Methodological limitations of the ESRD Core Indicators Project: an ESRD network's experience with implementing an ESRD quality survey. Medical Review Board of the ESRD Network of New England

Protein carbamylation in kidney disease: pathogenesis and clinical implications

Carbamylation describes a nonenzymatic posttranslational protein modification mediated by cyanate, a dissociation product of urea. When kidney function declines and urea accumulates, the burden of carbamylation naturally increases. Free amino acids may protect proteins from carbamylation, and protein carbamylation has been shown to increase in uremic patients with amino acid deficiencies. Carbamylation reactions are capable of altering the structure and functional properties of certain proteins and have been implicated directly in the underlying mechanisms of various disease conditions. A broad range of studies has demonstrated how the irreversible binding of urea-derived cyanate to proteins in the human body causes inappropriate cellular responses leading to adverse outcomes such as accelerated atherosclerosis and inflammation. Given carbamylation's relationship to urea and the evidence that it contributes to disease pathogenesis, measurements of carbamylated proteins may serve as useful quantitative biomarkers of time-averaged urea concentrations while also offering risk assessment in patients with kidney disease. Moreover, the link between carbamylated proteins and disease pathophysiology creates an enticing therapeutic target for reducing the rate of carbamylation. This article reviews the biochemistry of the carbamylation reaction, its role in specific diseases, and the potential diagnostic and therapeutic implications of these findings based on recent advances.

ESRD Networks: past, present, and challenges for the future

Established by Federal law in 1978, the ESRD Networks are regional nonprofit organizations that contract with the Centers for Medicare and Medicaid Services to provide quality oversight services to chronic dialysis facilities. The governing bodies and medical review boards of each network are populated by volunteer professionals and patients. The medical review boards drive the quality agenda for each network, addressing specific local barriers to improvement. The network contract deliverables are defined by the Centers for Medicare and Medicaid Services in a scope of work document (SOW) that is generally revised with each 3-year contracting cycle. The current SOW has not been revised since the implementation of the new Conditions for Coverage for dialysis facilities in 2008 or the implementation of a bundled payment system and quality incentive program for dialysis providers in 2011. The future success of the ESRD Network Program will depend upon adequate funding, data accessibility to drive rapid-cycle quality improvement efforts, and partnerships with other stakeholder groups to address the continuum of care of patients with CKD. The Forum of ESRD Networks has developed a strategic plan that aligns the priorities of the networks with the National Quality Strategy. The integration of these objectives into the next SOW will augment the relevance of the network program to the ESRD stakeholder community as the networks move from a task-oriented approach to a system-improvement approach to quality oversight.

Clinical outcomes and dialysis adequacy in adolescent hemodialysis patients

BACKGROUND

The National Kidney Foundation-Kidney Disease Outcomes Quality Initiative guidelines recommend that adult hemodialysis (HD) patients receive a minimum dialysis dose by single-pooled Kt/V (spKt/V) of 1.2 or greater. There are no data to support a minimum spKt/V dose for children on HD therapy. We aim to determine the association of spKt/V with mortality and hospitalization in adolescents.

METHODS

Clinical characteristics of adolescent HD patients aged 12 to 18 years old included in the 2000/2001 End-Stage Renal Disease Clinical Performance Measures Project were linked to US Renal Data System data from October 1, 1999, to October 15, 2001. Hospitalization risks after adjustment for time on dialysis therapy, access, hemoglobin level, albumin level, and height were determined by means of Poisson regression. spKt/V was analyzed by the adult target (< versus > or = 1.2) and by intervals.

RESULTS

There were 613 patients with 477 patient-years of follow-up, during which there were 14 deaths and 185 hospitalizations covering 1,108 days. After adjustment, patients with an spKt/V less than 1.2 had increased hospitalization risk (1.59; 95% confidence interval, 0.98 to 2.56; P = 0.06) compared with those with an spKt/V of 1.2 or greater. Compared with patients with an spKt/V of 1.2 to 1.4, patients with an spKt/V less than 1.2 had increased adjusted risk for hospitalization (2.46; 95% confidence interval, 1.23 to 4.94; P = 0.01). Increases in spKt/V beyond 1.4 were not associated with improved outcomes.

CONCLUSION

Applying the current adequacy guideline to adolescent HD patients is justified by the increased hospitalization risk of those who fail to attain an spKt/V of 1.2 or greater. However, attaining an spKt/V in excess of 1.4 was not associated with greater benefit.

Changing hemodialysis thresholds for optimal survival

BACKGROUND

The urea reduction ratio (URR), a measure quantitating solute removal during hemodialysis, is the fractional reduction of the blood urea concentration during a single hemodialysis treatment. The URR is the principal measure of hemodialysis dose in the United States. Based on studies of patients dialyzed prior to 1994, a minimum URR value of 65% was recommended to optimize survival. Because of new hemodialysis technologies and evolving demographics of the hemodialysis population, the relationship between the amount of hemodialysis and mortality was examined in contemporary cohorts.

METHODS

This retrospective cohort included> 15,000 patients per year receiving hemodialysis during 1994 through 1997. Each patient's URR was averaged for the three months prior to the beginning of each year. Mortality odds ratios were calculated for patients by URR. To determine the URR value above which no further improvement in mortality was seen ("threshold"), spline functions were tested in logistic regression models, both unadjusted and adjusted for case mix measures. The strength of fit for URR, defined by a range of candidate thresholds from 55 to 75%, was evaluated in increments of 1% for each year using spline functions.

RESULTS

The median URR was 63.2, 65.4, 67.4, and 68.1% for 1994 through 1997, respectively. The median length of hemodialysis treatments increased only six minutes from the beginning to the end of the period of analysis. Using spline functions, the threshold URR values were 61.1, 65.0, 68.0, and 71.0% for 1994 through 1997 in models adjusted for case mix. The ratio of median URR to URR threshold decreased from 1.03 in 1994 to 0.97 in 1997.

CONCLUSIONS

From 1994 to 1997, the median URR and the URR threshold for mortality benefit increased. Although an increased need in the amount of hemodialysis may be a consequence of changes in patients' demographic characteristics, the likely explanation(s) is a change in the dialysis procedure and/or blood sampling favoring higher URR values without changing the amount of dialysis provided. The recommended minimum URR of 65% appears to be too low to confer an optimal mortality benefit in the context of current practices.

Exploring the reverse J-shaped curve between urea reduction ratio and mortality

BACKGROUND

Although accepted worldwide as valid measures of dialysis adequacy, neither the Kt/V (urea clearance determined by kinetic modeling) nor the urea reduction ratio (URR) have unambiguously predicted survival in hemodialysis patients. Because the ratio Kt/V can be high with either high Kt (clearance x time) or low V (urea volume of distribution) and V may be a proxy for skeletal muscle mass and nutritional health, we hypothesized that the increase in the relative risk of death observed among individuals dialyzed in the top 10 to 20% of URR or Kt/V values might reflect a competing risk of malnutrition.

METHODS

A total of 3,009 patients who underwent bioelectrical impedance analysis were stratified into quintiles of URR. Laboratory indicators of nutritional status and two bioimpedance-derived parameters, phase angle and estimated total body water, were compared across quintiles. The relationship between dialysis dose and mortality was explored, with a focus on how V influenced the structure of the dose-mortality relationship.

RESULTS

There were statistically significant differences in all nutritional parameters across quintiles of URR or Kt/V, indicating that patients in the fifth quintile (mean URR, 74.4 +/- 3.1%) were more severely malnourished on average than patients in all or some of the other quintiles. The relationship between URR and mortality was decidedly curvilinear, resembling a reverse J shape that was confirmed by statistical analysis. An adjustment for the influence of V on URR or Kt/V was performed by evaluating the Kt-mortality relationship. There was no evidence of an increase in the relative risk of death among patients treated with high Kt. Higher Kt was associated with a better nutritional status.

CONCLUSION

We conclude that the increase in mortality observed among those patients whose URR or Kt/V are among the top 10 to 20% of patients reflects a deleterious effect of malnutrition (manifest by a reduced V) that overcomes whatever benefit might be derived from an associated increase in urea clearance. Identification of patients who achieve extremely high URR (>75%) or single-pooled Kt/V (>1.6) values using standard dialysis prescriptions should prompt a careful assessment of nutritional status. Confounding by protein-calorie malnutrition may limit the utility of URR or Kt/V as a population-based measure of dialysis dose.

Relationship between urea reduction ratio, demographic characteristics, and body weight for patients in the 1996 National ESRD Core Indicators Project

The 1996 Health Care Financing Administration's (HCFA) Core Indicators Project for in-center, hemodialysis patients collects information on the quality of care delivered in four clinical areas that were anticipated to predict patient outcomes. Included among these clinical performance measurements is the delivered dose of hemodialysis, measured by the fractional reduction of urea achieved during a single hemodialysis session (urea reduction ratio [URR]). A random sample (N = 7,310) of adult (aged > or =18 years), in-center hemodialysis patients was selected, and a one-page data collection form for each patient was sent to the dialysis facility in which care was provided during the last quarter of 1995. The dialysis facilities provided information for 6,861 (94%) patients, and at least one paired predialysis and postdialysis blood urea nitrogen (BUN) concentration was reported for 6,655 (97%) of these patients. The URR of this cohort was 65.5% +/- 8.0% (mean +/- SD), and 41% of patients had a URR less than 65%. The mean dialysis session length was 203 minutes, and more than half of the patients received dialysis with a dialyzer membrane with a KUf less than 10 mL/mm Hg/h. The patients with a URR less than 65% had a mean body weight approximately 10 kg greater than patients with a URR of 65% or greater. This relationship was present for all demographic characteristics studied, including age, gender, race, and primary cause of end-stage renal disease (ESRD). Patients receiving dialysis for less than 6 months were more likely to have a URR less than 65% than patients on dialysis for longer periods. By multivariate analysis, variables significantly associated with a delivered URR less than 65% were body weight in the heaviest quartile (odds ratio [OR] = 6.1), male gender (OR = 2.6), on dialysis therapy less than 6 months (OR = 2.5), youngest quartile of age (<49 years) (OR = 2.0), lowest quartile of serum albumin values less than 3.6 g/dL (bromcresol green method) or less than 3.3 g/dL (bromcresol purple method) (OR = 1.6), black (OR = 1.5), dialyzed with a dialyzer KUf less than 20 mL/mm Hg/h (OR = 1.8), lowest quartile hematocrit (<29.7%) (OR = 1.2), and shorter dialysis session length (OR = 1.02/min). In conclusion, both patient-specific demographic variables and treatment-specific parameters are significantly associated with ESRD patients receiving a URR less than 65%. Furthermore, these data suggest statistically significant linkages between the delivered dose of hemodialysis and other independent outcome predictors such as serum albumin concentration. Prospective study is required to determine whether intervention strategies to improve the delivered dose of hemodialysis will affect this outcome predictor or whether serum albumin and dialysis dose share a common cause not amenable to increasing the URR.

Barriers to adequate protein nutrition among hemodialysis patients

OBJECTIVE

Determine the relative importance of potential medical, behavioral, and socioeconomic barriers to adequate protein nutrition among hemodialysis patients.

DESIGN

Cross-sectional study.

SETTING

All 22 chronic hemodialysis units in northeast Ohio.

PATIENTS

298 randomly selected chronic hemodialysis patients.

INTERVENTION

We interviewed and abstracted the chart of each patient to assess protein nutritional status (albumin and protein catabolic rate), potential medical barriers (poor appetite, inadequate dialysis, bioincompatible dialysis membrane, difficulty chewing, and comorbid conditions), potential behavioral barriers (knowledge of protein containing foods and dietary noncompliance), and potential socioeconomic barriers (expense of protein containing foods and needing help shopping and cooking).

MAIN OUTCOME MEASURE

We used logistic regression to examine the relationship between protein nutritional status and potential barriers.

RESULTS

Albumin levels of <35 g/L were independently associated with Kt/V of <1.2 (odds ratio, 2.4), having more than three comorbid conditions (odds ratio, 4.0), inability to name any protein-containing foods (odds ratio, 2. 3), and needing help shopping and cooking (odds ratio, 2.6). Normalized protein catabolic rate of <1.0 g/kg/d was independently associated with poor appetite (odds ratio, 3.3), Kt/V of <1.2 (odds ratio, 3.1), and dietary compliance as indicated by low interdialytic fluid gain (odds ratio, 2.2).

CONCLUSION

Three medical factors (poor appetite, inadequate dialysis, and comorbid conditions), two behavioral factors (lack of knowledge of protein containing foods and low interdialytic fluid gain), and one socioeconomic factor (needing help shopping and cooking) are independently associated with inadequate protein nutrition among hemodialysis patients. Further work is needed to develop interventions to overcome these barriers and to determine the effect of such interventions on protein nutrition and patient mortality and morbidity.