Association of body mass index with decline in residual kidney function after initiation of dialysis.

BACKGROUND: Obesity is a risk factor for loss of kidney function in the general population, but it is unknown whether it proceeds to affect residual kidney function when patients require dialysis. Our aim was to study the effects of body mass index (BMI) on decline in kidney function and risk to develop anuria after initiation of dialysis therapy.

STUDY DESIGN: Prospective cohort study.

SETTING & PARTICIPANTS: 1,271 incident dialysis patients from 38 centers in The Netherlands participating in the Netherlands Cooperative Study on the Adequacy of Dialysis (NECOSAD) between 1997 and 2006.

PREDICTOR: BMI assessed at 3 months after the initiation of dialysis therapy (baseline) and categorized into 4 groups: less than 20, 20 or greater to 25, 25 or greater to 30, and 30 or greater kg/m(2).

OUTCOMES & MEASUREMENTS: The decrease in measured glomerular filtration rate (mGFR) was determined by means of linear mixed models and adjusted for age, sex, primary kidney disease, dialysis modality, smoking, cardiovascular disease, and normalized protein nitrogen appearance and additionally for proteinuria, blood pressure, and baseline mGFR. Cox regression analysis was used to calculate hazard ratios for the development of anuria.

RESULTS: Patients had a mean age of 59 +/- 15 years, BMI of 24.8 +/- 4.1 kg/m(2), and mGFR of 4.7 +/- 3.3 mL/min. During 18 months of follow-up, the decrease in mGFR in patients with normal weight was 1.2 mL/min/y (95% confidence interval [CI], 0.7 to 1.6). Compared with those values, adjusted losses of mGFR were 0.4 mL/min/y (95% CI, 0.02 to 0.8) greater for overweight and 1.2 mL/min/y (95% CI, 0.5 to 1.8) greater for obese patients. In contrast, the decrease in underweight patients was 0.6 mL/min/y (-0.1 to 1.3) less. Anuria occurred in 297 patients; the risk was similar among BMI groups after adjustment for confounders and baseline diuresis.

LIMITATIONS: Patients with missing BMI or mGFR values at baseline were excluded.

CONCLUSION: Obesity is a strong risk factor for the decline in kidney function after initiation of dialysis therapy. Whether obese dialysis patients might benefit from a healthy weight reduction needs to be studied further.