Role of nutritional status and inflammation in higher survival of African American and Hispanic hemodialysis patients

Abstract

Background: Observational studies indicate greater survival in African American and Hispanic maintenance hemodialysis patients compared with their non-Hispanic white counterparts, although African Americans have shorter life expectancy than whites in the general population. We hypothesized that this apparent survival advantage is due to a more favorable nutritional/inflammatory profile in minority hemodialysis patients.

Study design: We examined the association between race/ethnicity and 5-year survival before and after adjustment for case-mix and surrogates of the malnutrition-inflammation complex syndrome (MICS) using Cox regression with or without matched sampling in a large cohort of adult hemodialysis patients.

Setting & participants: 124,029 adult hemodialysis patients, including 16% Hispanics, 49% non-Hispanic whites, and 35% African Americans.

Predictors: Race/ethnicity before and after adjustment for MICS, including values for body mass index, serum albumin, total iron-binding capacity, ferritin, creatinine, phosphorus, calcium, bicarbonate, white blood cell count, lymphocyte percentage, hemoglobin, and protein intake.

Outcomes: 5-year (July 2001 to June 2006) survival.

Results: In dialysis patients, blacks and Hispanics had lower mortality overall than non-Hispanic whites after traditional case-mix adjustment. However, after additional control for MICS, Hispanics had mortality similar to non-Hispanic whites, and African Americans had even higher mortality. Unadjusted, case-mix-, and MICS-adjusted HRs for African Americans versus whites were 0.68 (95% CI, 0.66-0.69), 0.89 (95% CI, 0.86-0.91), and 1.06 (95% CI, 1.03-1.09) in the unmatched cohort and, 0.95 (95% CI, 0.90-0.99), 0.89 (95% CI, 0.84-0.94), and 1.16 (95% CI, 1.07-1.26) in the matched cohort, and for Hispanics versus whites, 0.66 (95% CI, 0.64-0.69), 0.84 (95% CI, 0.81-0.87), and 0.97 (95% CI, 0.94-1.00) in the unmatched cohort and 0.89 (95% CI, 0.84-0.95), 0.88 (95% CI, 0.83-0.95), and 0.98 (95% CI, 0.91-1.06) in the matched cohort, respectively.

Limitations: Adjustment cannot be made for unmeasured confounders.

Conclusions: Survival advantages of African American and Hispanic hemodialysis patients may be related to differences in nutritional and inflammatory status. Further studies are required to explore these differences.

Copyright © 2011 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Algorithm (flow chart) of the cohort creation.

Figure 2

Mortality hazard ratios (from Cox regression) from the unmatched cohort comparing 43,974 African American to 60,657 non-Hispanic White HD patients over a 5-year observation period (7/2001–6/2006). Cox regression based hazard ratios of death are represented by filled circles for unadjusted model, unfilled circles for case-mix-adjusted model, and filled triangles for case-mix and MICS adjusted models. Error bars represent 95% confidence intervals. Matched cohort was created by 1:1 matching each African American to a non-Hispanic White, matching on gender, age (±5 years), diabetes, entry calendar quarter, and patient residence location (one of the 50 States or the District of Columbia). Case-mix adjusted models include adjustment for age, gender, diabetes mellitus, standardized mortality ratio, race, vintage, primary insurance, marital status, dialysis dose, dialysis catheter, and baseline comorbid states. Malnutrition-inflammation complex syndrome (MICS) model covariate include all case-mix covariates (see above) plus urea kinetics calculated protein catabolic rate (nPNA or nPCR), serum levels of albumin, creatinine, total iron binding capacity (TIBC), calcium, phosphorous, bicarbonate, ferritin; blood white blood cells (WBC) and lymphocyte percentage.

Figure 3

Cox Mortality hazard ratios (from Cox regression) from the unmatched cohort comparing 19,398 Hispanic to 60,657 non-Hispanic White HD patients over a 5-year observation period (7/2001–6/2006). Cox regression based hazard ratios of death are represented by filled circles for unadjusted model, unfilled circles for case-mix-adjusted model, and filled triangles for case-mix and MICS adjusted models. Error bars represent 95% confidence intervals. Matched cohort was created by 1:1 matching each Hispanic patient to a non-Hispanic White, matching on gender, age (±5 years), diabetes, entry calendar quarter, and State of patients’ residence (one of the 50 States or the District of Columbia). Case-mix adjusted models include adjustment for age, gender, diabetes mellitus, standardized mortality ratio, race, vintage, primary insurance, marital status, dialysis dose, dialysis catheter, and baseline comorbid states. Malnutrition-inflammation complex syndrome (MICS) model covariate include all case-mix covariates (see above) plus urea kinetics calculated protein catabolic rate (nPNA or nPCR), serum levels of albumin, creatinine, total iron binding capacity (TIBC), calcium, phosphorous, bicarbonate, ferritin; blood white blood cells (WBC) and lymphocyte percentage.

Figure 4

Mortality hazard ratios (from Cox regression) from the unmatched cohort comparing 43,974 African American to 19,398 non-Hispanic White HD patients over a 5-year observation period (7/2001–6/2006). Cox regression based hazard ratios of death are represented by filled circles for unadjusted model, unfilled circles for case-mix-adjusted model, and filled triangles for case-mix and MICS adjusted models. Error bars represent 95% confidence intervals. Matched cohort was created by 1:1 matching each Hispanic to an African American, matching on gender, age (±5 years), diabetes, entry calendar quarter, and State of patients’ residence (one of the 50 States or the District of Columbia). Case-mix adjusted models include adjustment for age, gender, diabetes mellitus, standardized mortality ratio, race, vintage, primary insurance, marital status, dialysis dose, dialysis catheter, and baseline comorbid states. Malnutrition-inflammation complex syndrome (MICS) model covariate include all case-mix covariates (see above) plus urea kinetics calculated protein catabolic rate (nPNA or nPCR), serum levels of albumin, creatinine, total iron binding capacity (TIBC), calcium, phosphorous, bicarbonate, ferritin; blood white blood cells (WBC) and lymphocyte percentage.

Figure 5

Subgroup survival analyses in the unmatched cohort comparing the mortality hazard ratios for African Americans (Right Panel) or Hispanics (Left panel) to Non-Hispanic Whites in 124,029 long-term HD patients (including 16% Hispanics, 49% non-Hispanic Whites and 35% non-Hispanic African Americans) over a 5-year observation period (7/2001–6/2006). Cox regression based hazard ratios of death are represented by filled circles for unadjusted model, unfilled circles for case-mix-adjusted model, and filled triangles for case-mix and MICS adjusted models. Error bars represent 95% confidence intervals. Case-mix adjusted models include adjustment for age, gender, diabetes mellitus, standardized mortality ratio, race, vintage, primary insurance, marital status, dialysis dose, dialysis catheter, and baseline comorbid states. Malnutrition-inflammation complex syndrome (MICS) model covariate include all case-mix covariates (see above) plus urea kinetics calculated protein catabolic rate (nPNA or nPCR), serum levels of albumin, creatinine, total iron binding capacity (TIBC), calcium, phosphorous, bicarbonate, ferritin; blood white blood cells (WBC) and lymphocyte percentage.