Threshold Effect of Glycated Hemoglobin and Linear Association of Body Mass Index with Peripheral Arterial Disease: A Cross‑Sectional Analysis of NHANES Adults

This preregistration archives the pre-specified statistical analysis plan for a cross-sectional analysis using publicly available NHANES 1999–2004 data. The study evaluates linear and nonlinear associations of glycated hemoglobin (HbA1c) and body mass index (BMI) with prevalent peripheral arterial disease (PAD), defined as an ankle–brachial index (ABI) < 0.90, among US adults aged ≥ 40 years. Survey-weighted multivariable logistic regression and restricted cubic spline models will be used, and a sensitivity analysis excluding participants with diagnosed diabetes will test whether the HbA1c threshold association persists. This preregistration is distinct from OSF project 96cru, which addresses prevalence–prognosis effect dissociation with mortality endpoints; the present preregistration covers only the cross-sectional HbA1c–PAD and BMI–PAD analyses. Corresponding author: Shunchi Xu (x.sc001@163.com).