Oral Sodium Bicarbonate Improves Thyroid Function in Predialysis Chronic Kidney Disease

Abstract

Background/Aims: Metabolic acidosis (MA) in chronic kidney disease (CKD) associates with protein energy malnutrition, osteoporosis, abnormal endocrine function and increased mortality. Oral sodium bicarbonate has been shown to improve nutritional status and preserve renal function in CKD. Depressed thyroid function has been described in CKD and was believed to be related to MA. This is a prospective randomized study that examined the effect of oral sodium bicarbonate on thyroid function in predialysis CKD with MA. Methods: Predialysis CKD patients with serum total CO₂ ≤22 mM were randomized into two groups. The treatment group received increasing dose of oral sodium bicarbonate until serum total CO₂ was ≧24 mM. Control patients were kept on the same medications. Thyroid function tests were measured at baseline and again after 8–12 weeks. Results: All patients had a glomerular filtration rate <35 ml/min/1.73 m². Serum total CO₂ increased significantly in the treatment group and was unchanged in the control group. At baseline, over half of the patients had T3 below the lower limit of normal. At study completion, free T3 declined further in the control group, whereas free T3, total T3, free T4 and TSH rose significantly in the treatment group. Percentage changes of total CO₂ from baseline were strongly associated with the changes of T3 parameters. Glomerular filtration rate was maintained in the treatment group but declined significantly in the control group. Conclusion: Oral sodium bicarbonate, through correction of MA, improved thyroid function in predialysis CKD.