Endocrine Abstracts

Context: Hyperthyroidism is a common endocrine condition that can be associated with significant morbidity. It is important to ascertain the underlying cause of hyperthyroidism as the natural history, potential complications and response to treatment can be very different.

Objective: To investigate if measurement of TSH-receptor binding inhibitory immunoglobulin (TBII), a TSH-receptor antibody found in Graves disease, in the serum of newly diagnosed hyperthyroid patients is a satisfactory first-line test in finding the underlying cause.

Methods: Retrospective analysis of all patients with hyperthyroidism managed in the last 5 years was performed. All patients had serum thyroid function tests, technetium uptake scans, TBII and thyroid anti-microsomal antibodies, and thyroid ultrasound performed before treatment was commenced.

Results: Results for 309 patients were evaluated. TBII levels above 15 had a sensitivity of 86%, specificity of 95%, and positive predictive value of 97% and negative predictive value of 78% in diagnosing Graves’ disease. A lower TBII cut-off of 10 increased sensitivity but decreased specificity (90 and 87%, respectively) for diagnosing Graves’ disease. Other tests like anti-microsomal antibody, FT3/FT4 ratio, or thyroid ultrasound were much less sensitive and specific. Logistic regression analysis showed that TBII had by far the highest predictor for diagnosing Graves’ disease independent of age, gender, FT3/FT4 ratio and presence or absence of thyroid associated orbitopathy (Odds ratio (95% CI) of 61.7 (18.6–205)). Inclusion of results of technetium thyroid uptake scans in the equation showed that none of the variables remained significantly associated. Eight persons had raised TBII levels (>15) but non-uniform technetium uptake scans.

Conclusions: Measurement of TBII can be used as a first line test in the diagnostic pathway of hyperthyroidism. This could reduce costs and inconvenience in a significant majority of hyperthyroid patients. Only those patients whose TBII levels are ≤15 need further tests to find the underlying cause of hyperthyroidism.