Thyroid function in long term haemofiltration

Ten patients on haemofiltration treatment for between 4 and 20 months have been screened for thyroid function. Comparing serum T3 and T4 levels at the start of haemofiltration and 5 to 20 months later, a continuous decrease was detected (T3-Ria: 92 +/- 23 ng% to 68 +/- 23 ng%; T4-Ria: 4.94 +/- 1.79 microgram% to 3.81 +/- 1.21 microgram%). Serum TSH-Ria values also declined in mean from 3.48 +/- 0.47 muU/ml, yet two patients showed an increase as expected with a functioning hypothalamic pituitary-thyroid axis. During a single treatment TBG, T4 and T3 values increased in excess of the amount expected for the degree of blood volume contraction, whereas the T4/TBG ratio remained normal indicating peripheral euthyroidism. Serum TSH was found to decrease significantly after 5 hours of haemofiltration possibly by losses via the haemofiltrate. Stimulation of the pituitary gland by i.v. injection of 200 microgram TRH gave a normal TSH response. Chronic haemofiltration leads to a proportional decline of thyroid hormones and their protein bound fractions: euthryoidism was proved by the normal T4/TBG ratio and the absence of clinical signs of hypothyroidism.