ObjectiveAlthough the TyG index is a reliable predictor of insulin resistance (IR) and cardiovascular disease, its effectiveness in predicting major adverse cardiac events in hospitalized acute coronary syndrome (ACS) patients has not been validated in large-scale studies. In this study, we aimed to explore the association between the TyG index and the occurrence of MACEs during hospitalization.MethodsWe recruited ACS patients from the CCC-ACS (Improving Cardiovascular Care in China-ACS) database and calculated the TyG index using the formula ln(fasting triglyceride [mg/dL] × fasting glucose [mg/dL]/2). These patients were classified into four groups based on quartiles of the TyG index. The primary endpoint was the occurrence of MACEs during hospitalization, encompassing all-cause mortality, cardiac arrest, myocardial infarction (MI), and stroke. We performed Cox proportional hazards regression analysis to clarify the correlation between the TyG index and the risk of in-hospital MACEs among patients diagnosed with ACS. Additionally, we explored this relationship across various subgroups.ResultsA total of 101,113 patients were ultimately included, and 2759 in-hospital MACEs were recorded, with 1554 (49.1%) cases of all-cause mortality, 601 (21.8%) cases of cardiac arrest, 251 (9.1%) cases of MI, and 353 (12.8%) cases of stroke. After adjusting for confounders, patients in TyG index quartile groups 3 and 4 showed increased risks of in-hospital MACEs compared to those in quartile group 1 [HR = 1.253, 95% CI 1.121–1.400 and HR = 1.604, 95% CI 1.437–1.791, respectively; p value for trend < 0.001], especially in patients with STEMI or renal insufficiency. Moreover, we found interactions between the TyG index and age, sex, diabetes status, renal insufficiency status, and previous PCI (all p values for interactions < 0.05).ConclusionsIn patients with ACS, the TyG index was an independent predictor of in-hospital MACEs. Special vigilance should be exercised in females, elderly individuals, and patients with renal insufficiency.