Effects of chronic peritoneal dialysis on thyroid function tests

Peritoneal dialysis is associated with large losses of protein. In order to quantify thyroid hormone excretion in the dialysate and to examine the possibility that peritoneal dialysis may result in clinical hypothyroidism, nine endstage renal disease (ESRD) patients undergoing either continuous ambulatory peritoneal dialysis (CAPD) or chronic intermittent peritoneal dialysis (IPD) were studied. Total protein excretion in the peritoneal fluid was 21.5 +/- 2.1 g/24 h and did not vary with the mode of peritoneal dialysis. Thyroid binding globulin (TBG) excretion was 6.4 +/- 1.3 mg/24 h, higher than the values reported in the literature for urinary TBG excretion in patients with the nephrotic syndrome. Despite the higher TBG losses, serum TBG remained in the normal range. Mean peritoneal total T4 and T3 were 8.1 +/- 1.6 micrograms/24 h and 89.5 +/- 14.6 ng/24 h, and there was a significant correlation between peritoneal T4 and TBG (r = 0.69; P less than 0.01) and between peritoneal total proteins and T4 (r = 0.80; P less than 0.001). Despite the finding that large amounts of protein are lost in peritoneal fluid, T4 and T3 losses were relatively modest and remained below their daily production rates, and none of the patients were overtly hypothyroid. Serum thyroid stimulating hormone (TSH) was mildly elevated in three of nine patients and was consistent with early thyroid failure. The patients' serum iodine levels were higher than normal but did not predict the patients' thyroid status. We conclude that major protein losses could predispose patients undergoing CAPD to thyroid failure and that long-term follow-up of thyroid function is warranted in these patients.