Can THC Be Lost During Oral-Fluid Analysis? What Synthetic Controls Reveal

THC handling losses can affect a laboratory’s oral-fluid controls, even when the analytical instrument performs precisely. Research using synthetic oral fluid shows why sample composition and storage belong in method validation.

A controlled matrix, not roadside donor samples

Gavrilović and colleagues fortified synthetic oral fluid with THC and several other drugs or metabolites. They evaluated a rapid dilute-and-inject LC–MS/MS procedure and tested stability under different temperatures and freeze–thaw conditions.

Synthetic material helps control variability during quality assurance. It does not reproduce every donor’s saliva, collection device, mouth contamination, or clinical condition.

Recovery and stability are separate questions

The investigators emphasized adding Tween 20 to reduce THC losses during handling. They reported good precision for the validated procedure and found that the fortified synthetic material could be stored at 5°C for up to a week without significant loss under their conditions.

That finding is specific to the matrix and procedure. A stable control does not establish that an unrelated authentic specimen, stored differently or in a different tube, remained unchanged. Likewise, repeatable results do not prove that analyte loss before measurement was absent.

Questions for a laboratory review

Identify the validated storage interval, container, additives, temperature record, and collection system. Determine whether controls experienced the same relevant handling steps as the case specimen and whether the method assessed THC separately from more stable analytes.

The study concerns analytical reliability. It does not provide a universal correction factor for an old sample or convert an oral-fluid concentration into impairment. Evidence of a possible loss mechanism should prompt a matched stability inquiry, rather than an assumed numerical adjustment.

The result also illustrates why a laboratory control and an authentic case specimen answer different questions. A control with a deliberately added surfactant may preserve a hydrophobic analyte differently from an untreated specimen. The relevant comparison is the actual validated handling procedure, rather than the fact that both materials are called oral fluid.

Related reading: limits of interpreting an oral-fluid THC result.

Primary research

Ivana Gavrilović; Alessandro Musenga; Kim Wolff; Alison Woffendin; Andrew Smart; Fan Gong; Duncan Harding; David Cowan. Stability of drugs of abuse in synthetic oral fluid investigated using a simple “dilute and inject” method of analysis. Drug Testing and Analysis (2022). DOI: 10.1002/dta.3279.