Isotopic renal function studies in severe hypothyroidism and after thyroid hormone replacement therapy

Area of Science:

• Nephrology
• Endocrinology
• Nuclear Medicine

Background:

• Thyroid hormones play a crucial role in regulating various physiological processes, including renal function.
• Severe hypothyroidism can lead to significant metabolic and hemodynamic changes, potentially affecting kidney function.

Purpose of the Study:

• To evaluate the impact of short-term, severe hypothyroidism on renal tubular function.
• To assess changes in renal function using technetium-99m mercaptoacetyltriglycine ((99m)Tc-MAG(3)) renography and compare with glomerular filtration rate (GFR).

Main Methods:

• A study involving 27 thyroidectomized patients assessed renal function before and after thyroid hormone replacement therapy.
• (99m)Tc-MAG(3) renography was performed to evaluate tubular function.
• Glomerular filtration rate was measured using (51)Cr-EDTA clearance, and serum creatinine levels were determined.

Main Results:

• Serum creatinine levels and (51)Cr-EDTA clearance indicated significantly reduced GFR in hypothyroid patients compared to post-treatment levels.
• No significant changes were observed in (99m)Tc-MAG(3) renography parameters, suggesting preserved tubular function.
• Renal hemodynamic changes in hypothyroidism primarily affect glomerular function.

Conclusions:

• Thyroid hormones do not appear to influence (99m)Tc-MAG(3) renography outcomes, indicating preserved renal tubular function in severe hypothyroidism.
• The observed reduction in GFR during hypothyroidism is mainly glomerular and appears reversible with hormone substitution.
• Caution is advised in managing patients with renal insufficiency and hypothyroidism.