Urinary loss of thyroid hormones: An issue to remember

Abstract

A 45-year-old woman suffering from primary hypothyroidism, previously well substituted with levothyroxine, was urgently referred from Primary Care to Endocrinology due to very elevated thyrotropin, free thyroxine at low limit of normality, very high cholesterol and generalised oedema. Hypothyroidism was suspected as the main aetiology of this clinical condition. A detailed examination showed nephrotic range proteinuria and the patient was finally diagnosed with lupus nephritis. Urinary loss of thyroid hormones, fundamentally linked to their transport proteins, in patients affected by nephrotic syndrome is sometimes a forgotten phenomenon and one which should be considered in patients with increased levothyroxine requirements. In this report, we present the details of this case and a brief review of the literature on this topic.

Keywords: Globulina fijadora de tiroxina (TBG); Hipotiroidismo; Hypothyroidism; Nephrotic syndrome; Proteinuria; Síndrome nefrótico; Thyroxin-binding globulin (TBG).