Definition of Chronic Kidney Disease (CKD)
CKD is defined as abnormalities of kidney structure or function present for ≥3 months, with implications for health. 1
Diagnostic Criteria
CKD is diagnosed when any one of the following persists for at least 3 months 1, 2:
1. Reduced Kidney Function
2. Markers of Kidney Damage
- Albuminuria: ACR ≥30 mg/g 1
- Urine sediment abnormalities (hematuria, pyuria) 2
- Electrolyte/tubular disorders 2
- Structural abnormalities on imaging 3, 2
- Pathological abnormalities on biopsy 2
- History of kidney transplantation 2
Critical Requirement: Persistence
The 3-month duration requirement is essential because measurements can vary within individuals over time 1. Transient abnormalities do not constitute CKD. For albuminuria specifically, two of three specimens collected within 3-6 months should be abnormal before confirming the diagnosis 4.
Key Clarifications
Why eGFR <60 mL/min/1.73 m²?
This threshold represents loss of half or more of normal adult kidney function 3. Below this level, the prevalence of CKD complications (hypertension, anemia, malnutrition, bone disease, cardiovascular disease) increases substantially 3.
Normal vs. Abnormal GFR
- Normal GFR in young adults: approximately 120-130 mL/min/1.73 m² 3
- GFR declines with age physiologically 3
- However, the definition remains the same regardless of age 3—there are no age-adjusted thresholds in current guidelines 5
Important Distinction
Patients with eGFR ≥60 mL/min/1.73 m² require evidence of kidney damage (such as albuminuria or structural abnormalities) to meet CKD criteria 1, 6. An isolated eGFR of 60-89 mL/min/1.73 m² without damage markers does not constitute CKD 6.
Classification System
Once CKD is diagnosed, it should be classified using the CGA system 6, 2:
- C = Cause (diabetes, hypertension, glomerulonephritis, etc.)
- G = GFR category (G1-G5, based on eGFR ranges)
- A = Albuminuria category (A1: <30 mg/g; A2: 30-300 mg/g; A3: >300 mg/g)
This classification system provides more precise risk stratification than GFR alone 6, 4.
Common Pitfalls
Avoid these errors:
- Diagnosing CKD based on a single abnormal test—always confirm persistence over ≥3 months 1
- Using serum creatinine alone without calculating eGFR 7
- Ignoring albuminuria when eGFR is normal or mildly reduced 1
- Assuming elderly patients with eGFR 45-59 mL/min/1.73 m² don't have "real" CKD—decreased eGFR predicts adverse outcomes regardless of age 3, 5