Space anemia unexplained: Red blood cells seem to be space-proof

Recently, an article with the title “Hemolysis contributes to anemia
during long-duration space flight” by Trudel et al. has been published
in Nature Medicine. The authors propose that accelerated hemolysis
of circulating red blood cells (RBCs) significantly contributes to “space
anemia.” After monitoring Hb-concentration [Hb] and exhaled carbon
monoxide (CO) in 14 astronauts during 5 months-long space missions
on the International Space Station (ISS), and up to one year after
return, they base this conclusion on an ≈11% decrease in [Hb]
between pre- and post-mission values, together with a ≈50% increase
in the rate of CO elimination, which was entirely ascribed to extravascular
hemolysis of RBCs. In our opinion, their interpretation is not
consistent with the data, and we believe that the term “anemia” is not
justified, because [Hb] was at most decreased to low-normal. We
propose here alternative explanations both for the low [Hb] and for
the elevation of exhaled CO, which, of course, require future experimental
proof.