Cerebrospinal fluid can provide useful additional evidence in postmortem GHB testing, particularly when urine is unavailable. A five-matrix autopsy study found generally lower GHB concentrations in cerebrospinal fluid than in peripheral blood. It did not establish that cerebrospinal fluid alone can prove or exclude ingestion.
The study and its collection conditions
Andresen-Streichert and colleagues examined a main series of 64 autopsies collected between January 2009 and November 2012. A forensic pathologist considered GHB exposure excluded as the cause of death. This classification was not independent proof that no person had ever ingested GHB.
The death-to-autopsy interval ranged from one to eleven days, averaging 4.8 days. Samples were analyzed on the collection day or immediately frozen at −20°C; the initial storage interval extended to 21 months in some cases. Peripheral venous blood, heart blood, urine, vitreous humor and cerebrospinal fluid were collected when available. The report’s ratio table identifies the peripheral comparator as femoral vein blood.
The actual matrix counts differed: 61 peripheral blood specimens, 56 heart blood, 50 urine, 54 vitreous and 52 cerebrospinal fluid. An unavailable specimen is missing information, not a negative result.
How cerebrospinal fluid compared
Cerebrospinal fluid GHB ranged from below 0.6 to 24.0 mg/L, with a mean of 4.2 and median of 3.2 mg/L. Forty-eight of 52 specimens were below 10 mg/L. Peripheral blood ranged from below 0.6 to 28.7 mg/L, with a mean of 11.9 and median of 10.6 mg/L.
Among 47 available cerebrospinal-fluid/peripheral-blood pairs, ratios ranged from 0.03 to 1.17, with a median of 0.37. The paper reported no statistically significant difference among the five specimen types overall. Lower descriptive averages therefore did not establish a significant matrix difference or create a fixed conversion factor. The correlation with peripheral blood was only moderate, r = 0.411.
Vitreous humor was not uniformly lower than blood: its range extended to 39.0 mg/L, and three of 54 vitreous specimens exceeded 30 mg/L. These findings explain why the authors favored obtaining more than one companion matrix where possible, rather than assuming every alternative specimen behaves alike.
What the analytical procedure could measure
The investigators quantified GHB by extraction, derivatization and GC–MS with GHB-d6 as internal standard. The detection limit was 0.5 mg/L and the quantification limit 0.6 mg/L. Calibration was linear from 1 to 100 mg/L. Reported inter- and intra-day accuracy was at least 91%, and imprecision no greater than 9% at the tested quality-control concentrations.
Recovery for cerebrospinal fluid and vitreous was approximately 19%, compared with approximately 30% in urine and serum. Recovery is an extraction characteristic, not the proportion of cases the test correctly classifies. Values below quantification were assigned zero for the study’s statistical calculations; that convention did not prove absence of GHB.
A conditional cutoff, not a diagnostic verdict
The authors proposed 30 mg/L for cerebrospinal fluid, urine and peripheral blood under the studied same-day-analysis or immediate-freezing conditions. They could not calculate diagnostic sensitivity or specificity from this cohort. A value below the proposed threshold is therefore not proof of no intake, and a value above it is not automatically proof of a fatal dose.
Ten additional cases with putrefaction were assessed separately. Their concentrations were not significantly higher overall than those in the main series; this small comparison did not establish that advanced decomposition is harmless. One advanced-putrefaction case had peripheral blood GHB of 32.7 mg/L.
Collection feasibility, specimen identity, handling and independent case evidence remain essential. A quantified concentration in cerebrospinal fluid does not establish impairment or cause of death. Compare the separate study of brain GHB and decomposition, which concerns a different tissue and different units.
Primary source
Andresen-Streichert H, Jensen P, Kietzerow J, et al. Endogenous gamma-hydroxybutyric acid (GHB) concentrations in post-mortem specimens and further recommendation for interpretative cut-offs. International Journal of Legal Medicine. 2015;129:57–68. doi:10.1007/s00414-014-1051-8.
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