Background: Thyroid function test is an essential tool in the diagnosis of thyroid dysfunction. To date, it is still controversial
which diagnostic algorithm is best applicable to clinically hyperthyroidism patients.
Objective: To compare various algorithms of thyroid function tests in the diagnosis of hyperthyroidism.
Method: Patients from the endocrine clinic, King Chulalongkorn Memorial Hospital were investigated for thyroid function tests (T3, T4, FT3, FT4 and TSH). Hyperthyroidism was defined as an elevated either FT3 or FT4 with suppressed TSH. The authors compared the effectiveness in hyperthyroidism diagnosis among algorithms by using sensitivity, specificity, positive predictive value and negative predictive value.
Results: Of all 452 patients in the present study, 94.24 percent were women. There were 206 hyperthyroidism, 30 subclinical hyperthyroidism, 1 subclinical hypothyroidism, 8 primary hypothyroidism and 207 normal subjects. The incidence of T3 toxicosis was 16.02% while that of T4 toxicosis was 2.16%. After the effectiveness analysis of these algorithms, FT3 and TSH is the most optimal test with 97.57% sensitivity and 100% specificity. Compared to FT4 and TSH, it gave 83.98% sensitivity and 100% specificity.
Conclusion: According to the high incidence of T3 toxicosis in the present study, FT3 and TSH should be the initial test for
diagnosis of hyperthyroid patients in an outpatient setting and FT4 should be measured subsequently in case of suspected
T4 toxicosis.

Keywords: Hyperthyroid, Thyroid function test, T3 toxicosis, T4 toxicosis