GENDER DIFFERENCES IN INTRAVASCULAR VOLUMES VANISH IF EXPRESSED PER LEAN BODY MASS

Abstract BACKGROUND AND AIMS Blood volume (BV) is an important clinical parameter and is usually expressed relative to body weight (BW), but is inappropriate with elevated fat mass. We hypothesized that established differences in BV and hemoglobin mass (Hbmass) between male and female would vanish if expressed per lean body mass (LBM) instead of BW. We furthermore aimed to establish reference values for BV, plasma volume, red blood cell volume and Hbmass in women and men for clinical use. METHOD Blood volumes (carbon monoxide rebreathing) and body composition (DXA scan) were determined in 225 female and 280 healthy men (18–93 years, BMI range: 16.4–40.6). RESULTS As expected, female absolute BV was 1570 mL [CI 95% (1429.66–1709.87)]; P-value ≤.001) less than in male, and also when expressed per BW female had lower values than male (Figure 1A) [CI 95% (8.06–12.02); P-value ≤.001]. However, when expressed to LBM, females had 6.3 mL higher value than males [CI 95% (−8.80 to −3.86); P-value ≤ .001] (Figure 2A). In a similar manner, absolute Hbmass was 303 g greater in male [CI 95% = (283.99–322.09); P-value ≤ .001] and also greater when expressed pr BW [CI 95% (2.37–2.88); P-value ≤ .001] (Figure 1D). However, when normalized to LBM, differences were greatly diminished −0.84 [CI 95% (0.53–1.15); P-value ≤ .001] (Figure 2B). Per year of older age, a man gains 0.14 [0.06–0.22] mL blood/LBM (P = .0012) and a woman gains 0.13 [0.04–0.22] mL (P = .0032), but the increase in blood volume is not different between men and women (no interaction effect, P = .92). Similar observations as for BV and Hbmass were also made for red blood cell volume and plasma volume (See Figs. 1 and 2). CONCLUSION The principal finding is that when BV and Hbmass are expressed relative to LBM, the known differences in intravascular volumes and Hbmass between male and female largely disappear. Furthermore, the relation between LBM and intracvascular volumes and Hbmass is preserved with advancing age. Taken together, LBM is a very strong predictor for intravascular volumes and Hbmass in healthy humans and could be considered a valuable clinical matrix in medical care aiming to normalize intravascular volumes in patients such as chronic kidney failure and heart failure.