public health surveillance of ckd: principles, steps, and challenges

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Public Health Surveillance of CKD: Principles, Steps, and Challenges Neil R. Powe, MD, MPH, MBA, 1,2,3,4 Laura Plantinga, ScM, 2,4 and Rajiv Saran, MD, MS 5,6 Population-based surveillance of disease has become an important component of addressing such common chronic diseases as hypertension and diabetes. Such systems guide screening, prevention, and treatment resources. Development of a chronic kidney disease (CKD) surveillance system for the United States that focuses on early stages of CKD is an important activity that could help stem the increasing number of end-stage renal disease cases and CKD-related morbidity and mortality in the United States. It also could help in the evaluation of interventional programs that currently are being developed or already in place. Such a surveillance system should address the burden of CKD, awareness of CKD, CKD risk factors, CKD consequences, process and quality of care in CKD, and the health system capacity for CKD. It also should allow for estimations of the burden of CKD by age, sex, race/ethnicity, socioeconomic strata, geographic groups, and clinical subgroups. We describe the key components of a surveillance system for CKD, steps in the development of such a system, and challenges that need to be addressed. Information necessary for surveillance of CKD is evolving. At this juncture, collecting, integrating, analyzing, and interpret- ing information about CKD for surveillance by using a systematic, comprehensive, and feasible approach will be instrumental in prevention and health promotion efforts for this chronic disease. Am J Kidney Dis 53(S3):S37-S45. © 2009 by the National Kidney Foundation, Inc. INDEX WORDS : Chronic kidney disease; surveillance; epidemiology; public health. C hronic kidney disease (CKD), defined as kid- ney damage with persistent, gradual, and progressive deterioration of kidney function (loss of the ability to excrete wastes, concentrate urine, and conserve electrolytes), is a growing public health problem in the United States. Detected most commonly through laboratory measurements on blood (eg, creatinine) and urine (eg, albumin), the prevalence of its most severe stage, end-stage renal disease (ESRD), has doubled during the last de- cade, with approximately 500,000 US patients be- ing treated for ESRD in 2005. 1 Almost a decade ago, CKD was declared a focus area of the Healthy People 2010 objectives. 2 Despite the attention given to this chronic disease epidemic, there is no estab- lished comprehensive monitoring and surveillance system for the entire spectrum of CKD in the United States. Concerted efforts by the National Institute of Diabetes and Digestive and Kidney Disease (NIDDK) and the Centers for Medicare & Medicaid Services (CMS) in the establishment of the US Renal Data System (USRDS) and the ESRD Networks have historically focused on the most severe stage of CKD, stage 5 CKD or ESRD, an illness with many complications, high mortality, poor quality of life, and large health care costs. However, if we are to prevent ESRD and its related morbidity and mortality in the United States, ef- forts must be made to track the distribution of all stages of CKD, its risk factors, and consequences and identify opportunities to intervene on the ill- ness at earlier stages, particularly in high-risk groups. A surveillance system is one of the first steps in this process. We discuss the principles, steps, and challenges involved in our development of a Centers for Disease Control and Prevention (CDC)-sponsored comprehensive surveillance sys- tem for CKD in the United States. WHAT IS A SURVEILLANCE SYSTEM? A surveillance system comprehensively cap- tures and tracks all important manifestations of a disease, providing key information about disease activity, including persons affected, timing, mag- nitude, severity, and location, to guide the imple- mentation of medical and public health measures to control or contain the disease. For a chronic disease such as CKD, this means, in addition to enumeration of cases, information about progres- From the 1 Department of Medicine, Johns Hopkins Uni- versity School of Medicine; Departments of 2 Epidemiology and 3 Health Policy and Management, Johns Hopkins Bloomberg School of Public Health; 4 Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, Baltimore, MD; and 5 Depart- ment of Medicine and 6 Kidney Epidemiology and Cost Center, University of Michigan, Ann Arbor, MI. Address correspondence to Neil R. Powe, MD, Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, 2024 E Monument St, Ste 2-600, Baltimore, MD 21287. E-mail: [email protected] © 2009 by the National Kidney Foundation, Inc. 0272-6386/09/5303-0105$36.00/0 doi:10.1053/j.ajkd.2008.07.056 American Journal of Kidney Diseases, Vol 53, No 3, Suppl 3 (March), 2009: pp S37-S45 S37

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Page 1: Public Health Surveillance of CKD: Principles, Steps, and Challenges

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Public Health Surveillance of CKD: Principles, Steps, and Challenges

Neil R. Powe, MD, MPH, MBA,1,2,3,4 Laura Plantinga, ScM,2,4 and Rajiv Saran, MD, MS5,6

Population-based surveillance of disease has become an important component of addressingsuch common chronic diseases as hypertension and diabetes. Such systems guide screening,prevention, and treatment resources. Development of a chronic kidney disease (CKD) surveillancesystem for the United States that focuses on early stages of CKD is an important activity that couldhelp stem the increasing number of end-stage renal disease cases and CKD-related morbidity andmortality in the United States. It also could help in the evaluation of interventional programs thatcurrently are being developed or already in place. Such a surveillance system should address theburden of CKD, awareness of CKD, CKD risk factors, CKD consequences, process and quality ofcare in CKD, and the health system capacity for CKD. It also should allow for estimations of theburden of CKD by age, sex, race/ethnicity, socioeconomic strata, geographic groups, and clinicalsubgroups. We describe the key components of a surveillance system for CKD, steps in thedevelopment of such a system, and challenges that need to be addressed. Information necessaryfor surveillance of CKD is evolving. At this juncture, collecting, integrating, analyzing, and interpret-ing information about CKD for surveillance by using a systematic, comprehensive, and feasibleapproach will be instrumental in prevention and health promotion efforts for this chronic disease.Am J Kidney Dis 53(S3):S37-S45. © 2009 by the National Kidney Foundation, Inc.

INDEX WORDS : Chronic kidney disease; surveillance; epidemiology; public health.

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hronic kidney disease (CKD), defined as kid-ney damage with persistent, gradual, and

rogressive deterioration of kidney function (lossf the ability to excrete wastes, concentrate urine,nd conserve electrolytes), is a growing publicealth problem in the United States. Detected mostommonly through laboratory measurements onlood (eg, creatinine) and urine (eg, albumin), therevalence of its most severe stage, end-stage renalisease (ESRD), has doubled during the last de-ade, with approximately 500,000 US patients be-ng treated for ESRD in 2005.1 Almost a decadego, CKD was declared a focus area of the Healthyeople 2010 objectives.2 Despite the attention given

o this chronic disease epidemic, there is no estab-ished comprehensive monitoring and surveillanceystem for the entire spectrum of CKD in thenited States. Concerted efforts by the National

nstitute of Diabetes and Digestive and Kidneyisease (NIDDK) and the Centers for Medicare &edicaid Services (CMS) in the establishment of

he US Renal Data System (USRDS) and the ESRDetworks have historically focused on the most

evere stage of CKD, stage 5 CKD or ESRD, anllness with many complications, high mortality,oor quality of life, and large health care costs.owever, if we are to prevent ESRD and its relatedorbidity and mortality in the United States, ef-

orts must be made to track the distribution of alltages of CKD, its risk factors, and consequencesnd identify opportunities to intervene on the ill-

ess at earlier stages, particularly in high-risk

merican Journal of Kidney Diseases, Vol 53, No 3, Suppl 3 (Marc

roups. A surveillance system is one of the firstteps in this process. We discuss the principles,teps, and challenges involved in our developmentf a Centers for Disease Control and PreventionCDC)-sponsored comprehensive surveillance sys-em for CKD in the United States.

WHAT IS A SURVEILLANCE SYSTEM?

A surveillance system comprehensively cap-ures and tracks all important manifestations of aisease, providing key information about diseasectivity, including persons affected, timing, mag-itude, severity, and location, to guide the imple-entation of medical and public health measures

o control or contain the disease. For a chronicisease such as CKD, this means, in addition tonumeration of cases, information about progres-

From the 1Department of Medicine, Johns Hopkins Uni-ersity School of Medicine; Departments of 2Epidemiologynd 3Health Policy and Management, Johns Hopkinsloomberg School of Public Health; 4Welch Center forrevention, Epidemiology and Clinical Research, Johnsopkins Medical Institutions, Baltimore, MD; and 5Depart-ent of Medicine and 6Kidney Epidemiology and Costenter, University of Michigan, Ann Arbor, MI.Address correspondence to Neil R. Powe, MD, Welch

enter for Prevention, Epidemiology and Clinical Research,ohns Hopkins Medical Institutions, 2024 E Monument St,te 2-600, Baltimore, MD 21287. E-mail: [email protected]© 2009 by the National Kidney Foundation, Inc.0272-6386/09/5303-0105$36.00/0

doi:10.1053/j.ajkd.2008.07.056

h), 2009: pp S37-S45 S37

Page 2: Public Health Surveillance of CKD: Principles, Steps, and Challenges

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ion of the disease and its complications. It ismportant to distinguish surveillance from screen-ng because the 2 concepts are often confused.creening refers to identification of unrecog-ized cases of a disease. Screening may be aomponent of surveillance, but surveillance in-olves enumerating and tracking recognized casesf disease in addition to detection of unrecog-ized cases of disease.

DESIRABLE ATTRIBUTES OF ASURVEILLANCE SYSTEM

The CDC3 has proposed 7 desirable attributesor a surveillance system (Box 1). To be effectivend sustainable over time, a surveillance systemor CKD should involve relatively straightfor-ard data collection and operations for reporting

uch data on a periodic basis. It must be flexibleo examine new dimensions identified from morentensive research and accommodate changes inefinitions of disease. For example, new markersf kidney damage (eg, neutrophil gelatinase-ssociated lipocalin, dimethylarginine, and liver-ype fatty acid-binding protein)4 and kidney func-ion (eg, cystatin C) have been identified. If suchovel markers were to supersede current markersalbuminuria and creatinine) through further rig-rous testing and become commercially avail-ble, a surveillance system should be able todapt to incorporate their data collection andeporting. The data incorporated into a CKDurveillance system should be of high quality,eliable, and valid. The measures should haveonstruct validity, predictive validity, and dis-riminant validity, as well as face validity. Sourcesf data should find the system acceptable andhus be willing to participate and share their datareely. The system must be sensitive to capturevents over time and space, and a high percent-ge of true cases must be identified as possiblyaving a disease. The system must give a repre-entative picture of CKD in the United States aswhole and in communities. The system alsoust be able to report the status of CKD in a

imely fashion so that interventions can be effec-ive. Finally, some of the most important mea-ures, such as burden of kidney disease, will beost useful if data are assembled over time so

hat trends in illness can be examined. Therefore,

he sources that provide information for a CKD e

urveillance system must be stable enough tonsure that data will be available in the future. Its important to note that these attributes some-imes can be in conflict with each other; forxample, collection of data in a cohort study thatould maximize the predictive value of kidneyamage through repeated measures of albumin-ria to establish persistence may be less represen-ative than data from a geographically broaderational cross-sectional survey.

CORE STEPS IN A SURVEILLANCE SYSTEM

Design of a comprehensive surveillance sys-em for CKD includes several core steps thatarefully weigh the desirable attributes of a sur-eillance system (Box 2).5 The first step includeshe selection of important topics and measuresithin each topic area. The second includes

stablishment of indicators for each measure,long with selection of possible data sources.hird, data are collected or assembled fromources and integrated if obtained from morehan 1 data source. Fourth, data are analyzed toddress each indicator of interest. Fifth, resultsre interpreted and assembled for presentation.inally, the products of the surveillance systemre disseminated.

Ideally, the process of selecting topics andeasures to be included in a surveillance system

hould include input not only from experts, butlso from possible users of the system. For CKD,his might include representatives from the fed-

Box 1. Attributes of an Ideal Surveillance System

Simplicity of the system structure and operationFlexibility to look at new questions posed by research

and accommodate changes in technology or reportingdefinitions

Data quality for complete and valid dataAcceptability to generate enthusiasm and willingness

to participate in the systemSensitivity for capturing all events and monitoring

trendsPredictive value positive of capturing true casesRepresentativeness of the information for individuals

in the United StatesTimeliness of process from collecting information to

delivering it to make health care changesStability to reliably operate and provide information

when called upon

Adapted with permission from the CDC.3

ral government agencies impacted on by kidney

Page 3: Public Health Surveillance of CKD: Principles, Steps, and Challenges

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isease (eg, the CDC, NIDDK, CMS, Agency forealthcare Research and Quality, and Healthesources and Services Administration). Involve-ent of professional societies (eg, Americanociety of Nephrology [ASN], National Kidneyoundation [NKF], Renal Physicians Associa-

ion, American Nephrology Nurses’ AssociationANNA], American College of Physicians, andmerican Academy of Family Physicians) andatient advocacy groups (eg, American Associa-ion of Kidney Patients and American Diabetesssociation) provides input by those who can

ake local action on findings to increase aware-ess and implement change. Also, input fromocal and regional health officials can be usefuln galvanizing communities in which diseaseurden and problems are most prevalent.

A POSSIBLE CLASSIFICATION OF TOPICS FORA CKD SURVEILLANCE SYSTEM

A possible classification of topics for a surveil-ance system for CKD would include burden ofKD (incidence and prevalence), awareness ofKD, risk factors for CKD, health consequencesf CKD, processes and quality of care in CKD, andealth care system capacity for CKD. The burdenf disease should be described according to stagesf CKD (described in previous articles) and withinifferent demographic (eg, age, sex, race, and eth-icity) and clinical (eg, diabetes and hypertension)roups, across different geographic areas (eg, states),nd across time. Stage 5 CKD, or ESRD, which has

Box 2. Core Steps in the Design of aSurveillance System

Selection of topics and measures+

Identification of data sources and creation of indicators+

Data collection+

Data intergration+

Data analysis+

Interpretation of results+

Development of surveillance products+

Dissemination of products

Adapted with permission.5

een tracked since the late 1980s by its own surveil- b

ance system, the USRDS, provides an importanteference point to gauge progress in the preven-ion of kidney damage and progression ofisease. For each of these potential topics,everal measures may be relevant (Table 1),ach of which may have indicators that need toe carefully delineated (Table 2).6

POTENTIAL SOURCES OF DATA FORNATIONAL AND LOCAL SURVEILLANCE

Many types of data sources could provide rel-vant data for a CKD surveillance system. Thesenclude population-based survey data, public andrivate health care system data, screening activityata, professional societies, private industry, cohorttudies, and registries. We describe some of theseossibilities next. Table 3 lists a brief summary ofpecific data collection activities or databases forach of these types of data sources.

opulation-BasedSurveyDataNational surveys, such as the National Health

nd Nutrition Examination Survey (NHANES)nd Behavioral Risk Factor Surveillance SystemBRFSS), provide nationally representative dataor the overall health of US citizens. NHANES is

long-running national source of objectivelyeasured health and nutrition data. The NHANES

urvey, now conducted every 2 years, includeshysical examinations, clinical and laboratoryests, and personal interviews to provide a cross-ectional summary of the health and nutritionaltatus of the noninstitutionalized civilian USopulation. NHANES provides data to deter-ine rates of major diseases and health condi-

ions, as well as identify and monitor trends inedical conditions, risk factors, and emerging

ublic health issues. BRFSS is a CDC-sponsoredtate-based annual telephone survey of behav-oral risk factors with a primary purpose torovide state-specific estimates of behavioral fac-ors that contribute to the leading causes of deathn the United States. Data from the BRFSSrovide information about trends in risk behav-ors, health disparities, and effectiveness of pre-ention and education programs.

ublicHealth SystemDataPublic health programs in the United States

lso might provide useful data. The CMS serves

oth the elderly and disabled (Medicare) and
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oor (Medicaid) populations and captures alllaims from both sources. Data from the CMSould come from many sources, including theedicare Enrollment Database (EDB), Nationaledicare Utilization Database, Medicaid Utiliza-

Table 1. Examples of Measures With

Category

urden of CKD (CKDincidence and prevalence)

Prevalence of stagesIncidence of stages 1-

wareness of CKD Awareness of risk in pAwareness of risk in pAwareness of risk in thKnowledge of CKD ris

urden (incidence/prevalence)of risk factors for CKD inthose at risk

Prevalence of diabetePrevalence of hypertePrevalence of controll

ealth consequences inpatients with CKD

Proportion of patientsMortality ratesProgression of CKD bProgression of decrea

KD processes and quality ofcare

Detection of CKD in thAppropriate use of AC

and patients with hyReferral to a nephrolo

ealth system capacity forCKD

Reporting of eGFR byAdequacy of insurancUse of standardized c

Abbreviations: ACE, angiotensin-converting enzyme; ARGFR, estimated glomerular filtration rate; ESRD, end-stag

Table 2. Sample C

Field

ndicator name Prevalence of stage 3 Cemographic group Residents aged � 18 yumerator Residents aged � 18 yenominator All residents aged � 18easures of frequency Annual prevalence (aseriod for case definition 1980-2005ata resources NHANES for calculation

Bureau population esackground Estimates from NHANE

which translated to aignificance Indication of future burdimitations of indicator Requires laboratory tes

methodsimitations of dataresources

Not calculated from origfrom huge database

ddresses Healthy People2010 objectives

2010 Relevant targets iprevalent patients wit

dditional data items Individual-level data forfactors and data strat

Abbreviations: CKD, chronic kidney disease; CVD, card

SRD, end-stage renal disease; NHANES, National Health and N

ion Database (Medicaid Statistical Informationtatistics), nursing home and health assessmentata (Outcome and Assessment Information Setnd Minimum Data Set), and the Medicare Cur-ent Beneficiary Survey. The Department of Vet-

ad Categories for CKD Surveillance

Example Measures

D by eGFR (kidney function)by eGFR (kidney function)with diabeteswith hypertension

ith family history of CKD/ESRDrsus

d pressureKD moving to ESRD over time

graphic characteristics (eg, race/ethnicity)nal function by level of proteinuriath risk factorsitors/ARBs (eg, for patients with diabetes with proteinuriasion)PCP before ESRDtoriesragee

giotensin receptor blocker; CKD, chronic kidney disease;l disease; PCP, primary care physician.

dicator Template

Description

ve eGFR of 30-60 mL/min/1.73 m2

tage and estimates of number affected)

centage affected that could then be applied to Censuss for total disease burden-2000 show the prevalence of stage 3 CKD at 3.7%,ately 7.4 million US adults from 2000 Census data6

this group progresses to ESRD or CVDserum creatinine and estimation of GFR by standardized

rum creatinine measurements or will be difficult to extract

reducing the ESRD incident rate to 217/million because3 CKD have high risk of progressing to ESRD

ex, race/ethnicity, and geography for adjustment of riskn

ular disease; eGFR, estimated glomerular filtration rate;

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rans Affairs (VA), through the Veterans Healthdministration (VHA), operates the largest inte-rated health care system in the United States forll US military veterans. The VHA has a longistory of computerized clinical information sys-ems. At present, all episodes of care providednder VA auspices in VA hospitals, nursingomes, domiciles, and outpatient clinics are re-orted by facility staff using nationally distrib-ted software. The Indian Health Service (IHS),n agency within the Department of Health anduman Services, is responsible for providing

ederal health services to American Indians andlaska Natives. The IHS is the principal federalealth care provider and health advocate for theative American population. The IHS currentlyrovides health services to approximately 1.5

Table 3. Types of Data Available From

Data Source Questionnaire Examina

opulation-based surveysNHANES ✓ ✓

BRFSS ✓

ublic health systemsCMS ✓ ✓

VA ✓

HIS ✓

rivate health systemsBCBS ✓

Regional ✓

creening activitiesKEEP ✓ ✓

NKDEP ✓

rofessional societiesAMA ✓

ASN/ANNA ✓

rivate industryLabCorpQuestMedstat ✓

ohort studiesCRIC/CKiD ✓ ✓

CRIC/CKiD ✓ ✓

egistriesUSRDS ✓

SRTR ✓

Abbreviations: AMA, American Medical Association; ANNosis Risk in Communities; ASN, American Society of NeKiD, Chronic Kidney Disease in Children; CMS, Cent

nsufficiency Cohort; IHS, Indian Health Service; KEEP, Kutrition Examination Survey; NKDEP, National Kidney Dlant Recipients; VA, Veterans Affairs; USRDS, US Renal D

illion American Indians and Alaska Natives s

ho belong to more than 557 federally recog-ized tribes in 35 states.

rivateHealth SystemData

Private health insurance plans, such as Blueross Blue Shield, could provide data on aational level (in aggregate) for diagnoses, treat-ents, costs, and trends in their patient popula-

ions. Additional regional health care plans couldrovide in-depth information about trends inarticular US states or regions.

creeningActivityData

Several organizations maintain screeningnd/or educational programs that may provideseful data for CKD surveillance. The NKF

ntial CKD Surveillance Data Sources

Type of Data

Laboratory Medical Record Claims Mortality

✓ ✓

✓ ✓ ✓ ✓

✓ ✓ ✓ ✓

✓ ✓ ✓ ✓

✓ ✓ ✓ ✓

✓ ✓ ✓ ✓

✓ ✓

✓ ✓

✓ ✓ ✓ ✓

✓ ✓ ✓ ✓

✓ ✓ ✓

✓ ✓ ✓

✓ ✓ ✓

erican Nephrology Nurses Association; ARIC, Atheroscle-y; BRFSS, Behavioral Risk Factor Surveillance System;Medicare & Medicaid Services; CRIC, Chronic Renalarly Evaluation Program; NHANES, National Health andEducation Program; SRTR, Scientific Registry of Trans-stem.

Pote

tion

A, Amphrologers foridney Eisease

ponsors a free kidney health screening pro-

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ram, the Kidney Early Evaluation ProgramKEEP), designed to increase awareness aboutidney disease in high-risk individuals androvide free testing and educational informa-ion so that kidney disease and its complica-ions can be prevented or delayed. The Na-ional Kidney Disease Education ProgramNKDEP) has performed surveys on aware-ess of CKD risk factors in African Americansnd for estimated glomerular filtration rateeGFR) reporting by laboratories.

rofessional Societies

Professional societies, such as the Americanedical Association, ASN, and ANNA, alsoight provide data about issues of health care

apacity, including numbers of nephrologists andephrology nurses, in addition to nephrologyrainees.

rivate IndustryData

Private industry also may provide data usefulo CKD surveillance. For example, such nationaledical laboratories as Quest Diagnostics (Madi-

on, NJ) and LabCorp (Burlington, NC) mightave information about tests ordered and possi-ly results of tests. Private data warehouses, suchs Medstat, provide a family of databases toesearchers containing individual-level health carelaims, laboratory test results, and hospital dis-harge information from large employers, man-ged care organizations, hospitals, and Medicarend Medicaid programs.

ohort StudyData

Cohort studies, although usually not as rep-esentative as other sources, might providealuable information about the incidence androgression of disease that may be hard toapture elsewhere. For example, the Atheroscle-osis Risk in Communities (ARIC) Study7 is aongitudinal study of 15,792 participants aged5 to 64 years recruited from 4 US suburbanommunities with the primary purpose of inves-igating the cause and natural history of athero-clerosis, including determination of risk fac-ors. Baseline and follow-up visits (whichccurred every 3 years) included measure-ents of demographics, lifestyle, physiologi-

al characteristics, and laboratory measure- r

ents. Studies such as ARIC could be used totudy the incidence of CKD. Cohorts of partici-ants enrolled with kidney disease would beost useful for studying the progression of

isease. The Chronic Renal Insufficiency Co-ort (CRIC) Study8 and Chronic Kidney Dis-ase in Children (CKiD)9 are both prospectiveohort studies funded by the NIDDK of theational Institutes of Health (NIH). CRIC com-rises nearly 4,000 adult patients aged 21 to 74ears recruited from 7 centers in the Unitedtates, including Philadelphia, PA; Baltimore,D; Cleveland, OH; Chicago, IL; Ann Arbor,I; New Orleans, LA; and Oakland, CA. CRIC

ncludes measures of kidney function overime and risk factors for CKD and cardiovascu-ar disease (CVD) to examine the relationshipetween moderate stages of CKD and CVD asfirst step to prevent and better treat patientsith CKD and CVD. Selected participants alsoave undergone extensive measurement of kid-ey function with radiolabeled iothalamate.KiD is recruiting from approximately 50 cen-

ers, approximately 500 children aged 1 to 16ears who have an eGFR between 30 and 75L/min/1.73 m2. CKiD also includes mea-

ures of kidney function over time and riskactors for CKD progression to examine thempact of progression on the growth, cogni-ion, behavior, and development of risk factorsor CVD. These studies provide detailed andarefully collected data about CKD progres-ion from moderate CKD stages to ESRD.

egistryData

National registries of ESRD care (USRDS)nd transplant recipients (Scientific Registry ofransplant Recipients [SRTR]) provide valuableata. The USRDS is an NIDDK- and CMS-ponsored national database, predominantly forSRD. It provides national statistics for ESRD

ncidence and prevalence, treatment modalities,chievement of clinical indicators, and clinicalutcomes. The SRTR supports the ongoing evalu-tion of the scientific and clinical status of allolid-organ transplantations in the United States,ncluding kidney transplants. Thus, it provides aeans of following up patients who are at high

isk of CKD outcomes.

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CHALLENGES IN ESTABLISHING A CKDSURVEILLANCE SYSTEM

The processes of identifying and selectingopics and measures, identifying and selectingelevant data sources, and integrating the informa-ion into a usable surveillance system for CKD inhe United States are fraught with challenges.hese challenges include both conceptual andethod issues.

ampling

The USRDS, the current surveillance systemor ESRD, benefits from the relatively easy iden-ification of persons treated for stage 5 CKDhrough Medicare program administrative files.hus, it can enumerate nearly all cases of ESRD

n the United States and passively follow themp for such outcomes as hospitalization andeath by using Medicare program files. For earlytages of CKD, total identification of all cases isot possible. Thus, the use of NHANES data,hich uses probability sampling, has been the

ccepted approach to estimating the total burdenf CKD in the United States.10,11 Incorporatinghe sampling strategy for areas of the countryherefore is critical for appropriate analysis ofHANES data. Because NHANES has strict

onfidentiality concerns, data are not availableor smaller geographic units that might allow forocal efforts to address CKD.

stablishing aPopulationDenominator

For some data, we may be able to determinehe number of cases affected, but the largeropulation from which they come (the denomina-or) may not be clearly defined. For example,linical laboratories may be able to identify indi-iduals with CKD through creatinine measure-ents. However, these individuals represent only

hose tested, and the reasons for testing are likelyo be unknown in most cases. Similarly, healthare system data are likely to identify thoseested for CKD through proteinuria and creati-ine measurements, but CKD in individuals notested would not be identified. One could use theumber of enrollees in the health care system asdenominator, but there would be misclassifica-

ion of some persons as normal who truly have

idney disease. g

eographicDetail for State andLocal Planning

Arguably, data to compare communities withegard to CKD burden and prevention would beost useful. Many surveillance systems have

enefited from data at levels of state, county, zipode, or census tract. For CKD risk factors, itay be possible to obtain such information, but

revalence and incidence data for CKD at theocal level are hard to come by. Local efforts,uch as the New York HANES, could incorpo-ate measures for CKD in data collection toddress kidney disease in addition to other condi-ions.

tandardizationofMeasures

Some measures to calculate as part of a surveil-ance system are incidence and prevalence rates,ortality rates, and hospital admission rates.tandardization of these types of measures in aurveillance system is crucial,12 and standardiza-ion must be done to a single population at aingle time. This is to ensure that the denomina-or provides an accurate representation of CKDt all its stages by geographic area, age, race, andther patient characteristics (and eventually, overime). Many data sources provide measures thatave already been standardized to their ownopulation (eg, the reference may be state oregion level or historic).

ariableDefinitions ofMeasures

Variables such as diabetes could be defined inultiple ways, such as a self-reported diagnosis,

asting glucose level greater than 126 g/dL, orrom such information as use of diabetes medica-ion. Varying definitions such as these could giveifferent rates. In addition, GFR may be calcu-ated based on several measurements or differentormulae and thus lead to differences in classifi-ation and staging of patients with CKD.

ariability inDataQuality

Another issue is variability in the quality ofhe data because different data sources may haveifferent thresholds of quality; ie, some sourcesay release all data they have collected, whereas

ther sources might release only data that haveissing values less than a certain proportion or

hat are in sufficient numbers in demographic or

eographic subgroups that they are not identifi-
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ble. This information must be taken into ac-ount when possible. Additionally, individualeasures may have their own method issues,

uch as measurement of GFR, which may bealculated based on several measurements orifferent formulae.13-15 In this case, we ideallyould use the most recent and accepted measure-ents and formulae to estimate GFR, rather than

ecessarily depend on that calculated by the dataource.

EXTENDING CKD SURVEILLANCESYSTEMS GLOBALLY

Many countries now have registries for stage 5KD with data elements similar to the USRDS.his has allowed international comparisons inrevalence, incidence, and treatment for ESRD.1

ecause such data collection efforts can be expen-ive in countries with fewer resources, CKD dataor international comparisons will be a chal-enge. In 2006, experts from around the worldxamined CKD as a global public health prob-em initiative, addressing the issue of surveil-ance through the KDIGO (Kidney Disease: Im-roving Global Outcomes) initiative.16 Expertsrom different countries made several recommen-ations with respect to establishment of nationalKD surveillance programs (Box 3). Recogniz-

ng that data for early stages might be difficult tobtain, the group recommended that all countriesnstitute CKD surveillance, including estimatesf the prevalence of stages 4 and 5 CKD. Theyecommended that nations with resources striveo include earlier stages. In addition, they recom-ended that data for risk factors for CKD (eg,

ge, diabetes, and hypertension) and CKD pro-ression17 be included. Recognizing the effi-iency of combined efforts around CVD andKD, they suggested that surveillance for CKDe incorporated into ongoing surveillance pro-rams, and data collected that are also CKD riskactors in such programs should be used for CKDurveillance. They also made recommendationsbout topic areas, sampling, and frequency ofata collection.

CONCLUSION

Despite the large amount of work and chal-enges involved in establishing a CKD surveil-

ance system in the United States, a systematic, t

omprehensive, and feasible approach as out-ined can guide the collection, integration, analy-is, and interpretation of CKD information. Weurrently are using these principles to designomprehensive surveillance for CKD in thenited States. Such a system will be instrumen-

al in prevention and health promotion efforts forKD.

ACKNOWLEDGEMENTSSupport: Dr Powe is supported by Grant K24DK02643

rom the NIDDK.Financial Disclosure: None.

REFERENCES1. US Renal Data System: USRDS 2005 Annual Data

eport. The National Institutes of Health, National Institutef Diabetes and Digestive and Kidney Diseases, Bethesda,D, 20072. Department of Health and Human Services: Healthy

eople 2010 (ed 2). With Understanding and Improvingealth and Objectives for Improving Health. 2 vols. Wash-

ngton DC, US Government Printing Office, 20003. Updated guidelines for evaluating public health surveil-

ance systems. MMWR 50:1-35, 20014. Nickolas TL, Barasch J, Devarajan P: Biomarkers in

cute and chronic kidney disease. Curr Opin Nephrol Hyper-

Box 3. Recommendations on Surveillance From thePosition Statement From the KDIGO Controversies

Conference

All countries should have a surveillance program forCKD to estimate the prevalence of CKD stages 4-5 andstrive to include earlier stages

If possible, data for risk factors for the developmentand progression of CKD most relevant for the specificpopulation should be included

Surveillance for CKD could be incorporated into exist-ing surveillance programs and data from such programsshould be used for surveillance of CKD risk factors.

Data could be obtained from random samples of thegeneral population or (possibly) populations receivingmedical care

Data should be collected at a frequency of every 5-10y or more often, depending on disease dynamics, inter-ventional strategies, and regional resources

Additional components of a CKD surveillance pro-gram could be consequences of CKD education/aware-ness, health system capabilities, quality of care markers,and health policy goals

Abbreviations: CKD, chronic kidney disease; KDIGO,idney Disease: Improving Global Outcomes.Data from Chronic Kidney Disease as a Global Publicealth Problem: Approaches and Initiatives, Amsterdam,ctober, 2006.15

ens 17:127-132, 2008

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