Adjustment of DLCO for hemoglobin concentration.

Abstract

The equation proposed by Cotes and coworkers is currently considered as the most acceptable to correct carbon monoxide diffusing capacity (DLCO) for hemoglobin concentration [Hb] by both the American Thoracic Society (ATS) and the European Respiratory Society (ERS) guidelines for standardization of DLCO. In a previous study on 24 anemic patients undergoing bone marrow transplantation (1), we found that DLCO is underestimated using the equation of Cotes and coworkers. To further explore this finding, 28 anemic patients ([Hb] = 8.2 +/- 1.0 (SD) g/dl) with chronic renal failure were prospectively studied during the recovery period of anemia (5.4 +/- 3.5 mo). In all 28 subjects, the slope deltaDLCO/delta[Hb] computed as ratio of overall change in DLCO to overall change in [Hb] throughout the study period was 1.40 +/- 0.72 ml CO/min/mm Hg/g/dl. The individual relationship between measured DLCO and [Hb] closely fitted a simple linear regression. The resulting equations for adjustment of DLCO (DLCOadj) to a standard [Hb] of 14.6 g/dl for men and 13.4 g/dl for women are: [equations: see text]. The present adjustment function for DLCO is linear and independent of the observed DLCO values, whereas the formulas previously proposed are curvilinear, DLCO correction varying with the measured DLCO values. For a measured DLCO of 15 ml CO/min/mm Hg and [Hb] ranging from 7 to 12 g/dl, the present DLCO adjustment is higher (by 2.7 ml CO/min/mm Hg, on average) than that proposed by Cotes and coworkers. This difference appears to be relevant for a precise interpretation of DLCO in patients with normocytic anemia in different clinical conditions.