Work

P192 - ECE_1332 - Early changes in serum calcitonin during tirzepatide therapy in adults with obesity

Year: 2026

Type: conference-abstract

Abstract: Background Glucagon-like peptide-1 (GLP-1) receptor agonists have been associated with calcitonin elevation and C-cell hyperplasia in rodent models, raising concerns regarding thyroid safety. Human data, particularly for the dual GIP/GLP-1 receptor agonist tirzepatide, remain limited. This study aimed to evaluate the temporal pattern of serum calcitonin changes during tirzepatide therapy in adults with obesity and no known thyroid disease. Methods In this prospective observational study, 76 adults with obesity (mean age 48.7 ± 10.8 years; 73.7% female; mean BMI 40.6 ± 8.2 kg/m²) initiated tirzepatide for weight loss. Serum calcitonin was measured at baseline, 3 months, and 6 months using electrochemiluminescence immunoassay. Non-parametric paired analyses and linear mixed-effects models were applied due to skewed distributions. Secondary analyses assessed whether early calcitonin changes predicted subsequent elevations above predefined clinical thresholds (≥12 pg/mL). Weight loss outcomes were recorded to confirm treatment effectiveness. Results Median serum calcitonin increased modestly from 2.05 pg/mL (IQR 1.00-3.60) at baseline to 2.12 pg/mL (IQR 1.10-4.00) at 3 months and remained stable at 2.25 pg/mL (IQR 1.23-3.70) at 6 months (overall time effect, P < .001). The increase occurred early, with no further significant rise between 3 and 6 months (P = .43). Among participants with baseline calcitonin <12 pg/mL, two developed transient elevations above this threshold during early follow-up; no additional cases emerged at 6 months. Early change in calcitonin (baseline to 3 months) strongly correlated with 6-month change (ρ = 0.73, P < .001) and demonstrated excellent discriminatory ability for identifying individuals exceeding thresholds (AUC = 0.991). Tirzepatide therapy resulted in clinically meaningful weight loss (median −15.0% at 6 months). Conclusions Tirzepatide therapy is associated with an early, modest increase in serum calcitonin that does not progress with continued treatment over 6 months. Calcitonin elevations were infrequent, non-cumulative, and largely predictable from early changes. These findings support baseline and early follow-up calcitonin assessment, while suggesting that prolonged routine monitoring may not be necessary in patients without additional thyroid risk factors.

Source: European Journal of Endocrinology

DOI: 10.1093/ejendo/lvag096.368