Pericardial fluid can support postmortem diazepam testing when peripheral blood is unavailable, but a strong correlation does not make the two specimens interchangeable. In a Norwegian study, 37 paired diazepam results had pericardial-fluid/peripheral-blood ratios from 0.30 to 7.3, despite a significant positive correlation between the matrices.
Which cases and specimens were compared?
Øiestad and colleagues collected six matrices during medicolegal autopsies from June 2013 through November 2016. Of 183 project cases, 109 had a benzodiazepine or z-hypnotic finding and entered this investigation. Not all 109 involved diazepam.
The matrices were peripheral blood, cardiac blood, pericardial fluid, psoas muscle, lateral vastus muscle and vitreous humor. Autopsies generally occurred within a week of death. After laboratory arrival, material was refrigerated at 4°C, typically for one to two weeks while peripheral-blood screening was completed.
Peripheral blood was femoral blood expressed after iliac-vein transection and cessation of initial flow. Collection often used both sides to obtain 40–50 mL. Thus, the blood reference was a specified postmortem collection, not a sample taken during life.
Preserve the paired result rather than dividing group medians
Table II reported diazepam concentrations above quantitation limits in 38 peripheral-blood samples and 40 pericardial-fluid samples. Their medians were 0.15 and 0.18 mg/L, respectively. These groups were not identical to the 37 pairs used for the ratio summary.
Table III gave a median paired pericardial/blood ratio of 1.7, with the range 0.30–7.3. Dividing the two concentration medians would produce a different number. It would not reproduce the median of individual paired ratios.
The Spearman correlation for pericardial fluid against peripheral blood was 0.81 and significant at the 0.01 level. This supports an association in the ordering of concentrations. It does not establish equal results, narrow individual prediction limits, or equivalence within a specified margin.
The relationship also depended on the compound
For parent clonazepam, 47 pericardial/blood pairs had a median ratio of 0.64 and range of 0.030–19. For 7-aminoclonazepam, the median was 1.1 across 62 pairs, with a range of 0.25–8.5. A general pericardial-fluid conversion factor would obscure these drug-specific patterns and individual outliers.
These are ratios between two postmortem measurements. They did not quantify how much either concentration changed after death, and no antemortem concentrations were available to identify which specimen best represented the level during life.
Analytical support did not eliminate biological variation
Routine screening and separate confirmation used UHPLC–MS/MS methods. The diazepam confirmation quantitation limit was 0.0071 mg/L. Results below the relevant limits were excluded from evaluation. All matrices used whole-blood calibration, with additional matrix-effect, recovery, accuracy and precision checks.
The authors described a deviating low-level diazepam QC sample affecting precision and accuracy in peripheral blood, cardiac blood and pericardial fluid. Analytical performance therefore belongs alongside the casework comparison rather than being assumed uniform across every result.
What can be concluded in a new death investigation?
Pericardial fluid is a useful alternative specimen, but its result should retain its own matrix identity and units. The study did not validate a lethal concentration, establish impairment or provide an exact missing-blood reconstruction.
For a different analytical question, see pericardial fluid versus urine for benzodiazepine screening. A screening comparison does not supply quantitative blood equivalence.
Primary source
Øiestad EL, Øiestad ÅML, Middelkoop G, Brochmann GW, Thaulow CH, Vindenes V. Comparative Study of Postmortem Concentrations of Benzodiazepines and Z-Hypnotics in Several Different Matrices. Journal of Analytical Toxicology. 2023;47:287–298. doi:10.1093/jat/bkac106.
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