Age-stratified association between AST/ALT ratio and all-cause mortality in asthma patients: a retrospective cohort study from the NHANES database

Asthma is strongly associated with metabolic diseases. Especially concerning liver disease, the correlation between the aspartate aminotransferase to alanine aminotransferase (AST/ALT) ratio, a marker of liver function, and the prognosis of asthma is not clearly defined. This retrospective cohort study, using data from the National Health and Nutrition Examination Survey (NHANES) 2001–2018, investigated the relationship between the AST/ALT ratio and all-cause mortality, with mortality follow-up completed through December 31, 2019. The association between the AST/ALT ratio and mortality was evaluated using Cox proportional hazards regression models. In addition, restricted cubic spline (RCS), subgroup analyses, and sensitivity analyses were employed to further elucidate the relationship between the AST/ALT ratio and mortality. The study ultimately included 2,137 people living with asthma with a median follow-up time of 8.83 years. After accounting for possible confounding variables, multivariate Cox regression analyses showed that the AST/ALT ratio was positively associated with the risk of all-cause mortality among people living with asthma (HR = 1.27, 95% CI: 1.09–1.65). Specifically, asthma patients in the highest quartile (Q4) had a significantly higher risk of all-cause mortality (HR = 1.68, 95% CI: 1.30–2.95) compared with the lowest quartile (Q1) of the AST/ALT ratio. In addition, the association between the AST/ALT ratio and the risk of death in people living with asthma varied across populations, and this association was more pronounced in people living with asthma older than 40 years (HR = 1.82, 95% CI: 1.51–2.27). Sensitivity analyses, including the exclusion of patients who died early in the follow-up period and those with cancer diagnosed during the follow-up period, confirmed the robustness of the results of the main analysis. In people living with asthma, the AST/ALT ratio was positively associated with the risk of all-cause mortality, and this association was more pronounced in those over 40 years of age. This finding highlights the significance of the liver index in predicting asthma prognosis.