Relationships of serum free thyroxine and erythrocyte measures in euthyroid HFE C282Y homozygotes and control subjects: the HEIRS Study

Hemoglobin (Hb) levels and mean corpuscular volume (MCV) are abnormal in some persons with hemochromatosis or thyroid disorders. We sought to determine whether serum free thyroxine (T4) affects erythrocyte measures in euthyroid adults with or without C282Y homozygosity. We evaluated 488 white HFE C282Y homozygotes and controls (no HFE C282Y or H63D; normal serum iron measures) identified in screening; we excluded those with thyroid disorders, anemia, erythrocytosis, or serum ferritin (SF) <34 pmol/l. In the remaining 141 C282Y homozygotes and 243 controls, we evaluated correlations of log₁₀ free T4 with Hb, RBC, MCV, and red blood cell distribution width (RDW). C282Y homozygotes had lower mean age, higher mean Hb, MCV, and log₁₀ SF, and lower mean RBC and RDW than controls; mean log₁₀ free T4 did not differ significantly. In HFE C282Y homozygotes, there was no significant correlation of log₁₀ T4 with erythrocyte measures. In controls, there was a positive correlation of log₁₀ T4 with Hb (P = 0.0096) and a negative correlation with RDW (P = 0.0286). Among euthyroid white adults without iron deficiency, there are significant correlations of log₁₀ free T4 with Hb and RDW in controls, but not in HFE C282Y homozygotes.