Obesity is a risk factor for peritonitis in the Australian and New Zealand peritoneal dialysis patient populations.

Objective: The aim of the present investigation was to examine the association between body mass index (BMI) and peritonitis rates among incident peritoneal dialysis (PD) patients in a large cohort with long-term follow-up.

Design: Retrospective observational cohort study of the Australian and New Zealand PD patient population.

Setting: Australia and New Zealand Dialysis and Transplant (ANZDATA) Registry.

Participants: The study included all incident adult patients (n = 10 709) who received PD in Australia and New Zealand in the 12-year period between 1 April 1991 and 31 March 2003. Patients were classified as obese (BMI > or = 30 kg/m2), overweight (BMI 25.0 - 29.9 kg/m2), normal weight (20 - 24.9 kg/m2), or underweight (< 20 kg/m2).

Main Measurements: Time to first peritonitis and episodes of peritonitis per patient-year were recorded over the 12-year period.

Results: Higher BMI was associated with a shorter time to first peritonitis episode, independent of other risk factors [hazard ratio 1.08 for each 5-kg/m2 increase in BMI, 95% confidence interval (CI) 1.04 - 1.12, p < 0.001]. When peritonitis outcomes were analyzed as episodes of peritonitis per patient-year, these rates were significantly higher among patients with higher BMI: underweight 0.69 episodes/year (95% CI 0.66 - 0.73), normal weight 0.79 (95% CI 0.77 - 0.81), overweight 0.88 (95% CI 0.85 - 0.90), obese 1.06 (95% CI 1.02 - 1.09). Coronary artery disease and chronic lung disease were associated with both shorter time to first peritonitis and higher peritonitis rates, independently of these other factors. There was also a "vintage effect," with lower peritonitis rates seen among people who commenced dialysis in more recent years.

Conclusions: Higher BMI at the commencement of renal replacement therapy is a significant risk factor for peritonitis. The mechanisms for this remain undefined.