Can QuEChERS GC–MS/MS Measure THC in Whole Blood Without Proving DUI? A 30-Case Validation

What Did the Researchers Actually Test?

The investigators developed and validated a way to extract three specified cannabinoids from whole blood before instrumental identification and quantitation. They optimized the extraction recipe, evaluated standard analytical-performance characteristics, and then applied the procedure to genuine specimens collected from 30 drivers who were suspected of driving under the influence of drugs. Those 30 drivers had initially returned positive cannabinoid results on the Dräger DrugTest 5000 oral-fluid screening device.

This was an analytical-method validation with an authentic casework application, not a controlled human dosing experiment. There was no randomized group receiving THC or placebo, no repeated observation of the same drivers during a known intoxication curve, and no independent measurement of lane keeping, reaction time, divided attention, or crash risk. The 30 casework specimens were collected in an already selected, screen-positive population. They cannot represent the sensitivity or specificity of the roadside screener in all drivers because no roadside screen-negative comparison cohort was tested.

Separate cannabinoid-negative volunteers supplied blank blood for method development and specificity assessment. The authors examined blank specimens from five volunteers for the absence of interfering target peaks. Those five blanks and the 30 suspected-driving specimens are different groups serving different purposes; a validation concentration level, a blood aliquot, and an individual person also are not interchangeable denominators.

Why Does the Whole-Blood Matrix Matter?

The original report concerns a physical sample of whole blood, with analyte quantities generally expressed as nanograms per gram (ng/g) of sampled material. Those units are mass per mass. They should not silently be relabeled ng/mL, converted to serum or plasma concentrations, or compared with a statute stated in a different specimen basis without verifying density, method, and legal definitions. Whole blood includes cellular components; serum and plasma are derived liquid fractions. They are not numerically interchangeable cannabinoid matrices.

The Dräger result was from oral fluid. It served as the reason cases entered the study, not the measured value reported in the whole-blood results table. Positive oral-fluid screening and mass-spectrometric quantitation in blood answer different questions. The former is a device-specific screening indication in saliva; the latter is an assay result for specified molecules in a subsequently collected blood specimen.

Anyone reviewing a result across specimens should keep the specimen, collection time, storage record, analyte, instrument, and reported unit attached to that particular result. The broader distinction is discussed in this site’s guide to biological matrices.

What Is QuEChERS, and Why Was It Used for THC?

QuEChERS is a family of sample-preparation approaches combining solvent extraction, salt-assisted partitioning, and a cleanup stage using a sorbent. Originally developed for analyzing residues in complex materials, the approach can be adapted for biological matrices, provided the analytes, matrix, and method are experimentally validated. It is not itself the detector that identifies THC. It prepares a sample so that the subsequent gas chromatograph and tandem mass spectrometer can measure the intended compounds.

In this experiment, salts influenced partitioning between water-rich blood and acetonitrile. The authors studied how changes in sodium chloride, magnesium sulfate, acetonitrile, C18 sorbent, and the amount of blood changed recovery. They observed that these variables did not have interchangeable effects across all three analytes. A recipe favorable for one molecule was not necessarily ideal for another.

The selected preparation used approximately 350 mg whole blood, 80 mg NaCl, 150 mg MgSO4, 650 µL acetonitrile, and 12.5 mg C18 sorbent. The extraction was followed by cleanup, evaporation, derivatization, and GC–MS/MS. Those values describe the study’s optimized laboratory procedure; they are not a template that proves a different laboratory’s method is validated merely because it also uses the word “QuEChERS.”

How Were THC and Its Metabolites Distinguished?

The three measured target compounds were parent THC, active metabolite 11-hydroxy-THC (11-OH-THC), and carboxy metabolite 11-nor-9-carboxy-THC (11-COOH-THC). These are separate molecular targets, not three names for a single cannabinoid concentration. Neither the detection of a metabolite nor the ratio among them proves the time of consumption in a particular person without additional, validated pharmacokinetic and case-specific information.

The team used separate deuterated analogues—THC-d3, 11-OH-THC-d3, and 11-COOH-THC-d3—as internal standards. This mattered because the extraction variables affected recovery differently for the three compounds. Isotopically labeled standards help account for processing and instrumental variation for their corresponding analytes; they do not establish that every conceivable interferent, specimen variation, or handling error has been excluded.

The final derivatized sample was evaluated using gas chromatography coupled to tandem mass spectrometry in multiple-reaction-monitoring mode. A target’s retention behavior and selected mass transitions provide more specific analytical information than an initial oral-fluid screening reaction. The overall evidentiary strength still depends on actual case calibrators, controls, acceptability criteria, and method validation, not the instrument label alone. See the site’s confirmatory drug-testing framework.

How Good Were the Reported Detection and Quantification Limits?

Table 2 of the primary paper gives distinctly different detection limits for the three blood analytes. The limit of detection (LOD) concerns whether a sufficiently small signal can be distinguished from background under the method’s criterion. The limit of quantification (LOQ) concerns when the method permits a quantitative report under the specified signal criterion. The investigators used signal-to-noise benchmarks of 3 and 10, respectively. These are method-defined analytical limits, not impairment cutoffs, criminal-law thresholds, or predictions about a particular person’s behavior.

These values refer to the investigators’ experimental preparation, calibration, and analysis. The precision measurements were evaluated using five independent spiked samples at a stated 25 ng/mL validation level, with intraday and three-day measurements; the table’s LOD and LOQ values are nevertheless reported in ng/g. The same paper reports calibration ranges that differ by analyte. High R² does not establish that a particular borderline result was quantified correctly if the sample fell outside the laboratory’s accepted reporting range or if a run-specific quality-control criterion failed.

What Did the 30 Authentic Driver Specimens Show?

All 30 specimens came from the already-screen-positive driving investigation group. The authors reported numerical whole-blood THC results for the individual cases, with substantial variation in the relative parent-drug and metabolite measurements. Rather than collapsing the cases into a single “cannabis level,” an evidentiary review should consider each analyte independently and preserve values below the method’s quantification limit as censored—not zero.

The following selections from the original case table illustrate analytically different profiles. They are examples, not a matched-time pharmacokinetic sequence; the authors did not administer identical doses to these drivers or establish each person’s exact consumption and sampling history.

The original report also discussed ten of the 30 people under a European legal framework cited by the authors. That is a historical, framework-dependent categorization, not evidence that the researchers directly observed impairment or established a current legal rule for every jurisdiction. It should not be recast as “ten demonstrably impaired drivers.” A legal classification, an analytical measurement, and a clinical assessment are separate propositions.

Can THC-to-Metabolite Patterns Date Cannabis Consumption?

Not precisely from this data alone. The authors discussed how comparatively large parent THC and smaller metabolite readings might be compatible with a shorter interval since use, and how some other profiles might suggest greater elapsed time. Such observations offer possible hypotheses, not uniquely determined individual timelines. Concentrations depend on route, dose, cannabis-use history, distribution and elimination, blood sampling time, analytical matrix, and the person’s biology. A single specimen seldom reveals those variables independently.

Even measured whole-blood analytes from the same person at one time cannot be translated into a unique smoking time merely by applying the population tendencies described in the paper. This research did not fit and prospectively validate a person-specific intake-time prediction model, report an uncertainty interval for such a prediction, or confirm suspected times against a controlled dosing record. In litigation, speculation about “recent use” should remain identified as an inference rather than promoted to a laboratory fact.

What Does a Positive Oral-Fluid Screen Add—or Fail to Add?

The initial oral-fluid result explains why the 30 cases were selected for blood testing. Because everyone entered after a positive roadside-type screen, the sample contains no representative screen-negative comparator group. It is therefore impossible to compute the screener’s false-positive rate, false-negative rate, sensitivity, specificity, or predictive value for the full driving population from these 30 selected cases alone.

Furthermore, the saliva screening result and laboratory blood quantitation were generated by different procedures and specimen types. They do not form two interchangeable measurements of the same instant in time. The original publication does not provide sufficient case-specific chronology to treat their values as a validated saliva-to-blood equation. A screening indication is an investigative lead; the confirmatory analyte measurement is a laboratory result. Neither, standing alone, supplies a filmed record of driving behavior.

What Do Accuracy, Precision, Recovery, and Matrix Effect Mean Here?

Accuracy concerns agreement with a known reference target under the study’s validation conditions. Precision describes repeatability or variability around those values. Recovery addresses how much analyte is captured through the extraction and cleanup process relative to the specified comparison procedure. Matrix effect refers to changes in analytical response attributable to the biological sample environment. Each is a separate property and none alone proves a result is beyond challenge.

The authors reported recoveries above 55% at the 25 ng/g fortified level under the chosen extraction conditions; that does not mean every analyte in every low-level forensic specimen was recovered at precisely 55%, or that a laboratory should “correct” a reported value by dividing by 0.55. The method used corresponding labeled standards to accommodate differing analyte behavior. The paper also reports no statistically significant difference between the calibration slopes in its particular matrix-effect comparison. That null finding is not a universal guarantee that hemolysis, unusual case materials, contamination, or other untested matrix interferences can never affect the procedure.

The method’s interday and intraday percentages likewise describe the validation design, not a probability that a named person’s reported THC value is medically correct or a statement of a forensic reporting uncertainty at a statutory threshold. Legal reporting of a numerical value requires the actual laboratory’s data, documentation of uncertainty where applicable, and the decision rule used for that case.

What Records Would Matter in a Disputed Blood-Cannabinoid Case?

A review should begin with the identity of the collected specimen and its continuity: collection site, time, containers, preservation details, seals, storage temperatures, receipt, aliquoting, and any reanalysis. The paper describes laboratory specimens that were stored at approximately −20°C before preparation, but its procedures do not prove a different jurisdiction’s collection kit or actual case storage complied with those conditions.

Then inspect the laboratory’s actual chromatograms, calibrations, blank and control records, identification transitions and retention tolerances, internal-standard responses, dilution or reinjection history, reporting thresholds, case-specific quality-review decisions, and the validated matrix and reportable range. Ask whether the laboratory genuinely used the same method and whether its validated scope included the case matrix, analyte, and concentration. A bibliography citation to this study cannot substitute for the performing laboratory’s own underlying records.

Specimen documentation, including tube choice and temperature chronology, should be analyzed separately from a conclusion about driving. The site’s specimen-collection guide identifies foundational evidence issues that may affect interpretation regardless of the instrumental method.

Does This Paper Establish a Legal THC Impairment Threshold?

No. Analytical method validation asks whether an instrument-based procedure can identify and measure specified compounds with characterized laboratory performance. Impairment is a functional proposition about the person at the relevant event. The original investigation did not measure lane control, reaction time, collision involvement caused by THC, or a complete cognitive examination of the 30 selected drivers. Nor did it compare the method with outcomes in a random or representative driver population at known doses.

The study therefore cannot validate a fixed whole-blood value as an individually reliable discriminator of safe and unsafe driving. Different legal systems use different rules for drug presence, concentration, and impairment; the historical European legal category noted in the article is not a free-standing finding applicable to every case. Even if a result meets a jurisdiction’s analytical or statutory criterion, separate analysis may be required to evaluate actual impairment, chronology, alternative explanations, and causation.

What Can an Expert Reliably Conclude From This Study?

Within its tested conditions, the experiment supports QuEChERS sample preparation followed by GC–MS/MS as a practicable method for quantifying three specified cannabinoids in whole blood, with analytical-performance characteristics that the investigators reported and an application to 30 authentic selected cases. It also demonstrates why a laboratory’s detailed method and separately optimized standards matter. The numerical case results exhibit real heterogeneity, a caution against reducing metabolite profiles to a single unqualified behavioral claim.

A careful forensic opinion should state the proposition in layers. First, what physical specimen was analyzed? Second, which individual molecule was identified and at what measurement level? Third, does the particular laboratory’s validation and case quality assurance support that value? Fourth, what additional evidence—medical records, behavior, chronology, body-camera video, witness observations, treatment or use history—addresses a claim of impairment or event causation? This source materially informs the first three layers but cannot independently answer the fourth.

It is particularly important not to translate a measured THC level into a blood-alcohol concentration, mistake a metabolite for parent THC, convert whole-blood mass units without validation, or treat all detected cannabinoids as equally psychoactive. Evidence sufficiency turns on the precise question asked, not the sophistication of the laboratory instrument’s name.

Frequently Asked Questions

Does this study show that GC–MS/MS is a reliable THC confirmation technique?

It supplies positive validation evidence for one specified GC–MS/MS method coupled to QuEChERS extraction in whole blood. Whether another laboratory’s case result is reliable requires that laboratory’s own validated scope, calibrators, controls, identification criteria, and actual case data.

Were the investigators measuring blood, breath, or saliva THC?

They quantified THC and two metabolites in whole blood. The oral-fluid DrugTest result was an entry condition for the 30 selected driving cases, not a quantitative blood concentration or breath measurement.

What is the reported THC quantification limit?

The original whole-blood method reported a THC LOQ of 0.033 ng/g and an LOD of 0.011 ng/g. The other two analytes had different LOQs. These method-specific limits do not constitute forensic impairment cutoffs.

Can a result below the LOQ be reported as zero?

No. Below-LOQ designates a result not quantitatively reportable under the stated criterion. It should not be invented as a numerical zero or treated as proof that the compound is biologically absent.

Were all 30 drivers proven impaired?

No. The sample consisted of 30 drivers suspected of drug-impaired driving after a positive oral-fluid screen. The authors documented chemical concentrations, not direct controlled performance tests establishing impairment for every participant.

Can the ratio between THC and 11-COOH-THC establish a smoking time?

Not from this single-sample method-validation study. The reported patterns may be used to consider hypotheses, but there was no controlled dose-time reference, individualized prediction equation, or validated timing confidence interval for those 30 cases.

Does the article validate a universal legal limit or prove collision causation?

No. Its purpose was analytical quantitation, and neither a universal driving-risk threshold nor a direct causal relationship between THC and a particular incident was established. Legal standards and case-specific functional evidence require separate examination.

Primary Research and Scope of the Conclusion

For the complete original experimental design, validation tables, 30 individual specimens, and limitations, consult Dybowski and Dawidowicz (2018), Forensic Toxicology, DOI 10.1007/s11419-018-0419-8. The evidence summarized here comes from that original investigation; analytical observations, historical legal classifications, and inferences about a particular person’s driving must remain distinct.