Body mass index and mortality in 'healthier' as compared with 'sicker' haemodialysis patients: results from the Dialysis Outcomes and Practice Patterns Study (DOPPS)

Background. Haemodialysis (HD) patients with lower body mass index (BMI) ha ve a higher relative mortality risk (RR), irrespective of race. However, on ly Asian Americans treated with HD have been found to have an elevated RR w ith higher BMI. Asian Americans on HD are 'healthier' than other race group s (i.e. have better overall survival). We hypothesized that an increased mo rtality risk might be associated with high BMI in a variety of other 'healt hier' subgroups of HD patients. Methods. The prospective Dialysis Outcomes and Practice Patterns Study (DOP PS) provided baseline demographic. comorbidity and BMI data on 9714 HD pati ents in the US and Europe (France. Germany, Italy, Spain, and the UK) from 1996-2000. Using multivariate survival analyses, we evaluated BMI-mortality relationships in HD subpopulations defined by continent, race (black and w hite), gender, tertiles of severity of illness (based on a score derived fr om comorbid conditions and serum albumin concentration), age (<45, 45-64, < greater than or equal to>65), smoking, and diabetic status. Results. Relative mortality risk decreased with increasing BMI. This was st atistically significant (P<0.007) except for the smallest subgroup of patie nts who were <45 years old and were also in the healthiest tertile of comor bidity. All else equal, BMI <20 was consistently associated with the highes t relative mortality risk. Overall a lower relative mortality risk (RR) as compared with BMI 23-24.9. was found for overweight (BMI 25-29.9; RR 0.84. P=0.008), for mild obesity (BMI 30-34.9: RR 0.73 P=0.0003). and for moderat e obesity (BMI 35-39.9; RR 0.76, P = 0.02). Conclusion. In a wide variety of HD patient subgroups, differing with respe ct to their baseline health status. increasing body size correlates with a decreased mortality risk. This contrasts with the association between BMI a nd mortality in the general population, and deserves further study.