What are the diagnostic criteria for chronic kidney disease?

How to Diagnose Chronic Kidney Disease

Diagnose CKD when either eGFR <60 mL/min/1.73 m² OR albuminuria ≥30 mg/g persists for at least 3 months, confirmed by repeat testing. 1

Core Diagnostic Criteria

CKD requires both abnormal findings AND persistence for ≥3 months to distinguish from acute kidney injury: 2, 1

• Decreased kidney function: eGFR <60 mL/min/1.73 m² 2, 1
• OR evidence of kidney damage: Albuminuria (ACR ≥30 mg/g), abnormal urinary sediment, structural abnormalities on imaging, or abnormal kidney histology 1

The 3-month duration is critical—a single abnormal test does not establish CKD, as it could represent acute kidney injury or acute kidney disease. 2

Initial Diagnostic Testing

Perform both tests simultaneously for comprehensive screening: 1

• Serum creatinine to calculate eGFR using the 2021 CKD-EPI equation 2, 1
• Urine albumin-to-creatinine ratio (ACR) on a spot urine sample 1

For men, ACR >17 mg/g is abnormal; for women, ACR >25 mg/g is abnormal. 2 However, the standard threshold of ≥30 mg/g is used for CKD diagnosis. 1

Confirming Chronicity

After detecting an abnormality, establish persistence through: 2, 1

• Review of past laboratory records showing previous abnormal eGFR or albuminuria
• Repeat measurements at or beyond the 3-month point
• Imaging findings suggesting chronic changes (small kidneys, cortical thinning, cysts)
• Medical history indicating long-standing diabetes, hypertension, or other risk factors
• Kidney biopsy showing chronic histologic changes

Critical caveat: Do not assume chronicity from a single test. However, if CKD is highly likely based on clinical context (e.g., long-standing diabetes with retinopathy), consider initiating CKD-specific treatments at first presentation while confirming chronicity. 2

Refining GFR Assessment

Use this algorithm when eGFR accuracy is questioned: 2

1. Initial assessment: Calculate eGFR from serum creatinine (eGFRcr)
2. If accuracy concerns exist (extremes of muscle mass, malnutrition, amputation): Measure cystatin C and calculate eGFRcr-cys (combined creatinine-cystatin C equation) 2
3. If even greater accuracy needed (e.g., potential living kidney donor): Measure GFR directly using exogenous filtration markers 2

Establishing the Cause

Essential History Elements 2, 1

• Diabetes duration and control: Type 1 diabetes typically develops CKD after 10 years; Type 2 may have CKD at diagnosis 3
• Hypertension history and control 2
• Family history: Construct a pedigree for polycystic kidney disease, Alport syndrome, or other genetic causes 2
• Medication exposure: NSAIDs, lithium, calcineurin inhibitors, aminoglycosides 2
• Systemic disease symptoms: Rash, joint pain, sicca symptoms suggesting autoimmune disease 2

Basic Laboratory Evaluation 1

• Complete blood count
• Comprehensive metabolic panel (electrolytes, calcium, phosphate, bicarbonate)
• Urinalysis with microscopy: Hematuria suggests glomerulonephritis; pyuria suggests interstitial nephritis; oval fat bodies suggest nephrotic syndrome 2
• Hemoglobin A1c (if diabetic or at risk)

Additional Testing Based on Clinical Suspicion 2, 1

• Serologic tests: Anti-PLA2R (membranous nephropathy), ANCA (vasculitis), anti-GBM antibodies (Goodpasture), complement levels (lupus, post-infectious GN)
• Serum and urine protein electrophoresis/immunofixation: For suspected myeloma or monoclonal gammopathy of renal significance 2
• Genetic testing: APOL1 (African ancestry with FSGS), COL4A3/4/5 (Alport syndrome), PKD1/PKD2 (polycystic kidney disease), particularly when family history is atypical 2

Imaging 2, 1

Perform renal ultrasound to assess: 1

• Kidney size (small kidneys suggest chronicity; normal or large kidneys occur in diabetes, amyloidosis, HIV-associated nephropathy, polycystic kidney disease)
• Echogenicity (increased suggests chronic parenchymal disease)
• Obstruction (hydronephrosis)
• Cysts or masses

Important pitfall: Normal-sized kidneys with preserved corticomedullary differentiation do NOT exclude CKD, particularly in diabetic kidney disease, minimal change disease, early FSGS, or infiltrative disorders. 3

Kidney Biopsy 2

Consider biopsy when: 2, 1

• Cause is unclear and results would change management
• Rapidly progressive kidney function decline
• Nephrotic-range proteinuria (>3.5 g/day)
• Active urinary sediment with RBC casts
• Suspected glomerular disease requiring immunosuppression
• Diabetic patients with atypical features (short diabetes duration, absence of retinopathy, hematuria, rapid decline)—up to 30% have non-diabetic causes 3

CKD Staging

Classify by both GFR category and albuminuria category: 1, 4

GFR Categories:

• G1: ≥90 mL/min/1.73 m² (with evidence of kidney damage)
• G2: 60-89 mL/min/1.73 m² (with evidence of kidney damage)
• G3a: 45-59 mL/min/1.73 m²
• G3b: 30-44 mL/min/1.73 m²
• G4: 15-29 mL/min/1.73 m²
• G5: <15 mL/min/1.73 m² (kidney failure)

Albuminuria Categories:

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

Screening Recommendations

High-Risk Populations Requiring Screening 1, 5

• Type 1 diabetes: Begin screening 5 years after diagnosis 1
• Type 2 diabetes: Screen at diagnosis, then annually with both eGFR and ACR 1, 3
• Hypertension 5
• Cardiovascular disease 5
• Family history of kidney disease 5
• Age >60 years (17% have eGFR <60) 2

Nephrology Referral Criteria

Refer when: 1, 4, 5

• eGFR <30 mL/min/1.73 m² (Stage 4 or 5) 1, 4
• Albuminuria ≥300 mg/g 5
• Rapid eGFR decline (>5 mL/min/1.73 m²/year) 1
• Difficulty determining CKD cause 1
• Complex management issues (resistant hypertension, refractory electrolyte abnormalities) 1

Critical pitfall: Late nephrology referral (shortly before dialysis) is associated with increased morbidity and mortality. Refer all Stage 4 patients. 2, 4

Common Diagnostic Pitfalls

• Equating creatinine clearance with GFR: Creatinine clearance overestimates GFR; always use eGFR equations 6
• Diagnosing CKD in patients with eGFR ≥60 without evidence of kidney damage: eGFR ≥60 alone is NOT CKD unless accompanied by albuminuria or other markers of kidney damage 6
• Assuming normal kidney size excludes CKD: Diabetic kidney disease, early FSGS, and infiltrative diseases maintain normal kidney size 3
• Single abnormal test: Always confirm with repeat testing before labeling a patient with CKD 2