Relationship between serum thyroglobulin and 18FDG-PET/CT in 131I-negative differentiated thyroid carcinomas.

Abstract

The purpose of this study was to assess the relationship between [(18) F]-fluorodeoxyglucose ((18) FDG)-positron emission tomography/CT ((18) FDG-PET/CT) and serum thyroglobulin (Tg) in patients with recurrent differentiated thyroid carcinoma (DTC). Forty-two patients with recurrent DTC and negative Tg antibodies were included in the study. All patients underwent (131) I therapy due to an increasing serum Tg with a corresponding negative (131) I posttreatment whole body scan. The (18) FDG-PET/CT scans were then performed on all patients, serum Tg was measured concurrently, and respective results were compared. Sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV), and accuracy of the (18) FDG-PET/CT examination were 93%, 84%, 93%, 84%, and 90%, respectively. The sensitivity of (18) FDG-PET/CT significantly increased in patients with serum Tg levels ≥4.6 ng/mL (96%) in comparison with patients having lower levels (25%; p < .001). Nonetheless, 3 of 27 patients (11%) with a true-positive (18) FDG-PET/CT still had a Tg <4.6 ng/mL. Although (18) FDG-PET/CT scans are more likely to be positive with pretest Tg levels ≥4.6 ng/mL, 11% of patients with DTC with a lower serum Tg level will still have a positive scan. Our findings are in contrast with the American Thyroid Association (ATA) guidelines, which only recommend to perform (18) FDG-PET/CT in patients with Tg levels >10 ng/mL.