Abstract
Objective The aim of this study was to define a cutoff serum thyroglobulin (Tg) level associated
with either residual or metastasis that may help decide postoperative radioactive
iodine (RAI) scan and treatment in differentiated thyroid cancer (DTC) patients residing
in low-income countries like Nepal.
Methods We prospectively studied a total of 81 patients (female-to-male ratio of 3.0:1; mean
age: 37.3 ± 14.0 years, within age range of 14–88 years) who underwent total thyroidectomy
with/without neck dissection and were referred for RAI whole-body scan (WBS) ± RAI
ablation or adjuvant treatment in the department of Nuclear Medicine, Chitwan Medical
College. We calculated the cutoff value of Tg using receiver operating characteristic
(ROC) curve analysis.
Results Forty-six of 81 patients (56.7%) had remnants in the thyroid bed, 26/81 (32.1%) had
regional lymph node metastasis, 9/81 (11.1%) had distant lymph node metastasis, 3/81
(3.7%) had lung metastases, and only 1/81 (1.2%) had bone metastases. RAI WBS was
positive in 61/81 (75.3%) patients and negative in 20/81 (24.7%) patients. Seventeen
of 81 (20.9%) patients had negative RAI scans with low serum Tg levels; only 3/81
(3.7%) patients had Tg elevated negative RAI scan (TENIS). Although scan was positive
in 61/81 (75.3%) patients, 64/81 (79.0%) patients received treatment with RAI, of
which 3/81 (3.7%) patients were TENIS patients. There was a significant difference
in serum Tg levels between patients who received or did not receive RAI ablation or
treatment (p < 0.05). On ROC curve analysis, the cutoff value of Tg levels between patients who
received and did not receive treatment was 2.9 ng/mL (sensitivity: 85.9%; specificity:
94.1%; positive predictive value [PPV], 98.2%; negative predictive value [NPV]: 64.0%;
AUC: 0.938).
Conclusion We identified a cutoff value of 2.9 ng/mL between patients who required or did not
require treatment with high sensitivity, specificity, and PPVs.
Keywords
thyroglobulin - radioiodine whole-body scintigraphy - differentiated thyroid cancer
- cutoff
