Comparability of haemoglobin mass measured with different carbon monoxide-based rebreathing procedures and calculations

Background. Measurements of haemoglobin mass (Hb(mass)) with the carbon monoxide (CO) rebreathing method provide valuable information in the field of sports medicine, and have markedly increased during the last decade. However, several different approaches (as a combination of the rebreathing procedure and subsequent calculations) for measuring Hb(mass) are used, and routine measurements have indicated that the Hb(mass) differs substantially among various approaches. Therefore, the aim of this study was to compare the Hb(mass) of the seven most commonly used approaches, and then to provide conversion factors for an improved comparability of Hb(mass) measured with the different approaches. Methods. Seventeen subjects (healthy, recreationally active, male, age 27.1 +/- 1.8 y) completed 3 CO-rebreathing measurements in randomized order. One was based on the 12-min original procedure (COoriginal), and two were based on the 2-min optimized procedure (COnew). From these measurements Hb(mass) for seven approaches (COoriginalA-E; COnewA-B) was calculated. Results. Hb(mass) estimations differed among these approaches (p < 0.01). Hb(mass) averaged 960 +/- 133 g (COnewB), 981 +/- 136 g (COnewA), 989 +/- 130 g (COoriginalE), 993 +/- 126 g (COoriginalA,D), 1030 +/- 130 g (COoriginalB), and 1053 +/- 133 g (COoriginalC). Procedural variations had a minor influence on measured Hb(mass). Conclusions. The relevant discrepancies between the CO-rebreathing approaches originate mainly from different underlying calculations for Hb(mass). Provided Hb(mass) enabled the development of conversion factors to compare average Hb(mass) values measured with different CO-rebreathing approaches. These factors can be used to develop reasonable Hb(mass) reference ranges for both clinical and athletic purposes.