By Stuart Kurtz, M.S. D-ABFT-FT
As discussed in the previous blog post, vitreous humor has many caveats when interpreting its results in the context of postmortem toxicology. For those considerations and some background on vitreous humor, check out that post first (https://axisfortox.com/vitreous-chemistries-pt1).
Vitreous humor can be used in instances where a drug or dug metabolite is quickly eliminated from the blood and it is known to cross into the vitreous and be detectable. One such metabolite is 6-acetylmorphine (6-AM) which is a marker for heroin exposure. Heroin is not typically looked for in blood samples because of its extremely short half-life at around 5-10 minutes. It metabolizes into 6-AM, which has a longer half-life at around 30 minutes, but it still may not be detectable in blood. Once 6-AM metabolizes into morphine, it is impossible to determine pharmaceutical morphine vs. heroin as the source. Urine would be the best matrix to look for the presence of 6-AM but vitreous humor is also a good option if urine isn’t available.
Electrolytes testing is one of the most common uses for vitreous humor. This usually includes sodium, potassium, chloride, glucose, urea nitrogen, and creatinine. Sodium and chloride concentrations in vitreous will approximate serum concentrations. Potassium concentrations will rapidly increase postmortem. Urea nitrogen and creatinine are similar to sodium and chloride in terms of correlation with serum concentrations and can be used as indicators for dehydration. Glucose concentrations in vitreous are more reliable than blood glucose concentrations prior to death. However, glucose vitreous concentrations dissipate rapidly in the postmortem interval. Therefore, although a diagnosis of hyperglycemia may be made from elevated vitreous glucose concentrations, a diagnosis of hypoglycemia cannot be made because of the time rate disappearance of glucose from the matrix. Postmortem blood glucose concentrations are considered unreliable and vitreous should be used when possible.
The significance of vitreous glucose is in helping to determine if diabetes played a part in cause of death. Elevated vitreous glucose is a good indicator that someone was experiencing a diabetic event. This can often be corroborated with acetone presence in the blood and/or vitreous humor. Additional testing for beta-hydroxybutyrate (BHB) can be done in blood if a diabetic event is suspected. Diabetes tends to not have any signs at autopsy so blood and vitreous testing can be helpful. BHB is the primary ketone that is produced during ketoacidosis. Diabetic ketoacidosis is typically associated with elevated glucose in vitreous humor. Medical history can also be very important if vitreous volume is limited or unobtainable.
The presence of acetone and normal glucose can be an indicator of some other form of ketoacidosis. Alcoholic ketoacidosis may occur in cases of binge drinking alcoholic beverages. As is typical with chronic alcoholism, the person will have evidence of liver disease. The underlying cause is malnourishment which can also occur independently of alcoholism. Malnourishment may also be associated with dehydration which would be indicated by elevated urea nitrogen, sodium, and chloride concentrations. Ultimately, diabetic vs. alcoholic vs. malnourishment ketoacidosis requires additional information beyond just the toxicology testing.
Medical history and an autopsy are very important for contextualizing the results we can provide for you in these cases. If your case potentially involves dehydration, it may be prudent to check the vitreous for sodium, potassium, or chloride, whereas if your case involves potential issues with diabetes or diabetic ketoacidosis, it would be necessary to order testing for vitreous chemistries to include glucose. If kidney function is a potential area of concern, evaluation of urea nitrogen and creatinine would be important. Again, as always in forensic toxicology, case circumstances and underlying pathology will aid in determining the best course of action when considering vitreous humor chemistry and electrolytes testing.
Please reach out to us if you have any questions regarding this topic or want help with deciding what testing may be necessary. Our email is [email protected] and our phone number is 317-759-4869 option 3.
Guidelines for the Interpretation of Analytical Toxicology Results. Disposition of Toxic Drugs and Chemicals in Man. Twelfth Edition. Randall C. Baselt. Biomedical Publications. Pages xxx-xlii. (2020).
Introduction to Forensic Toxicology. Clarke’s Analytical Forensic Toxicology. Sue Jickells and Adam Negrusz. Pharmaceutical Press. Pages 1-12. (2008).
Postmortem Toxicology. Clarke’s Analytical Forensic Toxicology. Sue Jickells and Adam Negrusz. Pharmaceutical Press. Pages 191-218. (2008).
Postmortem Forensic Toxicology. Principles of Forensic Toxicology. Fourth Edition. Barry Levine. AACC, Inc. Pages 3-14. (2017).