Validation of a spectrophotometric method for quantification of carboxyhemoglobin

The measurement of carboxyhemoglobin (COHb) levels in blood is a valuable procedure to confirm exposure to carbon monoxide (CO) either for forensic or occupational matters. A previously described method using spectrophotometric readings at 420 and 432 nm after reduction of oxyhemoglobin (O₂Hb) and methemoglobin with sodium hydrosulfite solution leads to an exponential curve. This curve, used with pre-established factors, serves well for lower concentrations (1-7%) or for high concentrations (> 20%) but very rarely for both. The authors have observed that small variations on the previously described factors F1, F2, and F3, obtained from readings for 100% COHb and 100% O₂Hb, turn into significant changes in COHb% results and propose that these factors should be determined every time COHb is measured by reading CO and O₂ saturated samples. This practice leads to an increase in accuracy and precision.