TG and Hashimoto thyroiditis: In addition, though ITA-PSV was not significantly correlated with serum F-T4 (ρ = 0.183, p = 0.414), F-T3 (ρ = 0.091, p = 0.687), or TSH (ρ = − 0.262, p = 0.239) in the present study, it was independently associated with an increase in LT4 dosage, suggesting that ITA-PSV reflects residual thyroid capability to increase thyroid hormone production, but not current thyroid hormone production capability, in patients with euthyroid or subclinical Hashimoto’s thyroiditis.