Triglyceride Glycemic Index and Triglyceride/HDL Ratio: Can They be Biomarkers for Insulin Resistance in Euthyroid Women with Hashimoto's Thyroiditis, and Are They Related to Thyroid Function Tests?

INTRODUCTION: Hashimoto's thyroiditis [HT] is the most common autoimmune disease. Insulin resistance [IR], independent of thyroid function tests but attributed to thyroid autoantibodies, can be observed in HT. The most frequently employed method for demonstrating IR is the HOMA-IR index. Recently, the triglyceride-glucose index [TGI] and triglyceride-to-HDL ratio [TG/ HDL] have been proposed as novel, practical, and cost-effective indicators of IR. Thus, this study aimed to investigate the relationship between TGI, TG/HDL ratio, and HOMA-IR in euthyroid, normoglycemic women aged 18-45 years with HT. METHODS: This retrospective study was conducted at a tertiary care center and included 108 women with HT and 62 healthy controls. Parameters recorded for all participants included TSH, free thyroxine [fT4], free triiodothyronine [fT3], anti-thyroglobulin antibody [anti-Tg], anti-thyroid peroxidase antibody [anti-TPO], glucose, triglycerides, HDL, LDL, insulin, HOMA-IR, TGI, and TG/HDL ratio. RESULTS: Compared to the healthy control group, TGI and TG/HDL were significantly elevated in patients with HT, with respective values of 3.67 vs. 3.55 and 1.83 vs. 1.46 [p=0.001, p=0.005, respectively]. Anti-TPO showed a weak positive correlation with HOMA-IR and moderate positive correlations with TGI and TG/HDL [r=0.280, 0.352, and 0.336, respectively]. Similarly, anti-Tg correlated positively with HOMA-IR, TGI, and TG/HDL [r=0.274, 0.187, and 0.159, respectively]. A moderate, significant positive correlation was found between HOMAIR and both TGI and TG/HDL [r=0.477 and 0.455, respectively]. Receiver operating characteristic analysis indicated that TG/HDL [area under the curve [AUC]: 0.802, 95% confidence interval [CI]: 0.716-0.888, p<0.001] and TGI [AUC: 0.824, 95% CI: 0.741-0.907, p<0.001] had diagnostic value in predicting elevated HOMA-IR. Furthermore, a TG/HDL ratio of ≥1.99 predicted elevated HOMA-IR with 80.6% sensitivity and 70.1% specificity, while a TGI ≥ 3.68 had 87.1% sensitivity and 67.5% specificity. CONCLUSION: Women with euthyroid, normoglycemic HT exhibit increased HOMA-IR. TGI and TG/HDL are novel, cost-effective, accessible biomarkers that can be used to detect IR early in this patient group and facilitate screening across large populations.