication of heavy use and above 137 ug/L as a strong indication of it.

Doctor's Assessment Included

THC-COOH is a cannabis metabolite that, according to Trimbos, a CBR blood test uses to see whether someone uses cannabis and whether that is a lot or a little.

  • Star-SHL reads THC-COOH below 5 ng/ml as negative, Unilabs below 5 ug/L, and Certe uses 0 - 5 ug/L.
  • Unilabs reads above 73 ug/L as an indication of heavy use and above 137 ug/L as a strong indication.
  • According to Trimbos, THC-COOH can be positive in blood for a number of days up to two months after use.

Cannabinoids (THC): what Dutch laboratories use

There is no nationally agreed reference value; this is what individual laboratories publish.

Reference ranges by group, in ng/ml
Star-shl · Everyone · a limit, not a range · negative < 5 ng/ml
5
Unilabs · Everyone · a limit, not a range · negative < 5 µg/l
Certe · Everyone 0–5 ug/L
0 5.5 ng/ml

Source: Star-shl

Source: Unilabs

Source: Certe

Each value as the laboratory itself publishes it, retrieved in 2026.

Cannabinoids (THC): what this test measures

A THC-COOH result gives the amount of cannabis metabolite in plasma or serum, in ng/ml at Star-SHL and in µg/l at Unilabs; both measure with LC-MS/MS.

Cannabinoids (THC): why this value matters

THC-COOH matters in a driving licence assessment, because according to Trimbos the CBR uses blood tests to check whether someone uses cannabis and whether that is a lot or a little; the psychiatrist judges this and also looks at other information.

Cannabinoids (THC): how the blood test works

Referral
No GP referral needed. After the order we arrange the referral through ZorgDomein, within one business day; orders after 17:00 or at the weekend start on the next business day. ZorgDomein emails a barcode, and that barcode is what the draw site needs.
The draw
A blood draw from a vein in the arm, at a partner laboratory's draw site. No home kit, no finger prick.
Where
650+ draw sites run by independent laboratories across the Netherlands. Draw sites

Cannabinoids (THC): when is testing worthwhile?

According to Trimbos, a blood test for THC-COOH can be positive for a number of days up to two months after use, while a police blood test for THC can be positive about 4 to 24 hours after use.

Cannabinoids (THC): symptoms of a high or low value

Low Levels

A THC-COOH below 5 ng/ml is negative at Star-SHL, and according to Trimbos it is hard to determine exactly how long someone tests positive, because it differs from person to person.

High Levels

Star-SHL calls a THC-COOH of 73 ng/ml or higher an indication of heavy, chronic and long-term excessive cannabis use, and 137 ng/ml a strong indication.

Cannabinoids (THC): causes of a low or high value

What lowers the value

  • Use longer ago or light use

    Whether someone tests positive for a number of days or for two months depends on how much and how often cannabis was used before the test, and it differs from person to person.

What raises the value

  • Cannabis use in the days up to two months before the test

    Someone who has to take a CBR blood test can test positive for a number of days up to two months.

  • Heavy and frequent cannabis use

    Above 73 ug/L, THC-COOH is an indication of heavy (chronic, long-term excessive) use, above 137 ug/L a strong indication.

  • CBD products containing too much THC

    It sometimes happens that CBD supplements contain too much THC and that this gives a positive test; CBD itself probably does not cause a positive drug test.

  • Medicinal cannabis or cannabis oil

    Medicinal cannabis (Bedrocan) or cannabis oil (Bedica or Bediol) can cause a positive cannabis test.

Cannabinoids (THC): lifestyle and this value

Discuss a positive THC-COOH result with your GP and mention medicinal cannabis or cannabis oil if you use them, because Trimbos names them as products that can give a positive cannabis test.

Cannabinoids (THC): frequently asked questions

Can someone test positive without being a heavy user?

Yes, in a CBR assessment, according to Trimbos, someone can test positive for THC-COOH without being seen as a (heavy) user.

Cannabinoids (THC): sources

  1. Star-shl, Labbepalingen (referentiewaarden per bepaling), star-shl.nl, geraadpleegd 2026-10-01 (retrieved 2026) star-shl.nl
  2. Unilabs, Bepalingenklapper (referentiewaarden per bepaling), bepalingenklapper.nl, geraadpleegd 2026-10-01 (retrieved 2026) bepalingenklapper.nl
  3. Certe, Bepalingenwijzer (referentiewaarden per bepaling), bepalingenwijzer.certe.nl, geraadpleegd 2026-10-01 (retrieved 2026) bepalingenwijzer.certe.nl
  4. Trimbos-instituut, DRUGSinfo: Hasj en wiet, aantoonbaarheid in speeksel, bloed en urine, drugsinfo.nl, geraadpleegd 2026-10-19 (retrieved 2026) drugsinfo.nl

Tests with related values

These panels measure values from the same category as this marker.

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Cannabinoids (THC)

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