Impact of methemoglobin on carboxyhemoglobin saturation measurement in fatal sodium nitrate and sodium nitrite cases.

This article focuses on the impact of nitrate- and nitrite-induced methemoglobinemia on the measurement of carboxyhemoglobin (COHb) saturation by spectrophotometric methods in forensic toxicology. It presents four suicide cases involving sodium nitrate or sodium nitrite ingestion, where elevated methemoglobin (MetHb) levels appeared to interfere with COHb measurements, potentially causing falsely elevated COHb saturation despite no carbon monoxide exposure. The authors suggest that high MetHb saturation may limit the reducing agent's ability to fully convert MetHb to deoxygenated hemoglobin, affecting spectrophotometric COHb results, and recommend using alternative methods such as gas chromatography for accurate COHb assessment in suspected methemoglobinemia cases. Further research is needed to clarify the relationship between MetHb saturation and COHb measurement accuracy postmortem.