Hypothyroidism and Nephrotic Syndrome: Why, When and How to Treat

Background: Hypothyroidism, characterised by low/normal free thyroxine (FT4) and free triiodothyronine (FT3) with elevated thyroid-stimulating hormone (TSH), is a well-known complication of nephrotic syndrome (NS). This is a common feature of primary and secondary glomerular diseases and comprises loss of protein in the urine and increased urinary excretion of thyroid hormones and thyroxine- binding globulin. With a normal thyroid reserve, this scenario is associated with the development of subclinical hypothyroidism, with a slight increase in TSH and normal free fractions. However, with a low thyroid reserve the transition toward overt hypothyroidism is almost inevitable, affecting morbidity and mortality. As T4 replacement is a cheap and well-established treatment to achieve a stable hormone status in different types of thyroid deficiency, it is essential to recognise and appropriately treat this condition. Conclusion: In this article we summarise the evidence on this nephro-endocrine disorder in humans and focus on diagnostic and therapeutic strategies.