Summary
The aim of the present study was to investigate the effects of increased haemoglobin
(Hb) levels on the thyroid function in patients with β-thalassaemia major. Basal levels
of thyroid hormones (T4 , T3 ) and free thyroid hormones (fT4 , fT3 ), basal TSH concentrations and the TSH responses to a TRH bolus (0.2 mg iv) were
studied in ten euthyroid thalassaemic patients, aged 8 to 19 years, and in one 12
years-old thalassaemic girl with primary hypo thy roidism. Five euthyroid thalassaemic
patients (aged 8 to 12 years), as well as the hypothyroid thalassaemic girl, were
pre-pubertal, whereas five euthyroid thalassaemic patients (aged 15 to 19 years) had
delayed puberty. In each patient, the endocrine evaluation was carried out under conditions
of low Hb levels (31 days after the last blood transfusion, mean Hb = 9.8 ± 1.5 g/dl),
and 11 days after the transfusion of 2 units packed red blood cells (PRBC). The latter
increased significantly Hb concentrations in all the thalassaemic patients (mean Hb
= 12.8 ± 2.5 g/dl, P < 0.001). Twelve normal prepubertal subjects, aged 6 to 11 years,
served as the control group. Before the PRBC transfusion, basal T4 , 'T3 , fT4 , fT3 and TSH concentrations were similar in euthyroid prepubertal thalassaemic patients
(EPT) and in euthyroid patients with delayed puberty (EDPT), and were comparable to
those in control subjects. The TSH responses to TRH (TSH peak, area and ? area) observed
in EPT patients were similar to those in the EDPT group, but significantly higher
in comparison with the normal children. In EPT patients and in the prepubertal hypothyroid
girl the rise in Hb levels was associated with a significant increase in T3 and fT3 concentrations (T3 by 1.24-fold, P < 0.01; fT3 by 1.24-fold, P < 0.01), whereas no significant changes were found in EDPT subjects.
In both groups of euthyroid thalassaemic patients the PRBC transfusion did not alter
significantly basal T4 , fT4 and TSH levels and the TSH responses to TRH. An oxygen-induced improvement in the
peripheral mo-nodeiodinating system for T4 (iodothyronine 5'-deiodinase type I) could explain the rise in T3 and fT3 concentrations shown in prepubertal thalassaemic patients. In the EDPT group this
effect could be prevented by the tissue iron overload.
Key words
β-thalassaemia major - Thyroid function - TRH test - Haemoglobin levels