A modification of the spectrophotometric determination of carbon monoxide in blood enabling direct determination of per cent hemoglobin saturation.

BECAUSE OF VARIATION in hemoglobin concentration in normal bloods with age and sex (1), the per cent carbon monoxide saturation of hemoglobin represents a more accurate toxicity index than the volume per cent of carbon monoxide. In 2 of the most common methods of carbon monoxide determination in blood, the gasometric method of Van Slyke (2, 3, 4) and the spectrophotometric method of Harper (5), the final results are obtained as volume per cent of carbon monoxide, necessitating a separate hemoglobin determination before the per cent carbon monoxide saturation can be computed. In the past this laboratory has used the cyanmethemoglobin method of Drabkin (6, 7) in conjunction with the spectrophotometric method for carbon monoxide to arrive at the per cent saturation. The principle of the spectrophotometric method for carbon monoxide involves preliminary treatment of a highly diluted blood sample with sodium dithionite, Na2S2O4, under which conditions carbon monoxide hemoglobin is unaffected and oxyhemoglobin is converted to reduced hemoglobin. If an excess of ferricyanide is then added, the reduced hemoglobin is converted instantly to methemoglobin, and the carbon monoxide hemoglobin is converted slowly over several minutes. A photometric measurement taken immediately after