Emedinews:Insights on Medicolegal Issues:Failure to detect poison in chemical analysis by forensic lab

In some cases no trace of poison is found on analysis although from other circumstances it is quite certain that poison was the cause of illness or death. The possible explanations of a negative finding are:

• The poison may have been eliminated due to vomiting, stomach wash or diarrhea
• The whole of the poison may have disappeared from the lungs by evaporation or oxidation
• The poison after absorption may have been detoxified, conjugated and eliminated from the system
• Some drugs are rapidly metabolized, making extraction difficult.
• Some biological toxins and venoms, which are protein in nature cannot be separated from body tissues.
• Some organic poisons especially alkaloids may, by oxidation during life, or due to faulty preservation, or a long interval of time, or from decomposition of the body, deteriorate and cannot be detected.
• If the poison act slowly and death is delayed following production of irreversible organic changes, the poison may be completely metabolized and excreted.
• Many drugs may be present in very small amounts and these may require considerable amount of viscera for their identification.
• When the wrong or insufficient material has been sent for analysis.

Emedinews:Makesure:Reasons for false negative chemical analysis report of viscera

If the doctor conducting the autopsy has formed a conclusive opinion that the death is due to poisoning based on clinical evidence and after excluding other causes, he has all the authority to inform the investigating officer and mention his conclusive opinion in the postmortem report even if he is preserving the viscera for chemical analysis. A false negative test report may be due to: • Delay in chemical analysis • Improper preservation • Use of wrong analytical technique • Early disintegration of poison • Complete metabolism • Lack of suitable test for certain poison In accordance with a judicial pronouncement, the doctor who has conducted the postmortem examination can give his opinion as to the cause of death (due to poisoning) despite negative viscera report.

Emedinews:Insights on Medicolegal Issues:What are the viscera samples to be taken for chemical analysis by the doctor conducting the autopsy?

What are the viscera samples to be taken for chemical analysis by the doctor conducting the autopsy?

The majority of poisons are taken orally and the poison due to water content/liquids is likely to be present in the stomach and intestinal contents and their walls. After absorption all poison pass through the liver, which is the major detoxifying organ in the body and has the power of concentrating many poisons and making them identifiable when the blood and urine concentrations may have declined to very low levels. The kidney, being the organ of excretion, contains large amounts of poison, which is excreted into the urine. The following viscera are preserved in case of any suspected or evident case of death due to poisoning.

• Stomach and its contents. If the stomach is empty the wall should be preserved.
• Upper part of small intestine about 30 cm long with its contents
• Liver about 500 grams.
• One kidney or half of each kidney
• Brain in case of alcohol death
• Blood 100 ml/minimum 10 ml
• Urine 100 ml