Mean corpuscular hemoglobin concentration value, which is related to the hydration level (Gallagher, 2017) and/or internal viscosity (Williams and Morris, 1980) of RBC, was declined in ApoE/LDLR−/− mice compared to age-matched controls, what indicates lower RBC hydration, as an expected result of hypercholesterolemia (Prasad, 2010), except for 24-week-old female mice, where no significant change was observed. The gene discussed is LDLR; the disease is familial hypercholesterolemia.