False-Positive Enzymatic Alcohol Results in Perimortem Specimens

A comparison between the enzymatic oxidation method and headspace gas chromatography with a flame ionization detector in the determination of postmortem blood ethanol

Ethanol is the most commonly encountered substance in forensic toxicology. Determining blood alcohol concentration (BAC) in autopsies accounts for the majority of work in forensic diagnosis. The most common method to assess BAC is the enzymatic oxidation method because of its low cost, easy operation, and high throughput. Still, the elevated lactate and lactate dehydrogenase (LDH) levels in postmortem blood may affect accuracy. This study uses headspace gas chromatography with a flame ionization detector (HS-GC/FID) to assess the interference of lactate and LDH levels on BAC in 110 autopsied blood samples determined by the enzymatic oxidation method. The results showed that lactate and LDH levels in postmortem blood were higher than in normal blood. There was a weak correlation between the lactate levels and BAC difference (r = 0.23, p < 0.05) and a strong correlation between LDH levels and BAC difference (r = 0.67, p < 0.001). The differentiation of BAC between the enzymatic oxidation method and HS-GC/FID was significant (p < 0.001), confirming the interference significantly. All postmortem blood samples with lactate and LDH levels higher than regular lead to a positive error in determining BAC by enzymatic oxidation method. The study results suggest that the HS-GC/FID method should be used to determine BAC in postmortem blood samples instead of the enzymatic oxidation method to avoid mistakes in forensic diagnosis.

Distribution ratios of ethanol and water between whole blood, plasma, serum, and erythrocytes: Recommendations for interpreting clinical laboratory results in a legal context

This article reviews the scientific literature dealing with the distribution of ethanol and water between whole blood (WB), plasma, serum, and erythrocytes (red-blood cells). Knowledge of the ethanol distribution ratio is important when analytical results derived from hospital clinical laboratories are interpreted in a forensic context, such as during the prosecution of traffic offenders. Statutory blood-alcohol concentration (BAC) limits for driving are defined as the concentration of ethanol in WB and not in plasma, serum or red-blood cells. These bio-fluids differ in their water content and thereby the concentrations of ethanol. Plasma and serum contain ~90%-92% w/w water, WB ~78%-80% w/w and erythrocytes ~64%-66% w/w. The mean plasma/WB and serum/WB distribution ratios of ethanol are therefore expected to be ~1.15:1 (91/79 = 1.15), which is in good agreement with values determined empirically. However, in individual cases, the actual distribution ratio will depend on the person's age, gender, and biochemical and hematological properties of the blood specimen, such as its hematocrit. For legal purposes, we recommend that the concentration of ethanol in plasma or serum determined at hospital laboratories is divided by a factor of 1.2, which would provide a conservative estimate of the co-existing BAC and the chance of overestimating the true value is only 1 in 2000 (0.05%).

False-Positive Ethanol Level in Urine and Plasma Samples of a Resuscitated Infant

We report the case of an 11-month-old male infant with a complex congenital heart disease who was admitted in the intensive care unit following cardiorespiratory arrest at home. Toxicological urine screening reported an ethanol concentration of 0.65 g/L using an enzymatic assay, without suspicion of alcohol intake; significant ethanol concentrations were found in two plasma samples using the same enzymatic assay. Plasma and urine ethanol concentrations were then below the limit of quantification when tested using a gas chromatography method. Urine ethanol level was also below the limit of quantification when tested by enzymatic assay after an initial urine ultrafiltration. These results confirmed our suspicion of matrix interference due to elevated lactate and lactate dehydrogenase levels interfering in the enzymatic assay. This analytical interference, well-known in postmortem samples, extensively studied in vitro, has been rarely reported in vivo, especially in children. To our knowledge, this case is only the sixth one reported in an infant's plasma and the first initially discovered from urine. Indeed, as for ethanol, this last matrix has not been studied in the context of this artifact which may induce false-positive ethanol results while seeking a diagnosis in life-threatening or fatal situations that are potentially subject to forensic scrutiny. In parallel to a synthetic literature review, we propose a simple, informative decision tree, in order to help health professionals suspecting a false-positive result when performing an ethanol assay.