Stability of postmortem methemoglobin: Artifactual changes caused by storage conditions

Area of Science:

• Forensic Science
• Hematology
• Toxicology

Background:

• Methemoglobinemia (MetHb) is a critical blood disorder where hemoglobin (Hb) is oxidized, impairing oxygen transport.
• MetHb levels can fluctuate post-mortem due to autoxidation, reductase activity, or microbial action, complicating its use as a diagnostic marker.
• Variations in blood state and storage conditions significantly impact MetHb measurements.

Purpose of the Study:

• To investigate the stability of post-mortem methemoglobin (MetHb) concentrations under various storage conditions.
• To establish reliable protocols for preserving MetHb integrity in forensic blood samples.
• To determine optimal storage methods based on post-mortem and analysis delays.

Main Methods:

• Blood samples were analyzed for MetHb concentrations after varying post-mortem delays and storage durations.
• Different storage conditions were tested, including refrigeration (4-6°C) with EDTA and freezing at -80°C or -196°C with cryoprotectant.
• MetHb levels were measured to assess the impact of storage duration and temperature on sample integrity.

Main Results:

• Post-mortem delay and analysis delay significantly affect MetHb concentrations.
• For delays up to two weeks, refrigeration of blood samples in EDTA (4-6°C) maintained MetHb stability.
• For delays exceeding two weeks, freezing blood samples at -80°C or -196°C with cryoprotectant was essential for preserving MetHb levels.

Conclusions:

• Minimizing post-mortem and analysis delays is crucial for accurate MetHb assessment.
• Refrigerated storage in EDTA is suitable for short-term (≤2 weeks) post-mortem sample preservation.
• Long-term ( >2 weeks) post-mortem sample storage requires freezing at ultra-low temperatures (-80°C or -196°C) to ensure MetHb stability.