Overweight/obesity revisited as a predictive risk factor in primary IgA nephropathy

Background. The absolute renal risk (ARR) of dialysis/death in IgA nephropathy (IgAN) was based on three major, independent equipotent risk factors: hypertension, proteinuria >= 1 g/day and severe pathological score at diagnosis. We studied, in our prospective regional cohort of IgAN, the impact of body mass index (BMI) on the ultimate outcome in light of this ARR concept. Methods. We had information on 331 IgAN patients (233 men). At diagnosis, the BMI was normal (<25 kg/m(2)) in 195 and elevated (>= 25) in 136 (44.1%) with 102 overweight (25-29.9) and 34 obese (>= 35) defining two groups, normal BMI and elevated BMI, subsequently compared. Results. At diagnosis, in the overweight/obese group, hypertension and proteinuria >= 1 g/day were more frequent (respectively, P < 0.0001 and P = 0.0006) and the mean global optical score was increased (P = 0.002). This resulted in a worse ARR scoring distribution (P < 0.0001). In addition, these patients with an elevated BMI were similar to 10 years older (P < 0.0001), including more obese women and with an eGFR already lower (P = 0.0003). At last follow-up, in the overweight/obese group, progression remained worse with greater prevalence of CKD-3+ (43.4 versus 21.0%; P < 0.0001) and dialysis/death events (21.3 versus 13.9%). Kaplan-Meier survival and Cox regression analyses demonstrated that ARR remained a powerful independent risk factor for prediction of events, but not BMI. Conclusions. IgAN patients with an elevated BMI at diagnosis had a significantly worse presentation and worse final outcome. Overweight/obesity increased hypertension frequency, proteinuria level and some renal lesions all of which translate into a worse ARR for prediction of CKD-3+ or dialysis alone or dialysis/death, with no apparent direct effect of BMI per se.