Simple screening questionnaire for kidney disease outperforms current clinical practice guidelines

Mar 1 2008

The general public is not sufficiently aware that chronic kidney disease (CKD) is a serious and progressive medical condition.

It remains under-diagnosed and under-treated. Understandably so, since in its early stages CKD is often asymptomatic, making individuals with the disease and their health-care providers unaware of its "silent" yet threatening presence. However, if CKD is detected and treated early, its widespread consequences -- which include kidney failure, cardiovascular disease (CVD) and even death -- may be prevented or delayed.

In a community-based study and national survey, a team of public health and medical researchers from Weill Cornell Medical College and the University of North Carolina (UNC) at Chapel Hill show that a simple screening questionnaire, SCreening for Occult REnal Disease (SCORED), is better able to identify patients at risk for CKD than the current National Kidney Foundation (NKF) clinical practice guidelines, the Kidney Early Evaluation Program (KEEP). The study has just been published in the Archives of Internal Medicine.

SCORED demonstrates greater accuracy and greater predictive power in identifying individuals at high-risk for CKD than KEEP. In addition, SCORED defines 25 percent fewer screeners as high risk, resulting in fewer unnecessary follow-up tests.

SCORED demonstrates 88 to 95 percent sensitivity (how well the test correctly identifies people who have the disease) and a specificity of 55 to 65 percent (how well the test correctly identifies people who do not have the disease). In comparison, KEEP demonstrates a sensitivity of 86 to 92 percent and a specificity of 24 to 35 percent. Predictive values (the chance that a positive or negative test result will be correct) and the ability to distinguish CKD and non-CKD were also shown to be significantly improved using SCORED.

"Recent national health statistics indicate that about 13 percent of the U.S. population has CKD, while awareness of kidney disease among the general public remains very low," states Dr. Heejung Bang, assistant professor in the Division of Biostatistics and Epidemiology in the Department of Public Health at Weill Cornell Medical College and lead author of the study. "This information underscores the need to be more vigilant in detecting those at risk of CKD in the general population," she says.

SCORED remains the first and only scoring instrument rigorously developed by statistical modeling for general population screening, as reported one year ago -- in the Feb. 26, 2007, Archives of Internal Medicine. It employs a user-friendly questionnaire and a simple scoring system based on seven risk factors for CKD -- age, sex, hypertension, diabetes, cardiovascular disease (CVD), anemia and proteinuria (the presence of excessive protein in the urine). All risk factors for CKD are supported by scientific theory and have been validated by national surveys and community health studies.

"If your total score from the SCORED test is 4 or higher, it doesn't mean you have CKD, but we strongly recommend further blood testing for creatinine (a marker for impaired kidney function) and/or urine exam by a physician. Similarly, having a low score does not guarantee you are free of this disease, but it means you are likely at low risk," says Dr. Bang. (The SCORED questionnaire is available below.)

In contrast, KEEP defines high-risk individuals as those who are 18 years or older with at least one of the following: diabetes; high blood pressure; or a family history of diabetes, high blood pressure or kidney disease.

"The SCORED model seems to improve diagnostic performance because of the use of additional variables, different weights for age groups, and questions about underlying CVD. Indeed, most CKD patients die of CVD before reaching end-stage renal disease (ESRD). Currently, researchers are trying to understand a potential bi-directional relationship between CKD and CVD," says Dr. Abhijit Kshirsagar, assistant professor of medicine at the University of North Carolina (UNC) at Chapel Hill and senior author of the paper.

"In addition, SCORED is easily accessible for self-assessment, which we believe gives it greater applicability in detecting persons at increased risk of CKD," says Dr. Kshirsagar.

SCORED can also serve as an educational tool to raise CKD awareness. The SCORED questionnaire is currently distributed via ESRD networks and the UNC Kidney Center's Kidney Education Outreach Program, and has been highlighted in Nature Clinical Practice Nephrology (2007). The researchers hope their model will be used in primary care and nephrology clinics, as well as in public health initiatives and education programs.

"We believe that screening tools such as SCORED will provide a cost-effective tool for health-care practitioners to identify individuals who are at high risk for developing CKD. The early detection of high-risk individuals is critical for both the development and implementation of strategies to prevent the progression to ESRD," says Dr. Christie M. Ballantyne, director of the Methodist DeBakey Heart Center and professor of medicine at Baylor College of Medicine in Houston.

Screening is a public health strategy for identifying an unrecognized disease in asymptomatic populations. Subjects are asked questions or offered a test to identify those individuals who are more likely to be helped than harmed by further tests or treatments that may reduce the risk of a disease or its complications. Diseases suitable for screening are those with serious consequences, those in which treatment is more effective at an earlier stage, and conditions with a long preclinical phase. CKD is deemed to fulfill these criteria; however, it is not known whether screening will in fact result in improved outcomes. The benefits of screening for CKD are yet to be determined.