Chronic Kidney Disease Diagnosis Based on Creatinine Levels
CKD is not diagnosed by a single elevated creatinine level, but rather requires either an estimated GFR (eGFR) <60 mL/min/1.73 m² OR evidence of kidney damage (such as albuminuria ≥30 mg/g) that persists for more than 3 months. 1
Key Diagnostic Criteria
The diagnosis of CKD requires abnormalities present for >3 months with implications for health 1:
Two Pathways to CKD Diagnosis:
1. Reduced GFR Alone:
- eGFR <60 mL/min/1.73 m² (categories G3a-G5) persisting >3 months 1
- This threshold represents less than half the normal GFR in young adults (approximately 125 mL/min/1.73 m²) 1
2. Markers of Kidney Damage (with any GFR):
- Albuminuria: ACR ≥30 mg/g (≥3 mg/mmol) 1
- Urine sediment abnormalities 1
- Structural abnormalities on imaging 1
- History of kidney transplantation 1
Critical Implementation Points
Confirmation Requirements:
- Never diagnose CKD from a single measurement 1
- For albuminuria: 2 out of 3 specimens collected within 3-6 months must be abnormal due to biological variability >20% 1
- For reduced eGFR: Repeat testing to confirm persistence beyond 3 months 1
Calculating eGFR from Creatinine:
- Use the CKD-EPI equation (preferred over MDRD) for creatinine-based eGFR 1
- The CKD-EPI equation has less bias, especially at eGFR ≥60 mL/min/1.73 m² 1
Special Consideration: The Controversial Gray Zone
For patients with eGFR 45-59 mL/min/1.73 m² (G3a) WITHOUT albuminuria or other kidney damage markers:
- This represents 41% of persons estimated to have CKD in the United States 1
- Consider measuring cystatin C for confirmation, as this is an area of substantial controversy regarding disease labeling 1
- Two-thirds of persons with eGFR <60 by creatinine have CKD confirmed by cystatin C <60, and these patients have markedly elevated risks for death, cardiovascular disease, and end-stage renal disease 1
Common Pitfalls to Avoid
Transient elevations that do NOT indicate CKD:
- Exercise within 24 hours 1
- Acute infection or fever 1
- Congestive heart failure 1
- Marked hyperglycemia 1
- Recent acute kidney injury (AKI) without proven chronicity 1
Do not assume chronicity based on a single abnormal eGFR or ACR, as this could represent acute kidney injury or acute kidney disease rather than CKD 1.
Staging After Diagnosis
Once CKD is confirmed, classify by:
- GFR categories: G1 (≥90), G2 (60-89), G3a (45-59), G3b (30-44), G4 (15-29), G5 (<15) 1
- Albuminuria categories: A1 (<30 mg/g), A2 (30-300 mg/g), A3 (>300 mg/g) 1
- Cause of CKD 1
The subdivision of G3 into G3a and G3b is critical because these categories have different outcomes and risk profiles 1.