Chronic kidney disease (CKD) is a silent epidemic affecting more than 37 million Americans. The burden of morbidity and mortality associated with CKD derives from its frequent progression to end-stage kidney disease (ESKD) and the disproportionate risk of cardiovascular disease (CVD) and associated complications. CKD is strongly and independently associated with CVD, even after adjustment for traditional CVD risk factors. This led to the hypothesis that other risk factors augment the rate of CVD in the setting of CKD. Hence, many patients with progressive renal disease succumb to fatal CVD events before they need renal replacement therapy.

The National Institute of Diabetes, Digestive, and Kidney Diseases (NIDDK) established the Chronic Renal Insufficiency Cohort (CRIC) Study in 2001 with the initial goal of elucidating the relationship between CKD and CVD. Since its inception, the CRIC Study has recruited and followed a racially and ethnically diverse cohort of over 5,000 participants with reduced kidney function from 13 clinical recruitment sites across the US. The original aim of CRIC was to establish a clinical research laboratory designed to (a) identify novel predictors of CKD progression, and (b) characterize the manifestations of CVD and identify its risk factors among individuals with CKD. The CRIC Study has examined a broad set of etiological factors (clinical, behavioral, and biomarker-associated) potentially responsible for both progressive CKD and CKD-related morbidities, especially those early in the course of CKD. Characterizing relationships between these risk factors and outcomes should facilitate identification of high-risk subgroups with CKD and guide enrollment into preventive treatment trials and application of preventive therapies. Over time, the scientific focus and the CRIC investigator network have broadened extensively through a highly successful ancillary studies program that has included more than 100 projects, most of which have been funded through federal grants. To date, the CRIC Study's investigative activities have resulted in over 300 published scientific papers with many additional manuscripts in development.

Study Visits and Participant Contact

During its 5th and final phase, the 7 Clinical Centers comprised of 12 sites will extend participant follow-up for participants who have not reached ESKD before the inception of Phase 5 by conducting 2 study visits. For all participants, Visit 1 is conducted in person at the study site. Visit 2 can be conducted in person or by telephone. For participants who enrolled in one or more Phase 4 subprotocols, Visit 2 requires a blood draw for a creatinine measurement. The blood draw can be performed at the study site, at a commercial laboratory, or at the participant's home. The principal focus for these study visits is to ascertain kidney and clinical CVD outcomes, both of which are of particular importance for the participants who enrolled in the three Phase 4 subprotocols. Participants may be contacted at other times during the year to answer additional questions or to join ancillary studies. Participants who are known by the study team to have ESKD will not have any in-person visits or scheduled telephone calls.

Phase 5 Visit 1

Participants without ESKD will complete one initial visit through the end of 2024 (Visit 1) and one follow up visit during the following year (Visit 2). Data collection has been streamlined in accordance with the Phase 5 objectives . At the in-person visit, informed consent will be obtained for continued participation in the CRIC Study. Blood pressure, weight, and medical history data will be obtained using standardized equipment and protocols established previously in the CRIC Study. Blood and urine samples will be collected for serum creatinine, serum cystatin C, and urine protein/creatinine, the key indicators of kidney outcomes. Serum creatinine will be measured locally using CLIA-approved laboratories, and serum cystatin C and urine protein/creatinine will be measured at the CRIC Central Laboratory (CCL) at the University of Pennsylvania. As has been done in earlier phases, the results of the serum creatinine measurement will be provided to participants. Serum and urine remaining after the centralized measurements will be stored at the CCL during the Phase 5 award period for potential analyses in the future. For participants who are unable to come to the Clinical Center for an in-person visit, informed consent and the medical history and hospitalization data will be obtained by telephone. Participants should be encouraged to get blood drawn at a laboratory or at their home if they are not able to come to the Clinical Center.

Phase 5 Visit 2

The follow-up visit for participants without ESKD can take place by telephone or in person. During the follow-up visit, medical history updates and hospitalization data will be collected.

The subset of participants who participated in any of the three Phase 4 subprotocols will be asked to have a second blood draw for creatinine measurement at or around the time of Visit 2. The creatinine measurement can be performed at the study site, at a commercial laboratory, or at the participant's home.

Follow-up of Participants who have Reached ESKD

Participants who have reached ESKD before the start of Phase 5 will not have in person visits but will be consented via a telephone visit for passive follow-up through linkages with the US Renal Data System, the National Death Index, and other national billing claims or other databases. These participants will also be asked to consent to sharing their contact information with the SDCC to facilitate potential future studies. Sharing of contact information is not required for participation in Phase 5. While participants who have reached ESKD will not undergo in-person visits as part of the core CRIC Phase 5 protocol, they may be invited to complete additional visits/activities for ancillary studies.

Close Out Activities

During the 3 years of the Clinical Center Phase 5 funding period, the Clinical Centers will hold local events to express appreciation to study participants for their contribution over many years and to provide them with an overview of major findings. The last 6 months of the Clinical Center funding period will focus on closeout activities including resolution of data queries, storage of study documents, and regulatory reporting and completion of outcome ascertainment.

Inclusion Criteria:

During the screening visit a blood sample will be tested to indirectly check kidney function based on the serum creatinine level:

• Age Range: 21 - 79 years
• Estimated Glomerular Filtration Rate (GFR): 45 - 70 mL/min/1.73m²
• Proteinuria: varies dependent on eGRF

Exclusion Criteria:

• Unable or unwilling to provide informed consent
• Previously received dialysis (peritoneal and/or hemodialysis) lasting more than one month
• Prior organ or bone marrow transplant
• Prior renal transplant
• Received immunosuppressive or other immunotherapy for primary renal disease or systemic vasculitis that affects the kidneys (i.e., anti-GCM, ANCA, SLE, IgA nephropathy, cryoglobulin, etc.) within the past six months before enrollment
• Received chemotherapy or alkylating agents for systemic cancer
• Known cirrhosis
• NYHA Class III or IV heart failure at baseline
• Previous diagnosis of multiple myeloma or renal carcinoma
• Previously diagnosed polycystic kidney disease
• Known HIV infection and/or AIDS
• Pregnant or breast-feeding women
• Currently participating in an interventional clinical trial (i.e., primarily trials of therapeutic agents that may have an effect on renal or cardiovascular outcomes).
• Institutionalized (e.g., prisoner, nursing home resident, skilled nursing facility resident)
• Appears unlikely or unable to participate in the required study procedures as assessed by the investigator, study coordinator or designee.

In Phase I of the CRIC Study a total of 3,939 individuals across the spectrum of severity of kidney disease were enrolled to ensure that a sufficient number of patients reach the primary study endpoints of kidney disease progression and cardiovascular events. During CRIC Phase III, an additional 1,560 older participants with milder severity of kidney disease were recruited. The 1,560 new cohort members, compared with participants recruited in Phase I, have higher ranges of age and more preserved kidney function, and most have proteinuria. The population of 1560 new recruits have similar characteristics as the current CRIC cohort: ~50% with Diabetes, ~50% female, ~45% white and ~45% African-American.