Factors associated with TyG-BMI among pre-frail older adults: a cross-sectional study using multiple linear regression and decision tree analysis

TyG-BMI is a surrogate marker associated with insulin resistance and metabolic status. Characterizing its associated factors among pre-frail older adults may help describe metabolic variation in this population. Using baseline data from the 2015 China Health and Retirement Longitudinal Study, we conducted a cross-sectional analysis of 2249 adults aged ≥ 60 years classified as pre-frail. We aimed to examine factors associated with TyG-BMI using multiple linear regression and to explore subgroup patterns using classification and regression tree analysis. Univariate analyses and multiple linear regression (MLR) were used to examine associations between participant characteristics and TyG-BMI. CRT analysis was used to identify subgroups defined by combinations of demographic, residential, family, and social characteristics. For an exploratory discrimination analysis, participants were classified into high- and low-TyG-BMI groups according to the sample median, and receiver operating characteristic curves were used to evaluate discrimination between these groups. In the MLR model, weight, waist circumference, gender, and C-reactive protein were statistically associated with TyG-BMI. Weight had the largest positive standardized regression coefficient. The decision tree identified seven terminal subgroups, with gender as the root node and residence, number of living children, and social interaction appearing in subsequent splits. The PCOA-6 subgroup had the highest observed mean TyG-BMI (243.77), whereas the PCOA-2 subgroup had the lowest (194.92). The apparent area under the ROC curve was 0.873 (95% CI 0.859~0.888) for MLR and 0.605 (95% CI 0.582~0.629) for the decision tree. These AUC values describe discrimination between groups defined by the sample median and should not be interpreted as evidence of prediction of future clinical outcomes. This cross-sectional study characterizes factors associated with TyG-BMI and exploratory subgroup patterns among pre-frail older adults. Independent validation and longitudinal studies are needed to assess the reproducibility and clinical relevance of these findings.