The importance of sample size with regard to the robustness of postmortem reference values

• Published in: Forensic science international Vol. 311; p. 110292
• Main Authors: Söderberg, C., Tillmar, A., Johansson, A., Wernvik, E., Jönsson, A.K., Druid, H.
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 01.06.2020; Elsevier Limited
• Subjects: Annan medicin och hälsovetenskap; Autopsies; Autopsy; Case management; Case-Control Studies; Diagnostic systems; Drugs; Female; Folkhälsovetenskap, global hälsa, socialmedicin och epidemiologi; Forensic pathology; Forensic sciences; Forensic Toxicology - methods; Humans; Hälsovetenskap; Intoxication; Laboratories; Male; Medicin och hälsovetenskap; Metabolism; Middle Aged; Pharmaceutical Preparations - blood; Pharmaceuticals; Postmortem Changes; Postmortem toxicology; Power; Reference concentrations; Reference Values; Rättsmedicin; Sample Size; Statistical methods; Substance Abuse Detection; Substance-Related Disorders - blood; Toxicology; Sweden; Reference concentrations; Sample size; Postmortem toxicology; Power
• ISSN: 0379-0738; 1872-6283; 1872-6283
• DOI: 10.1016/j.forsciint.2020.110292

•Postmortem reference concentrations are presented for 13 substances.•The study includes both intoxication subgroups and controls.•The impact of sample size on the reliability of the reference concentrations is investigated. Evaluating postmortem toxicological results is a challenging task due to multiple factors affecting blood concentrations after death. In order to improve the diagnostic accuracy in cases of suspected fatal intoxication different compilations of postmortem reference drug concentrations are often used. However, it is not clear what constitutes a reliable postmortem reference value. The current study presents reference concentrations for 13 substances from seven substance groups according to a standardized protocol. The reference concentrations were gathered from 3767 autopsy cases and subdivided into intoxications by one substance only (Group A, n=611), multi-substance intoxications (Group B, n=1355) and postmortem controls, in which incapacitation by drugs were excluded (Group C, n=1801). In particular, this study presents statistical information about the precision and conformity change with various sample sizes. Based on the present data >10 detections are usually needed, for the substances examined, to differentiate between intoxication cases and controls. Repeated samplings show that the median of small samples (N=≤5) has a high variation (normalized interquartile range 138–75%) and that a high number of detections (N=>20) in each group are needed to reduce the variation.