Study raises questions about anemia in astronauts

The changes observed in hematocrit during space flight were “striking,” according to the researchers. The mean hematocrit levels were:

• 40.9 ± 3.9 (range, 33.1–48.0) at baseline
• 45.9 ± 4.7 (range 38.2–52.1) at the early time point (P<0.05)
• 45.9 ± 5.5 (range 38.9–58.3) at the mid time point (P<0.05)
• 45.0 ± 2.5 (range 38.9–49.9) at the late time point (P<0.05).

Compared to pre-flight levels, hematocrit increased by 12.2% at early, 12.2% at mid, and 10.0% at late time points. In comparison, there was a 4.7% increase in hematocrit in reference samples from non-astronauts after the 48-hour processing delay.

Finally, the researchers found that platelet concentrations were elevated in flight, at the early and mid time points. However, platelets were not significantly elevated at the late time point, and they were stable upon landing.

For all of the astronauts, all blood parameters returned to pre-flight levels within 30 days of landing on Earth.

The researchers said these results are susceptible to the possible influence of dehydration or plasma volume alterations. However, the findings do suggest the increases observed in the ISS samples are partly due to a true in-flight increase in RBC count.

“Although the data does not indicate that significant anemia is present, it must be interpreted in the context of crew plasma volume during flight,” Dr Simpson said. “Overall plasma volume has been shown to be reduced during space flight, but this has not been assessed during long-duration missions.”

“In order to fully interpret the changes to RBC, hematocrit, and other parameters observed in this study, further research into plasma volume during long space missions is needed. This will be addressed in a separate, ongoing NASA investigation.”