Pancytopenia of EPAS1^–/– mice responds to erythropoietin treatment. (A) Hematocrit levels for EPAS1^+/+ (□) compared with EPAS1^–/– (▪) littermate mice treated with erythropoietin (n = 4 per genotype per time point). The erythropoietin dosage was either low-dose (500 U/kg) for days 0 to 20 or high-dose (5000 U/kg) for days 21 to 30 of treatment. Statistically meaningful differences in means between the hematocrits of EPAS1^+/+ or EPAS1^–/– mice prior to initiation of erythropoietin treatment (one-tailed t test with P = .002) or after 10 days of low-dose erythropoietin treatment (one-tailed t test with P = .02) are indicated by an asterisk. No further differences between groups of mice were noted for all other time points (one-tailed t test with P > .1). (B) Complete blood cell count analyses for untreated EPAS1^+/+ (□) or EPAS1^–/– (▪) mice (n = 6 per genotype). Statistically meaningful differences in means between values from EPAS1^+/+ or EPAS1^–/– mice for white blood cells (WBCs; one-tailed t test with P = .0001), red blood cells (RBCs; one-tailed t test with P = .003), platelets (PLTs; one-tailed t test with P = .0018), or reticulocytes (RETs; one-tailed t test with P = .049) are indicated by an asterisk. (C) Complete blood cell count analyses for EPAS1^+/+ (□) or EPAS1^–/– (▪) littermate mice after erythropoietin treatment (n = 4 per genotype). Statistically meaningful differences in means between values of EPAS1^+/+ or EPAS1^–/– mice for platelets (one-tailed t test with P = .0001) or reticulocytes (one-tailed t test with P = .0005) are indicated by an asterisk. The units correspond to 10³/μL for WBCs, 10⁶/μL for RBCs, 10⁵/μL for PLTs, and 10⁵/μL for RETs. Values are expressed as the mean plus or minus standard error of the mean.