KDIGO Chronic Kidney Disease (CKD) Classification and Diagnostic Guidance

1. CKD Classification Framework

• The KDIGO guideline defines CKD using a three‑component “CGA” system: Cause, GFR category (G), and Albuminuria category (A). 1

2. GFR Category Definitions (KDIGO)

• G1 and G2 definitions are based on KDIGO 2013 recommendations. 1
• G3a and G3b definitions are from the same KDIGO source. 2
• G5 definition (including dialysis) is supported by KDIGO‑endorsed evidence. 3

3. Core Diagnostic Requirements

• CKD is diagnosed only when renal abnormalities persist for > 3 months and have clinical implications. 1
• For a G2 eGFR (60–89), evidence of kidney damage is mandatory, which may be demonstrated by any of the following:
• In the absence of such damage, an isolated eGFR of 64 mL/min/1.73 m² does not meet CKD criteria. 1

4. Albuminuria Assessment (American Diabetes Association)

• Measurement of urine albumin‑to‑creatinine ratio (UACR) is required to complete the CGA classification. 5
• UACR categories:
• For patients with diabetes, annual albuminuria screening is recommended; confirmation of persistent albuminuria requires two of three abnormal specimens collected within 3–6 months. [5][6]4

5. Confirmatory Testing When eGFR Is Borderline

• If eGFR falls into the G3a range (45–59) without albuminuria or other damage markers, measurement of cystatin C is advised to clarify CKD status. 2
• Approximately two‑thirds of individuals with creatinine‑based eGFR < 60 mL/min/1.73 m² are confirmed to have CKD when cystatin C is added. 2

6. Age‑Related Interpretation of GFR

• GFR naturally declines with age; a value of 64 mL/min/1.73 m² may reflect normal aging rather than disease. 1
• Nevertheless, an eGFR < 60 represents < 50 % of the young adult normal (~125 mL/min/1.73 m²) and is associated with increased risk of complications irrespective of age. 1

7. Preferred eGFR Equation (KDIGO)

• The CKD‑EPI equation is the recommended method for estimating GFR from serum creatinine, offering less bias than the MDRD equation, especially when eGFR ≥ 60 mL/min/1.73 m². 2

8. Monitoring Frequency

• Repeat serum creatinine and eGFR within 3 months to verify chronicity of any abnormality. 1
• Once CKD is confirmed with albuminuria, annual monitoring is advised; if treatment targets are not met, monitoring may increase to up to four times per year. 3

9. Nephrology Referral Triggers (American Diabetes Association)

• eGFR < 30 mL/min/1.73 m² (Stage G4 or worse) 3
• Progressively increasing albuminuria 4
• Continuously declining eGFR 4
• Uncertainty regarding the underlying kidney disease etiology 5
• Rapidly progressive kidney disease 4

*An eGFR of 64 mL/min/1.73 m² alone does not meet these referral thresholds unless additional concerning features are identified. [5][4]6

Interpretation of eGFR 60–89 mL/min/1.73 m² in Adults (KDIGO Guidance)

Definition and Classification

• KDIGO classifies an eGFR of 60–89 mL/min/1.73 m² as category G2 (“mildly decreased GFR”). This categorization alone does not constitute chronic kidney disease (CKD) without evidence of kidney damage persisting > 3 months. 7

Expected Normal Values

• In healthy young adults the average GFR is ≈ 125 mL/min/1.73 m²; an eGFR of 72 mL/min/1.73 m² therefore represents roughly 58 % of the expected normal function. 7

Diagnostic Requirements for CKD

• CKD is confirmed only when albuminuria (UACR ≥ 30 mg/g) or another marker of kidney damage (e.g., imaging abnormalities, hematuria, tubular dysfunction) is present together with a G2 eGFR, resulting in a classification of G2A2 (or G2A3 if albuminuria is severe). 7

Risk Stratification

• When eGFR = 72 mL/min/1.73 m² and albuminuria is absent, the patient’s risk for adverse kidney and cardiovascular outcomes is considered low. 7

Follow‑Up Recommendations for Patients Without Documented Damage

• If no kidney damage is identified, repeat eGFR measurement annually in individuals with risk factors such as diabetes, hypertension, or a family history of kidney disease. 8

Management Interventions When CKD Is Confirmed

• For patients with confirmed CKD (e.g., albuminuria present), KDIGO recommends kidney‑protective measures including:

Clinical Pitfalls to Avoid

• Do not diagnose CKD solely on a single G2 eGFR value without confirming persistent kidney damage. 7
• Do not attribute a G2 eGFR in a 42‑year‑old to normal age‑related decline; further evaluation for damage is required. 7
• Albuminuria testing is mandatory in the diagnostic work‑up of a G2 eGFR. 7
• Nephrology referral is not indicated at eGFR = 72 mL/min/1.73 m² unless there is progressive decline, worsening albuminuria, or diagnostic uncertainty. 8