Special Announcement
Testing for Chronic Kidney Disease: A Position Statement From the National Kidney Foundation

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Chronic kidney disease (CKD) is common in the United States. The estimated prevalence of CKD in US adults was 11.7% ± 0.8% in 2000, based on the National Health and Nutrition Examination Survey (NHANES). Global estimates for CKD prevalence are less certain, but recent studies in Europe, Australia, and China suggest a high prevalence. The most common risk factors for CKD include diabetes, hypertension, cardiovascular disease, a family history of CKD, and age greater than 60 years. Major outcomes of CKD include progression to kidney failure, development of complications of impaired kidney function, and increased risk for cardiovascular disease. CKD is usually silent until its late stages, thus many patients with CKD are detected only shortly before the onset of symptomatic kidney failure, when there are few opportunities to prevent adverse outcomes. Earlier detection allows for more time for evaluation and treatment but requires explicit testing strategies for asymptomatic individuals at increased risk. In the majority of patients, CKD can be detected with 2 simple tests: a urine test for the detection of proteinuria and a blood test to estimate the glomerular filtration rate (GFR). These 2 tests facilitate detection of CKD by all physicians by allowing for identification of CKD without first requiring determination of its cause. Understanding the strengths and limitations of CKD testing is critical for appropriate implementation of these recommendations. Application of CKD testing in national and international screening and surveillance programs could improve public health related to CKD.

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CKD Prevalence, Risk Factors, and Outcomes

CKD is common in the United States. In 2000, approximately 398,000 people (0.2%) were treated by dialysis or transplantation for chronic kidney failure, the end stage of CKD.7 By 2030, this number is expected to rise to more than 2 million people.8 The estimated prevalence of earlier stages of CKD in US adults was 20 million (11.7%) in 2000, based on the National Health and Nutrition Examination Survey (NHANES)9; there are not yet projections for future prevalence of CKD. Worldwide prevalence

CKD Definition and Testing

CKD is defined by the presence of kidney damage or glomerular filtration rate (GFR) less than 60 mL/min/1.73 m2 (1.0 mL/s/1.73 m2) for 3 or more months, irrespective of cause (Table 4).5, 6 Markers of kidney damage include abnormalities in the serum or urine, or on imaging studies, and reflect the underlying pathology. Proteinuria is the earliest marker of kidney damage in diabetes, hypertension, and glomerular diseases; thus it is the most common marker of kidney damage in adults.5 GFR is

Proteinuria

Proteinuria refers to increased excretion of any urinary protein, including albumin and other serum proteins, and proteins synthesized by the tubule (Tamm-Horsfall protein) or in the lower urinary tract. Albuminuria refers to increased excretion of albumin only. In this article, we refer to testing for proteinuria as tests for detection of proteinuria, including tests for albumin only. We refer to testing for albuminuria as tests for detection of albumin only.

Healthy individuals usually excrete

Interpretation of CKD Tests

Persistent proteinuria or reduction in GFR to below 60 mL/min/1.73 m2 (1.0 mL/s/1.73 m2) is defined as CKD. The lesser accuracy of current estimating equations at higher levels of GFR may make it difficult to interpret GFR estimates near 60 mL/min/1.73m2 (1.0 mL/s/1.73 m2) in some people. In this range, interpretation of GFR estimates depends on the results of tests for markers of kidney damage and the clinical context (Table 9). Patients with proteinuria have CKD even if GFR estimates are 60

Limitations

There are 3 main limitations to the current testing recommendations. First, there is a variable rate of false-positive tests for both urine protein and estimated GFR, depending upon the population screened. Repeated measurements, with confirmation of persistence of abnormal results over 3 months, will diminish the false-positive rate of urine protein testing. Attention to the clinical setting will facilitate proper interpretation of both urine protein and estimated GFR. Second, there is

Application to Public Health Programs

The strategy of screening for CKD by testing both for markers of kidney damage and for the level of kidney function has now been applied in NHANES and in the National Kidney Foundation’s Kidney Early Evaluation Program (KEEP). NHANES is an ongoing survey of a stratified random sample of the noninstitutionalized US population. Data from more than 25,000 people since 1988 has been critical to demonstrate prevalence of CKD, associations with comorbid conditions, and trends over time.9, 41 In the

Acknowledgements

This paper has been approved as the official position of the National Kidney Foundation by the Scientific Advisory Board and Board of Directors.

Support: Dr Vassalotti is the Chief Medical Officer of the National Kidney Foundation. Dr Stevens is Program Director, Implementation, at the National Kidney Foundation Center for Guideline Development and Implementation at Tufts-New England Medical Center; Dr Levey is Director of that center and Editor-in-Chief of AJKD.

Financial Disclosure: Dr Levey

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