Total body haemoglobin estimated with the alveolar CO method as compared with a 51Cr technique

Total body haemoglobin was estimated by the alveolar equilibrium CO method and by dilution of 51Cr-tagged erythrocytes in 22 patients with a wide range of haemoglobin concentrations (51-190 g/l). The resulting regression equation: THBCO =47 + 0.81 X THbCr, where THn is expressed in grams, shows that with increasing THb successively lower values were obtained with the THbCO method as compared with the THbCr method. Individual values were calculated for the M-factor, i.e. the ratio of the haemoglobin affinities to O2 and CO. These values were positively and significantly correlated to the red-cell content of 2.3-diphosphoglycerate. The findings are consistent with a recent hypothesis that the effect of 2.3-DPG on CO affinity may not be equivalent to its effect on oxygen affinity. The discrepancy between the two methods of estimating THb may therefore be apparent only and due to a systematic variation in the M-factor.