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Pituitary-Thyroid Function in Chronic Renal Failure Assessed by a Highly Sensitive Thyrotropin Assay

Departments of Laboratory Medicine (M.J.H., S.S.R.) and Internal Medicine (L.N.), King Fahd Armed Forces Hospital Jeddah 21159, Saudi Arabia

Address all correspondence and requests for reprints to: Dr. Michael J. Hardy, Department of Laboratory Medicine, King Fahd Armed Forces Hospital, P.O. Box 9862, Jeddah 21159, Saudi Arabia.

Pituitary-thyroid function was assessed in 40 patients with chronic renal failure undergoing regular maintenance hemodialysis and in 35 normal subjects. Serum thyroid hormone levels were significantly lower in the dialysis patients than in the normal subjects (P < 0.001) and were in the hypothyroid range in a high proportion of dialysis patients (total T₃, 25%; free T₃, 45%; total T₄, 55%; free T₄) 45%; and free T₄ index, 38%). The reduced free thyroid hormone levels could not be explained by currently recognized assay artefacts. Serum TSH levels were higher than in the normal subjects (P < 0.01), but still within the normal range for most (35 of 40) dialysis patients and did not correlate significantly with total or free thyroid hormone concentrations in either group. These results suggest some impairment in the thyroidal response to TSH and impaired pituitary response to low serum thyroid hormone levels, the latter implying resetting of the normal feedback mechanism such that diminished thyroid hormone production evokes a smaller than normal increase in TSH secretion. This diminished thyrotroph sensitivity to reduced serum thyroid hormone levels may be beneficial in severe nonthyroidal illness.

Received March 4, 1987.