Endocrine Abstracts

Introduction: The current revised medullary thyroid carcinoma (MTC) guidelines don’t specify reference ranges of basal (bCT) or stimulated serum calcitonin (sCT) levels for the diagnosis of MTC. These are important for early diagnosis and correct management.

Objective: We aimed to set gender specific thresholds for bCT and sCT for MTC diagnosis.

Patients and methods: CT samples during calcium-stimulation test (25 mg/kgBW adapted on ideal body mass index) before and at 2, 5 and 10 minutes after administration were measured before thyroidectomy in 31 patients with thyroid nodules: 21 Females(F) – 10 Males(M), aged 47 y (23–67). bCT and sCT were compared with histological results. CT was measured by immunochemiluminescence.

Results: The test was well-tolerated, with minimum side-effects. For 8 patients with bCT<10 pg/ml (8F), the mean peak sCT was 106.6 pg/ml±197.12 (range:1.02–576). We identified 2 MTC, 1 papillary thyroid carcinoma (PTC) and 5-benign lesions. For 23 patients with bCT>10 pg/ml (13F–10M), the mean bCT and peak sCT were:28.49±26.9 pg/ml (range:11.57–104.4), respectively 356.35±206.07 pg/ml (range:98.1–724.6) in F, and 26.99±17.4 pg/ml (range:10.86–67.2), respectively 465.71±440.43 pg/ml (range:73.07–1571) in M. Histologically, we identified MTC in 6F and 1M, associated with C-cell hyperplasia (CCH) in 2 and with PTC in 3 cases. For the remaining cases, CCH in 1F and 2M; PTC in 4F and 3M; 1 follicular thyroid carcinoma in 1M and benign lesions in 2F and 3M. The best CT thresholds to discriminate normal cases from patients with either MTC or CCH were: 19.85 pg/ml for bCT (sensitivity – 66.7%; specificity- 89.5%), AUC 0.77 (CI:0.60–0.95), P=0.01, and 244.65 pg/ml for sCT (sensitivity – 75%; specificity – 63.2%), AUC 0.73 (CI:0.55–0.91), P=0.03. For F, the best thresholds to discriminate normal cases from patients with either MTC or CCH were: 13.15 pg/ml for bCT (sensitivity – 77.8%; specificity – 75%), AUC 0.82 (CI:0.64–1), P=0.01, and 208.2 pg/ml for sCT (sensitivity – 77.8%; specificity – 75%), AUC 0.78 (CI:0.58–0.98), P=0.02. Genetic results are awaited and other histopathologic evaluations are scheduled.

Conclusions: Our study found bCT and sCT cut-offs for discriminating MTC or CCH from normal subjects. The calcium gluconate test is well tolerated and safe to use. Larger studies are needed for accurate cut-offs that may improve diagnosis not only of MTC in early stages, but, interestingly enough, for PTC.