Red cell parameters in the circulation reflect the dynamic changes from the erythropoietic tissues. Red cell parameters were evaluated in C57BL/6 mice every day from P1 to P14 and then every week until 12 weeks of age using ADVIA 120. Hemoglobin (Hgb) (A), hematocrit (Hct) (B), RBCs (C), MCV (blue solid line) vs RDW (red solid line) (D), MCH (E), and measured mean cell hemoglobin concentration (CHCM) (F). n = 4-13 animals per day; data are presented as mean ± SEM. *P < .05, **P < .01, ***P < .001, ****P < .0001, indicated postnatal day vs P1 (ANOVA with Tukey’s post hoc test with corrections for multiple comparisons).