Johansen K, Woodhouse N J
Department of Medicine, King Faisal Specialist Hospital & Research Centre, Kingdom of Saudi Arabia.
Eur J Med. 1992 Nov;1(7):403-6.
To compare serum thyroglobulin concentration and radioiodine scintigraphy during follow-up after thyroidectomy and radioiodine ablation for differentiated, non-medullary thyroid carcinoma.
One hundred fifty-eight patients received radiation ablation after thyroidectomy every 3-4 months until no pathological radioiodine uptake was seen on the scintigraphy. Simultaneously performed postablation scintigraphy and serum thyroglobulin measurement were related to clinical characteristics and mutually compared using kappa statistics (observed agreement not accounted for by chance divided by possible agreement not accounted for by chance).
After three ablation doses, serum thyroglobulin concentration had fallen to below detection limit (5 micrograms/L) in 71% of the patients and 70% of the patients had achieved negative scintigraphy after a median radioiodine dose of 3700 MBq I-131 and a median follow-up time of 5 months. The observed agreement between serum thyroglobulin and scintigraphy after the third ablation dose was 62%. The chance agreement was 50% giving a kappa value of only 24%. The size of the thyroid cancer at admission was larger in patients with a positive scintigraphy after first ablation compared with patients with a negative scintigraphy (p = 0.005) and was correlated to thyroglobulin concentration (p = 0.05). Among patients with thyroglobulin level > 5 micrograms/L after thyroidectomy and first ablation dose, there were more patients who at admission had palpable lymph nodes in the neck (p = 0.06) and microscopically verified neck metastasis (p = 0.03) compared with the group with thyroglobulin < 5 micrograms/L. These differences were not seen when comparing patients with positive and negative scintigraphies.
The low agreement between the two markers for thyroid cancer emphasizes the value of complementary use of thyroglobulin and scintigraphy in the follow-up of thyroid cancer patients. Patients with large tumours and neck metastasis probably need higher radioiodine doses for complete ablation.
