Postmortem Specimens

For postmortem analysis, ethanol is usually assayed in femoral blood, heart blood, bladder urine, vitreous humor, CSF (cisternal), bile, synovial fluid, brain, skeletal muscle, or liver (13). There could be other sources for postmortem ethanol. Many microorganisms are known to be responsible for ethanol formation in postmortem tissues, which is a frequent complication affecting interpretation of postmortem ethanol results. Candida albicans is most often reported to be responsible for ethanol formation in postmortem tissues using glucose as a substrate. C. albicans is located ubiquitously throughout the body particularly in the mouth and on the skin (14). Almost 100 different species of bacteria, yeast, and fungi have been reported to produce postmortem ethanol (15). Under optimal conditions, large quantities of ethanol can be generated by microorganism within hours of death thus complicating interpretation of ethanol levels in postmortem specimens. No significant increase in ethanol concentration was observed when postmortem specimens were homogenized in 1% sodium fluoride and stored at 4 or 25°C (16).

3.6.1. Biomarkers of Antemortem Ethanol Ingestion and Postmortem Ethanol Synthesis

To distinguish between antemortem ingestion and postmortem ethanol synthesis, several biomarkers of ethanol synthesis have been introduced. Nonoxidative Metabolites of Ethanol. Phosphatidylethanol and esters between ethanol and short-chain fatty acids have been recognized as markers of antemortem ethanol ingestion (16,17). These metabolites can be measured in blood using sensitive methods, such as GC-MS, and are excreted in urine with half-lives longer than ethanol (18). Serotonin Metabolites. Two urinary metabolites of serotonin, 5-hydroxy-tryptophol (5HTOL) and 5-hydroxyindoleacetic acid (5HIAA), have been investigated (19). These analytes can be measured using gas chromatography-mass spectrometry (GC-MS). A urinary ratio of 5HTOL/5HIAA > 15 suggests that ethanol has undergone metabolism, and a positive blood ethanol result stems from antemortem ingestion (19,20). Low-Molecular-Weight Volatiles. Microbial synthesis of ethanol from different substrates also yields other low-molecular-weight volatiles such as isopropanol, n-propanol, isoamyl alcohol, acetaldehyde, and propionic acid (21). Isobu-tyric acid and n-butanol have been proposed as reliable indicators of putrefaction, and if detected in blood, they indicate that blood ethanol result is uncertain (21). Ethyl Glucuronide. Minute amounts of ethyl glucuronide (EtG) are produced during enzymatic metabolism of ethanol. EtG can disclose recent drinking about 6-10 h after ethanol is no longer measurable (22). Meanwhile, EtG does not seem to be produced by yeast or bacteria from glucose. Therefore, if ethanol is produced in the body after death, no detectable EtG should be expected in the samples analyzed. EtG levels were found to decrease in urine specimens contaminated with Escherichia coli, probably because of cleavage by ^-glucuronidase (23). These bacterial actions can be stopped by adding sodium fluoride that prevents the formation of polysaccharides by the bacteria and prevents bacterial growth (22).

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