RAPID CHANGES IN THYROID-FUNCTION TESTS UPON TREATMENT OF TUBERCULOSIS

Setting: Inpatient service and tuberculosis (TB) clinic of a public ho spital. Objectives: (1) To test the hypothesis that an hepatic effect of antituberculosis drugs increases serum thyroxine-binding globulin ( TBG); (2) to resolve conflicting reports on thyroid function in TB. De sign: Measurement of serum thyroid hormones, thyroid hormone binding ( T3RU) and binding proteins (TBG, transthyretin [TTR] and albumin) in 3 8 patients with active TB and in 29 healthy tuberculin-positive contro l, before and about 10 days into therapy. Results: With therapy of TB (with isoniazid [INH], rifampin [RIF], ethambutol and/or pyrazinamide) , TBG increased above control values and T3RU decreased (P < 0.001). T hese changes were weakly correlated with liver enzyme activities but d id not predict clinical hepatitis, which developed in only 1 patient. T3 was initially subnormal in 61% of 38 TB patients, while T4, thyrotr opin (TSH) and TBG were normal. T3, TTR and albumin, all negative acut e phase reactants, increased towards normal by day 10 (P < 0.001). Thy roid function remained unaltered in 14 control patients taking INH, wh ereas T3RU decreased (binding increased) and T3 increased in 15 taking INH and RIF (P < 0.001). Conclusions: TB patients manifest the expect ed low T3 of non-thyroid illness, but, unlike most sick patients, usua lly have normal or increased serum binding of thyroid hormones. Chemot herapy further increases binding by increasing TBG, an effect probably due to RIF.