Thyroid Research Thyroid Research Archive Thyroid Cancer

Undetectable serum thyroglobulin concentrations are strong evidence against recurrent thyroid cancer

(March 2007)

The background of the study. The presence of thyroglobulin in the serum of patients who have been treated for thyroid cancer indicates the presence of persistent or recurrent cancer. A rise in serum thyroglobulin after stimulation with thyrotropin (TSH) has proven to be a more sensitive test for the presence of persistent or recurrent thyroid cancer. In this study, a very sensitive assay for serum thyroglobulin was evaluated to determine whether basal measurements could supplant the need for measurements after TSH stimulation.

How the study was done. The main study subjects were 80 patients with thyroid cancer who had undetectable basal serum thyroglobulin concentrations. All had been treated by surgery and radioiodine, and none had evidence of recurrent cancer at the time of the study. All were taking thyroxine (T4), and their serum TSH concentrations were low.

After measurement of basal serum thyroglobulin, serum thyroglobulin was measured again after two injections of TSH. Serum thyroglobulin was measured using an immunoradiometric assay with a sensitivity of 0.1 ng/ml. The results in these 80 patients were compared with the results in 50 similar patients with basal serum thyroglobulin concentrations of 0.1 to 2.0 ng/ml.

The results of the study. Serum thyroglobulin concentrations after TSH administration in these 80 patients were <0.1 ng/ml in 59 percent, <2.0 ng/ml in 36 percent, and 1.0 to 3.0 ng/ml in 5 percent. In contrast, among 33 similar patients with basal serum thyroglobulin concentrations of 0.1 to 0.5 ng/ml, 24 percent had serum thyroglobulin concentrations >2.0 ng/ml after TSH stimulation, as did 82 percent of 17 patients with basal serum thyroglobulin concentrations of 0.6 to 2.0 ng/ml.

I-131 imaging and ultrasonography of the neck in 72 of these 80 patients (90 percent) revealed no abnormalities suggestive of recurrent carcinoma. (The results of these tests in the 50 patients with serum thyroglobulin concentrations of 0.1 to 2.0 ng/ml are not given.)

Follow-up TSH-stimulation testing and imaging in the patients with basal serum thyroglobulin concentrations <0.1 ng/ml revealed little change in serum thyroglobulin responses or no other evidence of recurrent carcinoma, except for one patient who had recurrent carcinoma in a cervical lymph node 1 year after initial testing.

The conclusions of the study. Patients with thyroid carcinoma who have undetectable serum thyroglobulin concentrations, as measured using a very sensitive assay, while taking T4, are at very low risk for recurrent carcinoma. Use of such a sensitive assay obviates the need for measurements of serum thyroglobulin after endogenous or exogenous TSH stimulation.

The original article. Smallridge RC, Meek SE, Morgan MA, Gates GS, Fox TP, Grebe S, Fatourechi V. Monitoring thyroglobulin in a sensitive immunoassay has comparable sensitivity to recombinant human TSH-stimulated thyroglobulin in follow-up of thyroid cancer patients. J Clin Endocrinol Metab 2007;92:82-87.