Calculate urine THC-COOH/creatinine ratios for a single sample or compare two specimens to assess normalized changes over time in urine.
Disclaimer: Educational use only—this is not medical, toxicology, legal, or employment advice. Urine testing typically detects THC-COOH (not active THC) and a single creatinine-normalized result cannot determine impairment, fitness to drive/work, or timing of use. For interpretation, consult the testing laboratory/Medical Review Officer (MRO) and/or a licensed clinician.
Limitations
- This calculator only normalizes a measured urine THC-COOH (cannabinoid metabolite) concentration to creatinine; it does not determine “new use vs residual” from one sample.
- Specimen validity/dilution criteria and reporting conventions can vary by lab/testing program; follow the laboratory’s guidance.
- Meaningful interpretation often requires serial samples plus chain-of-custody/testing context and professional review.
References and further guidance
- For applicable workplace testing, follow your program’s policies and laboratory specimen-validity criteria. See Mayo Clinic Laboratories’ THC-COOH/creatinine guidance for serial-test context and restrictions.
- For personal/clinical questions, ask the ordering clinician and/or the performing laboratory for interpretation notes.
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THC-COOH / Creatinine Ratio Formula
The calculator normalizes urine THC-COOH to urine creatinine. This helps adjust for urine dilution or concentration.
- Normalized Ratio is the creatinine-normalized THC-COOH result, reported as ng/mg.
- THC-COOH is the urine THC metabolite concentration, converted to ng/mL.
- Creatinine is the urine creatinine concentration, converted to mg/mL.
For the two-sample comparison, the calculator first finds the normalized ratio for each sample. Then it compares Sample 2 to Sample 1.
- Sample 1 Ratio is the normalized THC-COOH/creatinine result for the first specimen.
- Sample 2 Ratio is the normalized THC-COOH/creatinine result for the second specimen.
- Change Ratio shows how many times larger or smaller Sample 2 is compared with Sample 1.
- Percent Change shows the increase or decrease from Sample 1 to Sample 2 as a percentage.
The single-sample function reports one normalized value and a descriptive creatinine concentration guide. The comparison reports both normalized values, Sample 2/Sample 1, percent change, and the recorded collection interval. If Sample 1 is zero, relative change is undefined; both sample values remain available. Use measured numeric THC-COOH results, not zero substituted for “not detected” or “less than” reports.
Creatinine Status and Unit Reference
The legacy 20/300 mg/dL boundaries below are descriptive concentration flags after conversion to mg/dL, not a universal clinical reference interval or a specimen-validity decision. Follow the laboratory’s range and program criteria. Creatinine alone does not establish dilution or substitution; applicable criteria also use specific gravity.
| Creatinine in mg/dL | Status | Meaning for interpretation |
|---|---|---|
| Less than 20 | Low | The specimen may be dilute. |
| 20 to 300 | Within legacy guide | This value falls within the calculator’s legacy guide; it does not establish specimen validity or a normal clinical result. |
| Greater than 300 | High | The specimen may be concentrated. |
Use these conversions if your report uses a different creatinine unit.
| Input unit | Conversion used | Example |
|---|---|---|
| mg/dL creatinine | mg/mL = mg/dL × 0.01 | 100 mg/dL = 1 mg/mL |
| mg/L creatinine | mg/mL = mg/L × 0.001 | 1000 mg/L = 1 mg/mL |
| g/L creatinine | mg/mL = g/L × 1 | 1 g/L = 1 mg/mL |
| µg/L THC-COOH | Same numeric value as ng/mL | 50 µg/L = 50 ng/mL |
Example THC-COOH / Creatinine Ratio Calculations
Example 1: Single sample
You have a urine THC-COOH value of 80 ng/mL and urine creatinine of 100 mg/dL.
Convert creatinine:
Calculate the normalized ratio:
The normalized THC-COOH/creatinine ratio is 80 ng/mg.
Example 2: Compare two samples
Sample 1 has THC-COOH of 120 ng/mL and creatinine of 150 mg/dL. Sample 2 has THC-COOH of 60 ng/mL and creatinine of 100 mg/dL.
Calculate Sample 1:
Calculate Sample 2:
Compare the two normalized values:
Sample 2 is 25% lower than Sample 1 after creatinine normalization.
FAQ
What does a THC-COOH/creatinine ratio mean?
It is a urine THC-COOH result adjusted for urine creatinine. Raw urine drug concentrations can change when urine is dilute or concentrated. Dividing THC-COOH by creatinine gives a normalized value in ng/mg, which can make serial results easier to compare.
Does a higher second ratio prove new cannabis use?
No. A rise or fall alone does not classify new versus residual use. Specialist serial models have population, timing and concentration restrictions. This calculator records the collection interval but does not apply such decision tables; ask the laboratory/MRO or clinician to interpret the results.
Why does low creatinine matter?
Low creatinine can mean the urine specimen is dilute. Dilution can lower the raw THC-COOH concentration and make results harder to interpret. Creatinine normalization helps adjust for this, but very low or very high creatinine still deserves caution.
