Analytical pit-holes in the determination of carboxyhemoglobin saturation in thermally denatured coagulated blood samples

Abstract

In the field of forensic toxicology, deaths related to carbon monoxide (CO) inhalation is one of the most relevant concerns. A common method for measuring CO-hemoglobin (Hb) saturation in blood is to measure the absorbance with a spectrophotometer. We recently encountered a fire case in which there appeared a large discrepancy between the autopsy findings and CO-Hb saturation, where the coagulated blood clots filling the heart and large blood vessels showed CO-Hb saturation of about 80% (CO poisoning level), but no soot was found in the bronchial tubes of the remaining body. We suspected this discrepancy to be caused by the application of spectrophotometry, which normally is applied to liquid blood sample, but in this case was applied to thermally coagulated blood. In this study, firstly we heated blood at various temperatures and times to investigate whether thermally coagulated blood clots were formed or not. Furthermore, CO-Hb saturation was measured in the coagulated blood clots using spectrophotometry to verify the discrepancy between the autopsy findings and CO-Hb saturation in the present case. The results show that CO-Hb saturation in coagulated blood clots that had undergone thermal denaturation and coagulation did not reflect the original values, in particular, blood samples with low CO-Hb saturation can show high CO-Hb saturation that may indicate CO poisoning. When determining cause of death, therefore, CO-Hb saturation value determined by spectrophotometer should be used with caution.