Urinary loss of thyroid hormones: An issue to remember

Area of Science:

• Endocrinology
• Nephrology
• Internal Medicine

Background:

• Primary hypothyroidism requires careful management with levothyroxine.
• Nephrotic syndrome presents with significant proteinuria and fluid retention.
• Thyroid hormone transport proteins can be lost in urine during nephrotic syndrome.

Observation:

• A 45-year-old woman with hypothyroidism presented with elevated thyrotropin and low free thyroxine.
• She also exhibited nephrotic range proteinuria, leading to a lupus nephritis diagnosis.
• Generalized edema and very high cholesterol were noted.

Findings:

• The patient required increased levothyroxine dosage due to urinary losses of thyroid hormones.
• Lupus nephritis was identified as the underlying cause of nephrotic syndrome.
• Urinary loss of thyroid hormones is a critical, often overlooked, factor in managing hypothyroidism in nephrotic patients.

Implications:

• Clinicians should consider urinary thyroid hormone loss in patients with nephrotic syndrome and hypothyroidism.
• This phenomenon necessitates adjusted levothyroxine dosing for optimal thyroid hormone replacement.
• Early recognition and management can prevent complications associated with undertreated hypothyroidism.