Borderline-low serum thyrotropin level is correlated with increased fasting urinary hydroxyproline excretion

Area of Science:

• Endocrinology
• Bone Metabolism
• Biochemistry

Background:

• Thyroid hormones significantly influence bone metabolism.
• Hyperthyroidism accelerates bone loss primarily through increased bone resorption.
• Subtle alterations in thyroid hormone status may impact bone turnover.

Purpose of the Study:

• To investigate the relationship between thyroid hormone status and bone turnover.
• To assess if fasting urinary total hydroxyproline-creatinine excretion (THP/Cr) can serve as a noninvasive marker for detecting changes in bone turnover related to thyroid status.

Main Methods:

• Retrospective analysis of ambulatory patients with thyroid function tests and THP/Cr measurements.
• Patients were categorized based on serum thyrotropin (TSH) levels.
• Correlation analysis between TSH levels, THP/Cr, and serum alkaline phosphatase.

Main Results:

• No correlation between TSH and THP/Cr was observed in patients with TSH > 1.0 mU/L.
• Patients with suppressed TSH (< 0.1 mU/L) showed elevated THP/Cr, consistent with hyperthyroidism.
• A significant negative correlation between TSH and THP/Cr was found in patients with TSH levels between 0.1 and 1.0 mU/L.
• THP/Cr positively correlated with serum alkaline phosphatase, indicating increased bone turnover.

Conclusions:

• Minimal excess of thyroid hormones, even within the low-normal or borderline range, is associated with increased bone turnover.
• These findings support the hypothesis that subtle thyroid hormone imbalances contribute to accelerated bone loss.
• Urinary THP/Cr is a sensitive marker for detecting thyroid hormone-induced changes in bone resorption.