How to Diagnose Chronic Kidney Disease
Diagnose CKD when either kidney damage markers or eGFR <60 mL/min/1.73 m² persists for ≥3 months, confirmed by repeat testing at least 3 months apart. 1, 2
Initial Testing Requirements
Test all at-risk patients simultaneously with both:
- Serum creatinine with eGFR calculation (using CKD-EPI equation) 1, 3
- Spot urine albumin-to-creatinine ratio (ACR) 1, 2
The dual testing approach is critical because either abnormality alone can establish CKD diagnosis when persistent. 1
Diagnostic Criteria (Must Persist ≥3 Months)
CKD is confirmed when any of the following persist for at least 3 months: 1, 2
- eGFR <60 mL/min/1.73 m² (even without other markers of damage) 3, 2
- ACR ≥30 mg/g (sex-specific cutpoints: >17 mg/g in men, >25 mg/g in women) 3, 2
- Other kidney damage markers: hematuria, imaging abnormalities (reduced kidney size, cortical thinning), or pathological findings (fibrosis, atrophy) 1
Confirmation Protocol
After any initial abnormal result, repeat both eGFR and ACR after at least 3 months to prove chronicity. 1, 2 This is non-negotiable—a single abnormal measurement does not establish CKD, as it could represent acute kidney injury (AKI) or acute kidney disease (AKD) rather than chronic disease. 1
Methods to Establish Chronicity: 1
- Review past eGFR measurements
- Review past albuminuria/proteinuria results
- Imaging findings (reduced kidney size, cortical thinning)
- Kidney biopsy showing fibrosis/atrophy
- Medical history of conditions causing CKD (diabetes, hypertension)
- Serial measurements spanning the 3-month threshold
eGFR Calculation Specifics
Use creatinine-based eGFR (eGFRcr) initially for all adults at risk. 1 The CKD-EPI equation is preferred over MDRD as it has less bias, especially at eGFR ≥60 mL/min/1.73 m². 3
Add cystatin C measurement (eGFRcr-cys) in specific situations: 1, 3
- When eGFRcr is 45-59 mL/min/1.73 m² without albuminuria or other damage markers (this represents 41% of U.S. patients labeled as having CKD by creatinine alone) 3
- When eGFRcr is thought to be inaccurate due to extremes of muscle mass 1, 4
- When GFR accuracy affects clinical decision-making 1
Critical Pitfalls to Avoid
Do not diagnose CKD based on a single abnormal test—this could be AKI/AKD, which requires different management. 1
Do not diagnose CKD in patients with eGFR ≥60 mL/min/1.73 m² unless documented kidney damage markers are present. 3
Do not use creatinine clearance or estimated creatinine clearance—these overestimate GFR and cause misclassification. 3
Discontinue using the term "microalbuminuria"—laboratories should report ACR values, not outdated terminology. 3
Consider dietary creatinine intake when interpreting serum creatinine levels, as this affects accuracy. 1
Establishing the Cause
Once CKD is confirmed, establish the underlying cause using: 1
- Clinical context and medical history (diabetes, hypertension, cardiovascular disease)
- Family history and genetic factors
- Social and environmental exposures
- Medication review (nephrotoxins)
- Physical examination findings
- Laboratory measures beyond eGFR/ACR
- Imaging studies
- Kidney biopsy when clinically appropriate (safe and acceptable diagnostic test) 1
When to Initiate Treatment Before Confirming Chronicity
Consider starting CKD-specific treatments at first presentation if CKD is highly likely based on clinical indicators (e.g., longstanding diabetes with retinopathy, known hypertension with left ventricular hypertrophy), even before the 3-month confirmation period. 1 This pragmatic approach prevents delays in evidence-based therapies like SGLT2 inhibitors and RAAS blockade when the diagnosis is clinically certain.