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

Objectives: To study iron metabolism and its association with thyroid function in infants with congenital hypothyroidism (CH). Study design: One hundred and twenty-three patients were recruited and matched with 110 controls. Serum levels of thyroid-stimulating hormone (TSH), thyroxine (T-4), free T-4 (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 T-4 were studied. Results: The CH group showed the following serum levels: SF=218.72 +/- 103.45 mu g/L, STfR=5.19 +/- 1.58 mg/L, STfR/lgSF=2.29 +/- 0.72 and T-4=38.39 +/- 19.11 nmol/L. The control group serum levels were: SF=182.44 +/- 96.17 mu g/L, STfR=4.39 +/- 1.70 mg/L, STfR/lgSF=2.03 +/- 0.83 and T-4=111.63 +/- 17.98 nmol/L. To adjust for an age mismatch between CH patients and controls, a subgroup analysis of all infants aged <= 28 days at blood sampling was performed and showed: SF=214.26 +/- 99.43 mu g/L, STfR=5.22 +/- 1.53 mg/L, STfR/lgSF=2.31 +/- 0.72 and T-4=36.90 +/- 17.11 nmol/L for CH patients and SF=188.50 +/- 98.30 mu g/L, STfR=4.56 +/- 1.72 mg/L, STfR/lgSF=2.10 +/- 0.87 and T-4=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 T-4 in CH patients only. Conclusions: 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.