Utility of C-terminal Telopeptide in Evaluating Levothyroxine Replacement Therapy-Induced Bone Loss

Levothyroxine (LT4) therapy has shown to have effects on bone metabolism though its deleterious effect on bone remodeling is debatable. This study was aimed at assessing the diagnostic utility of the bone remodeling marker C-terminal telopeptide (CTx) in detecting early bone loss.

In this case-control study, 84 premenopausal women of 30-45 years of age were selected. Out of them, 28 were recently diagnosed of hypothyroidism (not on LT4), 28 were on LT4 replacement therapy (100-200 μg/day) for more than five years, and 28 had euthyroid. Plasma CTx levels were estimated. Bone mineral density (BMD) was measured by quantitative ultrasound (QUS) method. Pearson's coefficient of correlation and ANOVA were used for statistical analysis.

CTx was most elevated in LT4-treated group (0.497 ± 0.209 ng/mL). It showed a significant negative correlation with T-score and Z-score of BMD values. In the treatment group of more than 150 μg/day, CTx showed significantly negative correlation with TSH (r = -0.462, P = 0.047).

LT4 therapy induces bone loss in hypothyroid patients. CTx levels can measure such bone loss along with BMD. Regular monitoring of CTx with adjustment in LT4 doses may help delay osteoporosis induced by prolonged LT4 replacement therapy.