Screening for chronic kidney disease complications in US adults: racial implications of a single GFR threshold

Retaining Race in Chronic Kidney Disease Diagnosis and Treatment

The best overall measure of kidney function is glomerular filtration rate (GFR) as commonly estimated from serum creatinine concentrations (eGFRcr) using formulas that correct for the higher average creatinine concentrations in Blacks. After two decades of use, these formulas have come under scrutiny for estimating GFR differently in Blacks and non-Blacks. Discussions of whether to include race (Black vs. non-Black) in the calculation of eGFRcr fail to acknowledge that the original race-based eGFRcr provided the same CKD treatment recommendations for Blacks and non-Blacks based on directly (exogenously) measured GFR. Nevertheless, the National Kidney Foundation and the American Society of Nephrology Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease removed race in CKD treatment guidelines and pushed for the immediate adoption of a race-free eGFRcr formula by physicians and clinical laboratories. This formula is projected to negate CKD in 5.51 million White and other non-Black adults and reclassify CKD to less severe stages in another 4.59 million non-Blacks, in order to expand treatment eligibility to 434,000 Blacks not previously diagnosed and to 584,000 Blacks previously diagnosed with less severe CKD. This review examines: 1) the validity of the arguments for removing the original race correction, and 2) the performance of the proposed replacement formula. Excluding race in the derivation of eGFRcr changed the statistical bias from +3.7 to -3.6 ml/min/1.73m2 in Blacks and from +0.5 to +3.9 in non-Blacks, i.e., promoting CKD diagnosis in Blacks at the cost of restricting diagnosis in non-Blacks. By doing so, the revised eGFRcr greatly exaggerates the purported racial disparity in CKD burden. Claims that the revised formulas identify heretofore undiagnosed CKD in Blacks are not supported when studies that used kidney failure replacement therapy and mortality are interpreted as proxies for baseline CKD. Alternatively, a race-stratified eGFRcr (i.e., separate equations for Blacks and non-Blacks) would provide the least biased eGFRcr for both Blacks and non-Blacks and the best medical treatment for all patients.

Limited Evidence for Use of a Black Race Modifier in eGFR Calculations: A Systematic Review

Background

Commonly used estimated glomerular filtration rate (eGFR) equations include a Black race modifier (BRM) that was incorporated during equation derivation. Race is a social construct, and a poorly characterized variable that is applied inconsistently in clinical settings. The BRM results in higher eGFR for any creatinine concentration, implying fundamental differences in creatinine production or excretion in Black individuals compared to other populations. Equations without inclusion of the BRM have the potential to detect kidney disease earlier in patients at the greatest risk of chronic kidney disease (CKD), but also has the potential to over-diagnose CKD or impact downstream clinical interventions. The purpose of this study was to use an evidence- based approach to systematically evaluate the literature relevant to the performance of the eGFR equations with and without the BRM and to examine the clinical impact of the use or removal.

Content

PubMed and Embase databases were searched for studies comparing measured GFR to eGFR in racially diverse adult populations using the Modification of Diet in Renal Disease or the 2009-Chronic Kidney Disease Epidemiology Collaboration-creatinine equations based on standardized creatinine measurements. Additionally, we searched for studies comparing clinical use of eGFR calculated with and without the BRM. 8,632 unique publications were identified; an additional 3 studies were added post-hoc. In total, 96 studies were subjected to further analysis and 44 studies were used to make a final assessment.

Summary

There is limited published evidence to support the use of a BRM in eGFR equations.

Using race in the estimation of glomerular filtration rates: time for a reversal?

PURPOSE OF REVIEW

Bedside estimates of renal function are essential for clinical practice in the modern era and have largely relied on serum creatinine concentrations despite the known drawbacks associated with this choice of biomarker, including the fact that creatinine clearance overestimates the glomerular filtration rate.

RECENT FINDINGS

Initial estimates relied primarily on equations that incorporated factors known to influence creatinine concentrations such as age, sex and anthropometric measures. More recent estimates of glomerular filtration rate have replaced the anthropometric measures with the social construct of race, suggesting that glomerular filtration rates for black individuals are higher at the same concentration of creatinine. This approach has led to large variations in the estimated differences in glomerular filtration rate between black and nonblack individuals in the United States that have not been reproducible, resulting in a plethora of population-specific formulae across the country.

SUMMARY

The introduction of race in estimated glomerular filtration rate equations may have potential unintended negative consequences for the very population with the greatest burden of kidney disease. These potential disadvantages underscore the need to perhaps return to the replacement of race with more objective anthropometric measures without the loss of precision.

Argyria following the use of silver-coated megaprostheses: no association between the development of local argyria and elevated silver levels

The aims of this study were to evaluate the incidence of local argyria in patients with silver-coated megaprostheses and to identify a possible association between argyria and elevated levels of silver both locally and in the blood. Between 2004 and 2011, 32 megaprostheses with silver coatings were implanted in 20 female and 12 male patients following revision arthroplasty for infection or resection of a malignant tumour, and the levels of silver locally in drains and seromas and in the blood were determined. The mean age of the patients was 46 years (10 to 81); one patient died in the immediate post-operative period and was excluded. Seven patients (23%) developed local argyria after a median of 25.7 months (interquartile range 2 to 44.5). Patients with and without local argyria had comparable levels of silver in the blood and aspiration fluids. The length of the implant did not influence the development of local argyria. Patients with clinical evidence of local argyria had no neurological symptoms and no evidence of renal or hepatic failure. Thus, we conclude that the short-term surveillance of blood silver levels in these patients is not required.

[Ethnicity and vitamin D]

Cohort studies, mainly US, show that vitamin D deficiency is more common in African-American population. Social and environmental factors play a role but the difference in skin color is essential. Despite low 25-hydroxyvitamin D concentrations, a lower risk of fragility or fracture exists in these populations. Vitamin D deficiency is a contributing factor in many chronic diseases. There is a relationship between vitamin D deficiencies, progression of chronic kidney disease and increased relative risk of mortality. If the ethnicity of patients is now taken into account to estimate renal function, probably specific recommendations for vitamin D deficiency are needed.

Re-evaluating the predictive roles of metabolic complications and clinical outcome according to eGFR levels--a four-years prospective cohort study in Taiwan

Background

Metabolic complications are associated with clinical outcomes in patients with chronic kidney disease (CKD). These outcomes differ among patients according to the different stages of disease. The prevalence and association of type and number of metabolic complications with renal progression and death in patients having different eGFR levels has high clinical value, but this fact has been rarely evaluated in prospective studies.

Methods

We prospectively followed a cohort of 1157 CKD patients from 2006 to death or until 2010, and evaluated the prevalence of CKD-related complications and their association with renal progression (defined as a decline in eGFR by > 50% from baseline, or end-stage renal disease requiring dialysis) and death in patients with eGFRs above and below 45 mL/min/1.73 m² using Cox-proportional hazard models.

Results

The estimated rate (per 100 patient-years) of renal progression and death were 11.9 and 4.9, respectively. The eGFR thresholds determined by ROC analysis with a sensitivity of 90% for any metabolic complication were 60.8 mL/min/1.73 m² and 74.3 mL/min/1.73 m² using the MDRD and CKD Epidemiology Collaboration equations, respectively. CKD-related complications associated with renal progression in patients having eGFR < 45 mL/min/1.73 m² were hyperphosphatemia, anemia, microinflammation and hypoalbuminemia. Those CKD-related complications associated with death were hypoalbuminemia and hyperuricemia. Hypoalbuminemia predicted renal progression, and, hypoalbuminemia and microinflammation predicted death in patients with eGFR ≥ 45 mL/min/1.73 m². The number of complications (≥ 3) independently predicted both endpoints in patients with eGFR < 45 mL/min/1.73 m².

Conclusions

Hypoalbuminemia was a unique and strong predictor of renal progression and all-cause mortality in CKD patients, independent of their demographic characteristics, traditional risk factors, renal function severity, the presence of cardiovascular disease and other metabolic abnormalities. Most other metabolic complications and the number of complications (≥3) were associated with the clinical outcomes of patients with eGFR < 45 mL/min/1.73 m² rather than in those with higher eGFRs. The findings from the present study offer a novel insight into the association between metabolic complications and patient outcomes and may help to refine risk stratification according to disease stage.

Elevated serum uric acid predicts chronic kidney disease

INTRODUCTION

The question of whether elevated serum uric acid is an independent risk factor for chronic kidney disease in a longitudinal manner was assessed in Japanese subjects undergoing a health checkup.

METHODS

A total of 14,399 participants (8,161 men and 6,238 women) without medication for hyperuremia in both 2000 and 2005 were included. After exclusion of participants taking treatments influencing serum uric acid and having chronic kidney disease defined as estimated glomerular filtration rate <60 mL/min/1.73 m(2), in 2000, multiple logistic regression analyses were performed for 6,887 men (48.4 ± 9.9 years) and 5,340 women (49.9 ± 9.0 years) to identify independent factors for newly diagnosed chronic kidney disease in 2005. Adjustment was made for age, body mass index, elevated blood pressure or hypertension, hypertriglyceridemia, impaired fasting glucose, either urinary protein or occult blood, alcohol drinking and smoking.

RESULTS

The prevalence of chronic kidney disease and the values of body mass index, systolic and diastolic blood pressure and triglyceride were significantly higher in the participants with elevated serum uric acid quartiles. Chronic kidney disease was newly diagnosed in 4.1% of men and 3.7% of women, within the 5-year period. In multivariate models, the higher quartiles of serum uric acid were associated with increased risk of chronic kidney disease in both sexes. The odds ratio and 95% confidence interval for 1 increment of serum uric acid were 1.42 and 1.28 to 1.58 in men and 1.32 and 1.12 to 1.56 in women, respectively.

CONCLUSIONS

Elevated serum uric acid predicts chronic kidney disease in subjects undergoing a health checkup.