Validity of CO-oximetric determination of carboxyhaemoglobin in putrefying blood and body cavity fluid.

Most commercial CO-oximeters pose warning flags in their measured carboxyhaemoglobin (COHb) levels when total haemoglobin (tHb) concentrations in the samples are below a certain threshold, typically about 3-4gdl. The warning flags acknowledge the fact that the haemoglobin levels are outside the ranges these instruments are designed (or validated) for. By using a parallel GC method and special sample treatment methods prior to CO-oximetric measurements, this study demonstrates that CO-oximeters could actually produce valid COHb results for samples with tHb as low as 1g/dl, and that the warning flags have no bearing to the accuracy and precision of the measurements. This study also indicates that warning flags due to high methaemoglobin (MetHb) and sulphaemoglobin (SHb), and often turbidity did not affect the validity of the CO-oximetric measurements.

Sample pre-treatment for CO-oximetric determination of carboxyhaemoglobin in putrefied blood and cavity fluid.

Blood or blood-containing cavity fluid samples recovered from decomposed bodies in suspected carbon monoxide (CO) poisoning cases often have low total haemoglobin (tHb) levels or contain significant amounts of oily droplets, methaemoglobin (MetHb) and sulphaemoglobin (SHb), all conditions which render the validity of the measurements of carboxyhaemoglobin (HbCO) by commercially available CO-oximeters doubtful. Two sample pre-treatment methods, namely, centrifugal evaporation and addition of a commercially available standard haemoglobin solution containing a known level of HbCO, were developed to render such putrefied samples amenable to analysis by CO-oximeters. The methods developed were validated with samples of various degrees of putrefaction and various HbCO levels. The relative uncertainty of the determined HbCO levels as compared to their corresponding reference levels for the centrifugal evaporation method was approximately 5% and that for the standard addition method was <20%.