ADJUSTMENT OF DL(CO) FOR HEMOGLOBIN CONCENTRATION

The equation proposed by Cotes and coworkers is currently considered a s the most acceptable to correct carbon monoxide diffusing capacity (D L(CO)) for hemoglobin concentration [Hb] by both the American Thoracic Society (ATS) and the European Respiratory Society (ERS) guidelines f or standardization of DL(CO). In a previous study on 24 anemic patient s undergoing bone marrow transplantation (1), we found that DL(CO) is underestimated using the equation of Cotes and coworkers. To further e xplore this finding, 28 anemic patients ([Hb] = 8.2 +/- 1.0(SD)g/dl) w ith chronic renal failure were prospectively studied during the recove ry period of anemia (5.4 +/- 3.5 mo). In all 28 subjects, the slope De lta DL(CO)/Delta[Hb] computed as ratio of overall change in DL(CO) to overall change in [Hb] throughout the study period was 1.40 +/- 0.72 m i CO/min/mm Hg/g/dl. The individual relationship between measured DL(C O) and [Hb] closely fitted a simple linear regression. The resulting e quations for adjustment of DL(CO) (DL(CO)adj) to a standard [Hb] of 14 .6 g/dl for men and 13.4 g/dl for women are: DL(CO)adj (men) = DL(CO)o bs + 1.40(14.6 - [Hb]) DL(CO)adj (women) = DL(CO)obs + 1.40(13.4 - [Hb ]) The present adjustment function for DL(CO) is linear and independen t of the observed DL(CO) values, whereas the formulas previously propo sed are curvilinear, DL(CO) correction varying with the measured DL(CO ) values. For a measured DLCO of 15 mi CO/min/mm Hg and [Hb] ranging f rom 7 to 12 g/dl, the present DL(CO) adjustment is higher (by 2.7 mi C O/min/mm Hg, on average) than that proposed by Cotes and coworkers. Th is difference appears to be relevant for a precise interpretation of D L(CO) in patients with normocytic anemia in different clinical conditi ons.