Fifty-Microliter THC Blood Testing: Sensitivity Does Not Validate Every Collection Method

forensic toxicology working group members October 28, 2026 Forensic Toxicology

A validated assay quantified THC using only 50 microliters of whole blood. That analytical achievement does not independently validate roadside finger-prick collection or establish the meaning of a very low result for impairment.

The sensitivity finding

Researchers developed liquid–liquid extraction and LC–MS/MS for six cannabinoids. The lower quantification limit for THC was 0.10 ng/mL. Limits differed for other targets, so one sensitivity figure should not be applied to the entire panel.

The method measured liquid whole blood. Its compatibility with microsampling volumes is distinct from demonstrating that every collection device, capillary specimen and storage procedure produces interchangeable results.

Small preparation changes affected different analytes

Alkalinization improved response for several cannabinoids but slightly reduced THC-COOH response. Protein precipitation also helped some compounds while reducing others. Optimizing parent THC therefore did not automatically optimize its metabolites.

Instrument equilibration mattered too: extending it stabilized response across repeated injections after an initially shorter interval produced signal loss. Repeated injections are tests of analytical consistency, not additional independent human subjects.

Surrogate calibration required examination

The investigators used horse blood for calibration and assessed performance in three sources of drug-free human blood. They examined accuracy, precision, interferences and matrix behavior rather than simply assuming equivalence.

That validation supports the stated laboratory workflow. A different laboratory still needs evidence covering its equipment, specimen handling and collection conditions. Very-low-concentration findings also require careful attention to blanks, contamination and uncertainty.

What a lower quantification limit changes

Greater sensitivity expands the range of exposures a laboratory can measure. It does not make the lowest quantifiable concentration a clinical or legal boundary.

The study supports a practical small-volume assay, not an automatic classification of recent use, impairment or causation. The specimen, analyte and method must be reported accurately before any further interpretation is attempted.

For context, see our discussion of THC concentrations and the separate question of impairment.