HPX and hemolysis: During microgravity, hemolysis develops in astronauts, leading to anemia termed “space anemia” (Trudel et al., 2022); thus, plasma HPX levels will help assess not only the extent of anemia with other clinical parameters that include immune suppression (Wang et al., 2015) but also the restoration of normal hematopoiesis in astronauts and, potentially, space tourists upon their return to earth.