Factors associated with readmission risk in patients with HIV stratified by BMI: a hospital-based retrospective matched cohort study

Background The role of body mass index (BMI) as an effect modifier for readmission risk in people with HIV (PWH) remains underexplored. Objective To compare factors associated with two-year all-cause readmission in PWH, stratified by baseline BMI. Methods A retrospective matched (1:1 by age/sex) cohort study was conducted at a major public infectious diseases hospital in Shenzhen, China, serving a diverse urban population including migrants and low-income individuals. Adults admitted (Jan–Jun 2020) were stratified into underweight (BMI < 18.5 kg/m², n = 80) and normal/overweight (BMI 18.5–<28 kg/m², n = 231) groups. Multivariable logistic regression and ROC analysis were performed within each stratum. Results The readmission rate was higher in the underweight group (61.3% vs. 46.8%, p = 0.023). For underweight PWH, unemployment (adjusted Odds Ratio [aOR] = 8.11, 95% CI 1.82–36.16) and lower nadir CD4 + count (aOR = 0.994 per cell/µL decrease, 95% CI 0.989–0.999) were independent risk factors. For normal/overweight PWH, unemployment (aOR = 2.21, 95% CI 1.12–4.38) and longer time since diagnosis (> 5 vs. 0–1 years, aOR = 4.28, 95% CI 2.02–9.07) were risk factors, while being widowed/divorced was protective (aOR = 0.30, 95% CI 0.10–0.86). Predictive models showed good to excellent accuracy (AUCs: 0.820 and 0.748, respectively). Conclusions Risk factors for readmission differ markedly by baseline BMI, confirming its role as an effect modifier. Interventions should be tailored: integrated nutritional and immunological support for underweight PWH, and chronic disease management with attention to social determinants for others.