New body mass index for predicting prognosis in patients with antineutrophil cytoplasmic antibody‐associated vasculitis

OBJECTIVES: Body mass index (BMI) is a known indicator of all‐cause mortality. However, conventional BMI does not reflect the three‐dimensional human body. To overcome this limitation, a new BMI has been proposed that provides a closer approximation of real human body shape. This study investigated the associations between the new BMI and poor outcomes in patients with antineutrophil cytoplasmic antibody‐associated vasculitis (AAV). METHOD: We retrospectively reviewed the medical records of 242 patients with AAV in a single tertiary medical center. Based on the new BMI, the patients were categorized into four groups: underweight (<18.5 kg/m(2.5)), healthy weight (18.5 to <25.0 kg/m(2.5)), overweight (25.0 to <30.0 kg/m(2.5)), and obese (≥30.0 kg/m(2.5)). The association among the new BMI and death, relapse, end‐stage renal disease (ESRD) development, cerebrovascular accident, and cardiovascular disease was analyzed. RESULTS: The underweight group, according to the new BMI, had higher hazard ratios (HRs) for all‐cause mortality (HR: 3.180, 95% confidence interval [CI]: 1.134–8.922, p = 0.028), relapse (HR: 2.141, 95% CI: 1.019–4.368, p = 0.036), and ESRD development (HR: 2.729, 95% CI: 1.190–6.259, p = 0.018) than the healthy weight group. However, according to the conventional BMI, there were no differences in the risks for all poor outcomes between the underweight and healthy weight groups. Multivariate logistic regression analysis demonstrated that being underweight, according to the new BMI, was an independent risk factor for all‐cause mortality (HR: 5.285; 95% CI: 1.468–19.018; p = 0.011). CONCLUSION: Being underweight, according to the new BMI, is associated with poor outcomes in patients with AAV.