Nonlinear Association Between Atherogenic Index of Plasma and Unstable Carotid Plaque: A Single-Center Retrospective Study

Background: The atherogenic index of plasma (AIP) is a marker of lipids and atherosclerosis. However, the association between the AIP and the risk of unstable carotid plaque remains unclear. Methods: A total of 10,732 patients were enrolled. Carotid ultrasound was used to assess the stability of carotid plaque. The AIP was calculated using the formula AIP = log (TG/HDL-C). Logistic regression was used to investigate the association between the AIP and unstable carotid plaque. The nonlinear association between the AIP and unstable carotid plaque was analyzed using restricted cubic splines (RCSs), and a two-segment logistic regression risk model was constructed for both sides of the inflection point. Results: Of the total number of patients, 7834 had stable carotid plaque and 2898 had unstable carotid plaque. Our findings demonstrated an inverted U-shaped association between the AIP and the risk of unstable carotid plaque (threshold = 0.10). When the AIP was <0.10, a significant positive association with unstable carotid plaque emerged (OR: 1.24, 95% CI: 1.07, 1.44); when the AIP was ≥0.10, it showed a significant negative association with unstable carotid plaque (OR: 0.78, 95% CI: 0.70, 0.88). Conclusions: Our findings demonstrated an inverted U-shaped association between the AIP and the risk of unstable carotid plaque, with a threshold of 0.10. The AIP could serve as a potential biomarker for unstable carotid plaque risk assessment.