Endocrine Abstracts (2006) 11 P835

On-levothyroxine measurement of thyroglobulin is not a reliable screening test for patients at high risk of remnant/recurrent differentiated thyroid carcinoma

Ali Gholamrezanezhad, Mohsen Saghari, Sahar Mirpour & Davoud Beiki

Tehran University of Medical sciences, Tehran, Iran.

At the present time, the most widely accepted tool for follow-up management of differentiated thyroid cancer (DTC) patients consists of serum thyroglobulin (Tg) measurement. It is not uncommon to measure the serum Tg level while the patient taking thyroid hormones (on-treatment Tg measurement). The purpose of the study was to evaluate the accuracy of on-treatment measurement of serum Tg in detecting remnant/recurrent or metastatic disease in high risk DTC patients. Patients and methods: We retrospectively analyzed the medical records of 26 high risk DTC patients and compare the on-treatment and off-treatment Tg levels of these patients. All patients were anti-Tg negative. Using off-treatment measurement of Tg as the gold standard, the results of on-treatment measurement of Tg in diagnosis of remnant/recurrent disease were analyzed for sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV). Results: The median serum Tg level under thyroid hormone suppressive therapy (on-treatment Tg) was 16.5 ng/ml and after withdrawal of thyroid hormone suppressive therapy (off-treatment Tg) was 95.0 ng/ml (P value=0.001). In 6 patients (23%) the on-treatment Tg level missed the recurrence of the disease. Regarding the off-treatment Tg as the gold standard, sensitivity, specificity, PPV and NPV of the on treatment Tg measurement was 72.7%, 100%, 100%, and 40%, respectively. Conclusion: Diagnostic Tg measurement without TSH-stimulation (on-treatment) is useless in the follow-up of DTC patients with high probability of residual/recurrent or metastatic disease.

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