Clinical Utility of the Atherogenic Plasma Index for Identifying Atherogenic Dyslipidemia: A Large Cross-Sectional Analysis Stratified by Sex and Thyroid Status

BACKGROUND: The atherogenic plasma index (AIP) has emerged as a promising marker reflecting the balance between triglyceride (TG)-rich lipoproteins and high-density lipoprotein cholesterol (HDL-C). However, its clinical utility in identifying atherogenic dyslipidemia (AD), particularly across sex and thyroid function subgroups, remains incompletely characterized. OBJECTIVE: To compare the discriminatory performance of AIP and non-HDL-C for identifying AD in a large laboratory-based population, to evaluate this comparison across sex- and thyroid-status strata, and to explore thyroid-related and hematological patterns across AIP quartiles. METHODS: This laboratory-based cross-sectional study included 76.743 adult individuals with complete lipid, thyroid, and hematological parameters retrieved from preexisting routinely collected laboratory information system records. Participants were stratified into AIP quartiles. The primary analysis was the receiver operating characteristic-based comparison of AIP and non-HDL-C for identifying AD. Secondary analyses included AIP quartile group comparisons, Spearman correlation analysis, and exploratory multinomial logistic regression. RESULTS: AIP showed excellent discriminatory performance for identifying AD and outperformed non-HDL-C in the overall cohort (area under the curve 0.972 vs. 0.710). This stronger discriminatory performance was also observed across sex- and thyroid-status strata. Across AIP quartiles, lipid-related parameters showed the largest differences, particularly TG, HDL-C, and remnant cholesterol. Thyroid-related and hematological indices also differed across quartiles, but effect sizes were small. In exploratory multinomial regression models, age and male sex showed the most consistent associations with higher AIP quartile membership, whereas thyroid-related and hematological indices provided additional but limited explanatory information. CONCLUSIONS: AIP is a powerful and clinically practical marker for identifying AD, demonstrating superior and consistent performance compared with non-HDL-C across different clinical subgroups. Thyroid-related and hematological findings should be interpreted as exploratory rather than causal or biologically independent effects. Prospective multicenter studies are needed to validate generalizable AIP cutoff values and assess its added value beyond conventional lipid markers.