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

Reverse epidemiology of cardiovascular risk factors in maintenance dialysis patients

Conventional risk factors of cardiovascular disease and mortality in the general population such as body mass, serum cholesterol, and blood pressure are also found to relate to outcome in maintenance dialysis patients, but often in an opposite direction. Obesity, hypercholesterolemia, and hypertension appear to be protective features that are associated with a greater survival among dialysis patients. A similar protective role has been described for high serum creatinine and possibly homocysteine levels in end-stage renal disease (ESRD) patients. These findings are in contrast to the well-known association between over-nutrition and poor outcome in the general population. The association between under-nutrition and adverse cardiovascular outcome in dialysis patients, which stands in contrast to that seen in non-ESRD individuals, has been referred to as "reverse epidemiology." Publication bias may have handicapped or delayed additional reports with such paradoxical findings in ESRD patients. The etiology of this inverse association between conventional risk factors and clinical outcome in dialysis patients is not clear. Several possible causes are hypothesized. First, survival bias may play a role since only a small number of patients with chronic kidney disease (CKD) survive long enough to reach ESRD. Hence, the dialysis patients are probably a distinctively selected population out of CKD patients and may not represent the risk factor constellations of their CKD predecessors. Second, the time discrepancy between competitive risk factors may play a role. For example, the survival disadvantages of under-nutrition, which is frequently present in dialysis patients, may have a major impact on mortality in a shorter period of time, and this overwhelms the long-term negative effects of over-nutrition on survival. Third, the presence of the "malnutrition-inflammation complex syndrome" (MICS) in dialysis patients may also explain the existence of reverse epidemiology in dialysis patients. Both protein-energy malnutrition and inflammation or the combination of the two are much more common in dialysis patients than in the general population and many elements of MICS, such as low weight-for-height, hypocholesterolemia, or hypocreatininemia, are known risk factors of poor outcome in dialysis patients. The existence of reverse epidemiology may have a bearing on the management of dialysis patients. It is possible that new standards or goals for such traditional risk factors as body mass, serum cholesterol, and blood pressure should be considered for these individuals.

Impact of renal transplantation on survival in end-stage renal disease patients with elevated body mass index

BACKGROUND

Cadaveric renal transplantation is associated with a survival advantage compared with dialysis patients remaining on the renal transplantation waiting list, but this advantage has not been confirmed in obese end-stage renal disease (ESRD) patients.

METHODS

Using data from the USRDS, we studied 7521 patients who presented with ESRD from 1 April 1995 to 29 June 1999 and later enrolled on the renal transplantation waiting list with body mass indices (BMI) >or=30 kg/m(2) at the time of presentation to ESRD, and followed until 6 November 2000. Recipients of preemptive renal transplantation or organs other than kidneys were excluded. Cox non-proportional hazards regression models were used to calculate adjusted, time-dependent hazard ratios (HR) for time to death in a given patient during the study period, controlling for renal transplantation, demographics and comorbidities (Form 2728).

RESULTS

The incidence of mortality was 3.3 episodes per 100 patient-years (PY) in cadaveric renal transplantation and 1.9/100 PY in living donor renal transplantation compared with 6.6 episodes/100 PY in all patients on the transplant waiting list. In comparison to maintenance dialysis, both recipients of solitary cadaveric kidneys (HR 0.39, 95% CI 0.33 to 0.47), and recipients of living donor kidneys (HR 0.23, 95% CI 0.16 to 0.34) had statistically significant improved survival. A benefit of cadaveric renal transplantation did not apply to patients with BMI >or=41 kg/m(2) (HR 0.47, 95% CI, 0.17 to 1.25, P = 0.13).

CONCLUSIONS

Obese patients on the renal transplant waiting list had a significantly lower risk of mortality after renal transplantation compared with those remaining on dialysis.

Prescribing hemodialysis: the role of gender

Mortality rates remain high in the United States for people who depend on artificial kidney replacement for their existence, and the mortality rates are similar in men and women. However, women differ from men in many respects; some of these ways may have an impact on the response to dialysis through mechanisms that need to be further explored. Observational studies have shown that women respond more readily to a higher dose of dialysis, and recent data from the HEMO clinical trial suggest that women respond to an increase in clearance of low-molecular-weight uremic toxins, whereas men do not. If the findings of these studies prove to be accurate, then we may conclude not only that women require a higher dose of dialysis as currently measured, but we might also expect women to require dialysis sooner during the course of a progressive decline in renal function. The reason for this gender-dependent difference in susceptibility escapes definition at the present time, but size is an obvious confound that can be explored by using current data and in future studies. More detailed analyses of the HEMO data are forthcoming and may shed further light on this question.