Stat5a^−/−5b^−/−-mice with near-normal hematocrit have a sluggish response to erythropoietic stress.

Six adult Stat5a^−/−5b^−/− mice with initial hematocrit more than 35% and 6 wild-type controls were injected with phenylhydrazine on days 0, 1, and 3 (indicated by small arrows). The corrected reticulocyte count (also known as reticulocyte index21) allows an assessment of erythropoietic rate, and was calculated assuming a normal hematocrit of 45%, as follows: Corrected reticulocyte count (%) = reticulocyte count (%) × (hematocrit/45).