A urine GHB result above a proposed postmortem cutoff can support investigating exposure without establishing the GHB concentration in blood at death. Loos and colleagues described two cases with urine concentrations of 35 and 72 mg/L, while femoral blood was below 10 mg/L in both. Those paired findings cannot be reduced to one positive-or-negative answer about fatal intoxication.
What the two cases actually involved
The 2023 report described two men found dead after circumstances involving several drugs. Femoral blood and urine were collected at the scene during external examinations. Neither case underwent a forensic autopsy. The authors discussed them as fatal mixed intoxications, but the report is not a controlled study identifying the independent contribution of GHB.
In the first case, drug-taking circumstances and materials including GBL were reported. Urine GHB measured 35 mg/L and femoral blood was below 10 mg/L. Other substances were detected in the investigation. The estimated postmortem interval was approximately six hours; that estimate should not be treated as a precise death-to-collection timestamp.
In the second case, the history included MDMA and GHB use, subsequent illness and tramadol ingestion. Urine GHB measured 72 mg/L and femoral blood was again below 10 mg/L. The reported postmortem interval was approximately two hours. Multiple other substances were detected, and ethanol measured 1.6 g/L in blood and 2.3 g/L in urine. The different units for ethanol and GHB must remain explicit.
Screening and quantitative GHB testing were different steps
The investigation included on-site drug screening, immunochemical urine testing and blood drug screening by liquid chromatography with mass-spectrometric detection. Class-based immunochemical findings should not be upgraded to confirmed identification or quantitation of every individual drug.
GHB itself was measured using a chromatographic procedure described as GC–FID, involving conversion to gamma-butyrolactone in acid and a gamma-valerolactone internal standard. Thus, the numerical GHB findings were not simply positive immunoassay results. The article described the method as validated but did not provide numerical detection limits, quantification limits, precision or uncertainty for these case results. “Below 10 mg/L” should not be rewritten as zero.
Why urine and blood answer different questions
The authors used a proposed urine interpretive cutoff of 30 mg/L to flag possible exogenous exposure. Both urine results exceeded it. The paired blood results provided different information and did not demonstrate a high circulating GHB concentration in either specimen at collection.
This discordance does not establish that one matrix was analytically wrong. Nor does it permit a back-calculation from urine to blood at death. The report discusses rapid elimination during life and postmortem formation as interpretive problems, but it did not measure serial antemortem concentrations or experimentally partition those mechanisms in either case.
Storage recommendations in the discussion are also not equivalent to a complete documented handling history for each case specimen. Freezing after collection cannot retrospectively remove GHB that formed before collection.
What the cases support in practice
A review should retain both matrix-specific numbers, the collection circumstances, estimated interval, analytical method and evidence of exposure. It should distinguish the authors’ interpretation of the deaths from what the measured GHB concentrations alone establish. Two selected cases cannot validate a cutoff’s sensitivity, specificity or ability to diagnose fatal intoxication.
For a complementary collection-site problem, see cardiac blood GHB above 50 mg/L. Neither a high cardiac value nor a urine result should independently establish impairment or cause of death.
Primary source
Loos NHC, van den Hondel KE, Reijnders UJL, Franssen EJF. Complications in post-mortem GHB cut-off values in urine samples: A case report. Toxicology Reports. 2023;10:600–603. doi:10.1016/j.toxrep.2023.05.002.
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