For a patient with a history of kidney stones and an estimated Glomerular Filtration Rate (eGFR) of 64 mL/min/1.73 m², does this fall under Chronic Kidney Disease (CKD) stage 2 or stage 3a using the combined equation?

CKD Staging: eGFR 64 mL/min/1.73 m² Classification

You are correct—an eGFR of 64 mL/min/1.73 m² falls in CKD Stage 2, not Stage 3a, but only if there is evidence of kidney damage present. 1, 2

Understanding the CKD Staging System

The confusion likely stems from incomplete understanding of how CKD stages 1 and 2 differ from stages 3-5:

Stage 2 CKD Definition

• Stage 2 requires BOTH an eGFR of 60-89 mL/min/1.73 m² AND evidence of kidney damage (such as albuminuria ≥30 mg/g, proteinuria, hematuria, or structural abnormalities on imaging) 1, 2
• Without evidence of kidney damage, an eGFR of 64 does not meet criteria for any CKD stage 1

Stage 3a CKD Definition

• Stage 3a is defined as eGFR 45-59 mL/min/1.73 m² 1, 2, 3
• At this stage, the reduced eGFR alone is sufficient for diagnosis, regardless of whether kidney damage markers are present 1, 2

Critical Distinction Between Early and Later CKD Stages

Stages 1-2 require evidence of kidney damage PLUS the eGFR criteria, while stages 3-5 can be diagnosed by eGFR alone. 1, 2

For Your Patient with eGFR 64:

• If albuminuria is present (UACR ≥30 mg/g) or other kidney damage markers exist: Stage 2 CKD 1
• If no evidence of kidney damage: No CKD diagnosis despite the eGFR value 1
• The history of kidney stones alone does not constitute evidence of kidney damage unless there are persistent abnormalities in kidney structure or function 4

Complete CKD Classification Requirements

Modern CKD classification requires assessment of three components: Cause, GFR category, and Albuminuria category (CGA classification). 2, 3

Albuminuria Categories:

• A1: <30 mg/g (normal to mildly increased) 3
• A2: 30-299 mg/g (moderately increased) 3
• A3: ≥300 mg/g (severely increased) 3

Risk Stratification at eGFR 64:

• With normal albuminuria (A1): Low risk, minimal intervention needed 3
• With A2 albuminuria: Moderate risk requiring closer monitoring 3
• With A3 albuminuria: High risk requiring nephrology evaluation 3

Common Pitfall to Avoid

The most common error is diagnosing CKD based on a single eGFR measurement or assuming any eGFR <90 automatically indicates CKD. 2, 5 All abnormalities must persist for at least 3 months to distinguish chronic from acute kidney disease, and stages 1-2 absolutely require evidence of kidney damage beyond just the eGFR value. 2, 5, 6