Pituitary-thyroidal function in children with β-thalassaemia major

Thyroid function was investigated in eleven β-thalassaemia major prepubertal children, 3–15 years old. Basal serum levels and the levels during a TRH-test of TSH, T4, T3, and rT3 were determined. The data were correlated with age and with serum ferritin levels. Although the patients were euthyroid clinically, the mean serum T3 and rT3 levels were significantly lower than the values in normal control children. Basal serum T4 and TSH values were similar to those of normal controls. In thalassaemic children, during the TRH-test, the increases in serum TSH at 20, 30, and 45 min, the peak and the maximum ΔTSH were higher than those normally found. Basal T3 and the 60 min value during the TRH-test were lower than normal, and the peak was delayed to 120 min. No statistically significant correlation was found between the hormonal parameters studied, and either chronological age or serum ferritin levels. That there is a slight impairment of thyroid secretion in thalassaemia major children is suggested only by the differences in response during the TRH-test (peak and maximum ΔTSH is increased, T3 increase delayed, the negative linear correlation between basal TSH values and per cent increase in T3 and maximum ΔT3, and the positive linear correlation between per cent increase in TSH and in T3). The low basal T3 and rT3 values might be explained by a decrease in the monodeiodinating enzymatic systems for T4, although other interpretations, e.g., increased clearance of T3 and rT3, cannot be excluded. The absence of clinical signs of hypothyroidism in thalassaemia major children might be due to the normal circulating levels of T4 if we accept that T4 has hormonal activity at least when T3 is low.