Low free thyroxine concentrations and deficient nocturnal surge of thyroid-stimulating hormone in haemodialysed patients compared with undialysed patients

Background. There is little information on the differences in pituitary-thy roid function between undialysed and haemodialysed patients. Methods. Serum concentrations of free thyroxine (T-4) and free triiodothyro nine (T-3), measured by enhanced chemiluminescence immunoassay, and thyroid -stimulating hormone (TSH) were compared in undialysed (n = 22) and haemodi alysed patients (n = 85). The response of the serum TSH concentration to ex ogenously administered thyrotropin-releasing hormone (TRH) and circadian va riation in serum TSH were also studied in the two groups. Results, Serum free T-4 concentration was significantly lower in haemodialy sed than in undialysed patients (1.02 +/- 0.02 vs 1.33 +/- 0.06 ng/dl, P < 0.0001). Serum concentrations of free T-3 and TSH were essentially the same for the two groups. The response of serum TSH concentration to TRH was bas ically the same. Serum TSH concentration in undialysed patients during the night and in the morning were 142.4 +/- 15.4% and 121.7 +/- 4.1% of that du ring the day, the differences being significantly different. A nocturnal su rge of TSH was not observed in haemodialysed patients. Conclusions. Low serum free T-4 concentration and a deficient nocturnal sur ge of TSH were found in haemodialysed patients compared with undialysed pat ients. The deficient nocturnal surge of TSH may contribute to the lower ser um free T-4 concentration in haemodialysed patients.