Cannabinoid Urine Extraction: Low Recovery Can Coexist With Accurate Calibration
A urine assay can have extraction recovery below 100% and still produce useful quantitative results when calibration and quality controls account for the process. Recovery, accuracy and sensitivity measure different aspects of analytical performance.
The method used a small urine volume
Researchers developed microextraction by packed sorbent, followed by gas chromatography–mass spectrometry, to measure THC, 11-hydroxy-THC, THC-COOH, CBD and cannabinol. The method required 250 microliters of urine and was tested with fortified specimens and seven authentic samples from cannabis consumers.
This was an analytical method-development study. It did not experimentally dose participants, establish a consumption timeline or compare urine concentrations with observed impairment.
Optimization did not affect every analyte equally
The investigators varied sample strokes, washing and elution. In the initial multivariable evaluation, the tested factors significantly affected THC-COOH recovery, while most other analytes did not show significant effects. Further response-surface optimization therefore focused on the major carboxy metabolite.
That finding illustrates why “a cannabinoid extraction” is not one uniform process. A condition chosen to improve one target may not be optimal for every other compound in the panel.
Recovery was not the final concentration error
The study compared pre-extraction and post-extraction spiking to estimate how much analyte survived preparation. Some recoveries were lower than those reported for other extraction techniques. Nevertheless, the validated workflow produced calibration and quality-control accuracy generally within the specified approximately 15% limits.
A low extraction yield does not automatically mean a patient’s reported result is underestimated by that same percentage. Standards processed through a comparable workflow and appropriate internal standards can account for reproducible losses. Conversely, inconsistent loss or an unrepresentative calibration matrix can compromise a result even if average recovery looks high.
Quantification limits were analyte-specific
The lower quantification limit was 1 ng/mL for THC and CBD, 5 ng/mL for cannabinol and 11-hydroxy-THC, and 10 ng/mL for THC-COOH. A single generic claim about the method’s “detection limit” would conceal these differences and confuse detection with reliable quantification.
The validation also examined carryover and stability under defined storage and processing conditions. Those findings do not certify arbitrary transport delays or every laboratory’s implementation.
When reviewing an actual urine result, request the analyte, preparation, calibration, quality controls and laboratory uncertainty. This paper supports a workable small-volume method; it does not provide a numerical shortcut from urinary metabolites to dose, exact last use or impairment.
Related analysis: Concentration Is Not Impairment: THC Blood Levels in California Driving Cases.
Primary research
Luana M. Rosendo and colleagues. The Determination of Cannabinoids in Urine Samples Using Microextraction by Packed Sorbent and Gas Chromatography-Mass Spectrometry. Molecules (2022). DOI: 10.3390/molecules27175503.
