Elevated serum ferritin and soluble transferrin receptor in infants with congenital hypothyroidism.

To study iron metabolism and its association with thyroid function in infants with congenital hypothyroidism (CH). One hundred and twenty-three patients were recruited and matched with 110 controls. Serum levels of thyroid-stimulating hormone (TSH), thyroxine (T4), free T4 (FT4), ferritin (SF) and soluble transferrin receptor (STfR), were measured. The STfR/lgSF ratio (the serum transferrin receptor-ferritin index, TfR-F index) was calculated. Between-group differences in laboratory parameters and the correlation of parameters of iron metabolism with T4 were studied. The CH group showed the following serum levels: SF = 218.72 +/- 103.45 microg/L, STfR = 5.19 +/- 1.58 mg/L, STfR/lgSF = 2.29 +/- 0.72 and T4 = 38.39 +/- 19.11 nmol/L. The control group serum levels were: SF = 182.44 +/- 96.17 microg/L, STfR = 4.39 +/- 1.70 mg/L, STfR/lgSF = 2.03 +/- 0.83 and T4 = 111.63 +/- 17.98 nmol/L. To adjust for an age mismatch between CH patients and controls, a subgroup analysis of all infants aged < or = 28 days at blood sampling was performed and showed: SF = 214.26 +/- 99.43 microg/L, STfR = 5.22 +/- 1.53 mg/L, STfR/lgSF = 2.31 +/- 0.72 and T4 = 36.90 +/- 17.11 nmol/L for CH patients and SF = 188.50 +/- 98.30 microg/L, STfR = 4.56 +/- 1.72 mg/L, STfR/lgSF = 2.10 +/- 0.87 and T4 = 112.27 +/- 23.87 nmol/L for controls, respectively. STfR was significantly elevated in CH patients. Significant negative correlations were found for STfR and TfR-F index with T4 in CH patients only. Infants with CH did not show laboratory signs of iron deficiency. The observed elevation of STfR and its negative association with the severity of CH, suggest the presence of a self-regulating mechanism.