Background: The 99mTcO4- thyroid scintigraphy is commonly used for hyperthyroidism diagnosis. Uptake value of 99mTcO4- on thyroid scintigraphy is an indicator of hyperthyroidism activity. Although, the correlation between free T3 value and free T4 value is not necessary clear in primary hyperthyroidism. Introduction: This study investigated the correlation between results of blood test and uptake of 99mTcO4- on thyroid scintigraphy in primary hyperthyroidism. Methodlogy: In this retrspective study, uptake was calculated in patients diagnosed with primary hyperthyroidism (Graves’ disease/Basedow’s disease) based on clinical findings, blood tests, thyroid ultrasound, and 99mTcO4- thyroid scintigraphy (uptake ≥3%) at St. Marianna University School of Medicine Hospital between 1 January 2010 and 31 December 2019. This uptake of 99mTcO4- was compared with results of blood tests. Results: Fifty-four consecutively arriving patients at the hospital (12 men, 42 women; mean age 43.0 ± 14.0 years) were selected. Free T3 (n = 54) was 14.6 ± 6.8 pg/mL, free T4 (n = 53) was 5.0 ± 2.3 ng/mL, and uptake on thyroid scintigraphy was 10.0% ± 7.1%. The correlation coefficients were 0.60 (p < 0.01) between free T4 (all case), 0.39 (p < 0.01) between free T4 (under 7 ng/mL), 0.12 (p = 0.70) between free T4 (above 7 ng/mL) and 99mTcO4-？thyroid scintigraphy uptake. Conclusion: In primary hyperthyroidism (Graves’ disease), there is a correlation between free T4 value and 99mTcO4- thyroid scintigraphy uptake, but there is no correlation in patients with high free T4 level.
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