The goal of this observational study is to investigate the impact of metabolic comorbidities on outcomes in elderly Chinese adults, through two parallel sub-cohorts: one comprising elderly individuals without chronic kidney disease (CKD) at baseline, and one comprising elderly patients with established CKD.

The main questions it aims to answer are:

Do metabolic diseases (diabetes, hypertension, hyperlipidemia, hyperuricemia, calcium-phosphorus disorders) increase the risk of incident CKD, major adverse cardiovascular events (MACE), and all-cause mortality in elderly individuals without CKD at baseline? What are the optimal diagnostic thresholds and criteria for CKD in the elderly population? How do metabolic comorbidities affect long-term outcomes - including all-cause mortality, end-stage renal disease (ESRD), and cardiovascular events - in elderly patients with established CKD? What is the comorbidity profile and disease burden of elderly CKD patients in China?

Participants in both sub-cohorts will:

Undergo baseline assessments including laboratory tests and clinical evaluations.

Provide longitudinal follow-up data through scheduled clinic visits and medical record linkage.

Contribute to a large-scale cohort of 100,000 elderly participants across multiple centers in China.

Background and Rationale Chronic kidney disease (CKD) complicated by metabolic disorders - including diabetes mellitus, hypertension, hyperlipidemia, hyperuricemia, and calcium-phosphorus disturbances - poses a significant public health threat to the elderly population. China is experiencing accelerating demographic aging, making the burden of CKD and metabolic comorbidity in older adults an increasingly pressing clinical and policy challenge.

Current clinical practice is often characterized by a fragmented approach in which multiple coexisting conditions are managed independently, without an integrated framework that accounts for their interactions. Furthermore, there is no international consensus on the diagnostic criteria, epidemiological characteristics, or prognostic assessment of CKD in the elderly.

Study Design

This is a multicenter, prospective and retrospective observational cohort study aiming to enroll a total of 100,000 elderly participants. The study comprises two sub-cohorts with distinct eligibility criteria and complementary scientific objectives:

Sub-cohort 1 - Incident CKD in Elderly Adults without CKD at Baseline:

Elderly individuals without CKD at baseline will be enrolled and followed longitudinally. Baseline and follow-up data will be collected to evaluate the impact of metabolic diseases (diabetes, hypertension, hyperlipidemia, hyperuricemia, calcium-phosphorus disorders) on the risk of incident CKD, major adverse cardiovascular events (MACE), and all-cause mortality. This sub-cohort will also be used to establish and validate age-appropriate diagnostic thresholds and criteria for CKD in the elderly Chinese population.

Sub-cohort 2 - Elderly CKD Patients with Metabolic Comorbidities:

Elderly patients with established CKD (stages 1-4, excluding stage 5 or those already on renal replacement therapy) will be enrolled. Baseline and longitudinal follow-up data will be used to characterize the comorbidity profile of elderly CKD patients in China, and to evaluate the effects of metabolic comorbidities on long-term outcomes, including all-cause mortality, progression to end-stage renal disease (ESRD), and cardiovascular events.

The objectives of this study are:

To describe the epidemiological characteristics and risk factor profiles of CKD-metabolic comorbidity in elderly adults in China.

To establish and validate age-appropriate diagnostic criteria and thresholds for CKD in the elderly.

To evaluate the prognostic impact of metabolic comorbidities on CKD-related outcomes.

To develop clinical decision-support tools applicable to community and home-based settings.

To provide evidence to inform the development and updating of relevant clinical guidelines.

For Sub-cohort 1, the inclusion and exclusion criteria are as follows:

Inclusion Criteria:

1. Baseline age ≥ 65 years.
2. Availability of baseline data on serum creatinine and at least one urinary protein measurement.
3. Urinary protein measurements include: UACR, UPCR, 24-hour urine protein quantification, and urine protein dipstick test.
4. Baseline date requirement: Between January 1, 2010, and December 31, 2025.
5. Follow-up requirement meeting at least one of the following: At least one serum creatinine measurement with an interval of ≥ 6 months after baseline. Occurrence of a primary endpoint event (new-onset CKD).

Exclusion Criteria:

Presence of CKD at baseline, defined as: Glomerular filtration rate (eGFR) < 60 ml/(min·1.73m²) or positive urine protein; or the presence of an ICD-10 diagnostic code for CKD in medical records.

For Sub-cohort 2 (CKD Patients), the inclusion and exclusion criteria are as follows:

Inclusion Criteria:

1. Baseline age ≥ 65 years.
2. Meeting the diagnostic criteria for CKD: Glomerular filtration rate (eGFR) < 60 ml/(min·1.73m²) or urine protein (UACR ≥ 30 mg/g); or based on ICD-10 codes.
3. Baseline date requirement: Between January 1, 2010, and December 31, 2025.
4. Follow-up requirement meeting at least one of the following:

Occurrence of a primary endpoint event (mortality, ESRD); At least one serum creatinine measurement with an interval of ≥ 6 months after baseline.

Exclusion Criteria:

1. End-stage renal disease (ESRD) at baseline (eGFR < 15 ml/(min·1.73m²), or prior receipt of kidney transplant or dialysis), based on ICD codes).
2. Diagnosis of acute kidney injury (AKI) within the preceding 3 months.
3. New York Heart Association (NYHA) Class III or IV heart failure or occurrence of acute myocardial infarction within the preceding 6 months.
4. Child-Pugh Class B or C liver cirrhosis.
5. Malignant neoplasm.

Participants will be recruited from multiple clinical and community-based settings across China, through a network of tertiary hospitals and affiliated community health centers.

The study population consists of elderly adults aged 60 years and older, divided into two sub-cohorts:

Sub-cohort 1: Elderly individuals without CKD at baseline, recruited from community health centers and outpatient clinics.

Sub-cohort 2: Elderly patients with established CKD, recruited from participating tertiary hospitals.

Participants are drawn from geographically diverse regions of China, contributing to a nationally representative sample of the elderly population with and without chronic kidney disease.

Individual participant data sharing is not planned at this time, due to Chinese regulations on personal information protection and human genetic resources management. Aggregated and de-identified data may be made available upon reasonable request, subject to regulatory approval.