Prognostic value of postoperative and post-ablative serum thyroglobulin levels in patients with differentiated thyroid cancer.

Background: The study was designed to examine the value of post-operative and post-ablative serum thyroglobulin levels and diagnostic whole body scan in predicting remission in patients with differentiated thyroid carcinoma.

Methodology: Serum TG levels and diagnostic iodine-123 whole body scans performed prior to and 6-12 months after 131I ablation for DTC were evaluated in 100 consecutive patients at King Faisal Specialist Hospital Riyadh. Patients were followed up for a period of 7.6 years (range 7-10 years). All patients underwent total thyroidectomypriorto 131I ablation.

Results: Patients with serum TG levels < 8 ng/ml post thyroidectomy (50 patients) also maintained low TG < 8 ng/ml after 131I ablation and had better outcome (60%) remission. On the other hand DTC subjects with higher TG > 8 ng/ml post thyroidectomy (50 patients) 40% remained in remission X2 = 4.00, p = 0.046. For the group with initial high post-operative TG, it became < 8 ng/ml in 34/50 (68%) patients after ablation with 131I and in this subgroup, remission was seen in 16/34 (47%) of patients in contrast to 4/16 (25%) remission rate in those who continue to have TG > 8 ng/ml after ablation. At the end of follow up, 123I-WBS was positive in 4% and 10% of patients with initial TG < 8 ng/ml and TG > 8 ng/ml respectively; X2 = 1.38, p= 0.24.

Conclusion: Post-operative and post-ablative serum TG levels -but not follow up diagnostic WBS- have predictive values and permit selection of patients with higher risk for persistent/recurrent disease.