CKD Stage 2 and 3a Reference Ranges
CKD Stage 2 is defined as GFR 60-89 mL/min/1.73 m² with evidence of kidney damage, and Stage 3a is defined as GFR 45-59 mL/min/1.73 m². 1, 2, 3
GFR-Based Stage Definitions
Stage 2 CKD:
- GFR range: 60-89 mL/min/1.73 m² 1, 3
- Requires evidence of kidney damage (albuminuria ≥30 mg/g, proteinuria, or structural abnormalities) for diagnosis, as GFR alone is insufficient at this level 2, 3
- Represents slightly decreased GFR with kidney damage 1
Stage 3a CKD:
- GFR range: 45-59 mL/min/1.73 m² 1, 2, 3
- Can be diagnosed based on GFR alone without requiring additional evidence of kidney damage 3
- Represents mild to moderate decrease in kidney function 1
Critical Classification Requirements
Complete CKD staging requires both GFR category AND albuminuria measurement to fully assess risk and guide treatment decisions. 2, 3 The three albuminuria categories are:
- A1: <30 mg/g creatinine (normal to mildly increased)
- A2: 30-299 mg/g creatinine (moderately increased)
- A3: ≥300 mg/g creatinine (severely increased) 2, 3
The subdivision of Stage 3 into 3a and 3b is endorsed by KDIGO and KDOQI because mortality and adverse outcome risks vary significantly between these subgroups, making this distinction clinically important. 2, 3
Diagnostic Considerations
All abnormalities must persist for at least 3 months to establish chronic kidney disease and distinguish it from acute kidney injury. 2, 3 A single GFR measurement does not establish CKD without confirmation over time. 2
GFR should be estimated using prediction equations (such as CKD-EPI) that account for serum creatinine, age, sex, and race, rather than relying on serum creatinine alone. 3, 4 The CKD-EPI equation demonstrates less bias than the MDRD equation, especially at GFR ≥60 mL/min/1.73 m². 3
Clinical Implications by Stage
Stage 2 CKD management:
- Focus on early detection, CKD risk reduction, and treating comorbid conditions 3
- Annual monitoring of both eGFR and UACR is the minimum recommended frequency 2
Stage 3a CKD management:
- Medication dose adjustments are required at this GFR level, particularly for renally cleared drugs 2
- Begin evaluation for complications as GFR falls below 60 mL/min/1.73 m² 3
- ACE inhibitors or ARBs are preferred if the patient has diabetes with hypertension and any degree of albuminuria 1, 2
- At Stage 3a with normal albuminuria (A1), the patient is classified as G3a/A1, representing moderate risk requiring annual monitoring 2
- If albuminuria is elevated to A2 or A3 levels, risk increases substantially, requiring more frequent monitoring (twice to three times yearly) and consideration for nephrology referral 2
Common Pitfalls to Avoid
Avoid incomplete staging by using GFR alone. Always classify using the complete CGA system (Cause, GFR category, Albuminuria category) for proper risk stratification. 3 The combination of GFR and albuminuria provides better risk stratification for disease progression and outcomes than GFR alone. 3
Do not diagnose Stage 1 or 2 CKD based solely on GFR values. These stages require additional evidence of kidney damage such as albuminuria, proteinuria, or structural abnormalities on imaging. 2, 3