Thoracic cavity fluid as an alternative specimen for carboxyhaemoglobin measurement in post-mortem toxicology

Post-mortem blood is most frequently used for the measurement of carboxyhaemoglobin (COHb) in post-mortem forensic cases, when investigating suspected inhalation of carbon monoxide (CO). However, in many post-mortem cases (especially severe burns and charring deaths), adequate blood specimens are not always available for toxicological analyses. Here, the availability of an alternative specimen for COHb analysis is required. This study investigated the suitability of thoracic cavity fluid (TCF) as an alternative specimen for the measurement of COHb. TCF and comparative blood samples from fifteen potential CO toxicity cases were collected into green-top tubes (containing lithium heparin) and analysed immediately after collection using a validated method on the ABL825 FLEX Radiometer CO-oximeter. Pearson's correlation coefficient indicated a strong positive relationship between the two specimens (r = 0.975, n = 10, p < 0.001). A statistical agreement between COHb concentrations from blood and TCF was demonstrated using the Bland-Altman plot, with a slight bias of 1.54 % when blood was taken as the standard. This study found that TCF would be a suitable alternative to blood for the measurement of COHb using the ABL825 FLEX blood gas analyser.