Diagnosis of Chronic Kidney Disease
Chronic Kidney Disease (CKD) is diagnosed by persistent abnormalities in kidney structure or function for at least 3 months, specifically with either an estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m² or evidence of kidney damage (primarily albuminuria ≥30 mg/g). 1
Diagnostic Criteria
- CKD requires the presence of either decreased kidney function or evidence of kidney damage for at least 3 months 2, 1
- The 3-month duration requirement distinguishes CKD from acute kidney injury (AKI) 1
- Both eGFR and urine albumin-to-creatinine ratio (ACR) tests are required for comprehensive CKD screening and diagnosis 2, 1
Primary Diagnostic Tests
1. Assessment of Kidney Function
- Measure serum creatinine to calculate eGFR using standard equations such as the 2021 CKD-EPI equation 2, 1
- Initial test should be creatinine-based eGFR (eGFRcr) 2
- If more accurate assessment is needed, use combined creatinine and cystatin C-based eGFR (eGFRcr-cys) 2
- Consider direct GFR measurement using exogenous filtration markers when treatment decisions require highly accurate GFR assessment 2
2. Assessment of Kidney Damage
- Primary marker: Albuminuria measured by urine albumin-to-creatinine ratio (ACR ≥30 mg/g) in two of three spot urine specimens 1
- Secondary markers: Abnormal urinary sediment, abnormal kidney histology on biopsy, and structural abnormalities on imaging 2, 1
- Hematuria may indicate glomerular disease 2
Confirming CKD Diagnosis
Proof of chronicity (minimum 3 months) can be established by: 2
- Review of past GFR measurements
- Review of past albuminuria/proteinuria measurements
- Imaging findings (reduced kidney size, cortical thinning)
- Kidney biopsy findings (fibrosis, atrophy)
- Medical history of conditions known to cause CKD
- Repeat measurements beyond the 3-month point
Do not assume chronicity based on a single abnormal eGFR or ACR result, as it could represent acute kidney injury 2
CKD Staging
GFR categories: 1
- G1: ≥90 mL/min/1.73 m²
- G2: 60-89 mL/min/1.73 m²
- 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
Albuminuria categories: 1
- A1: <30 mg/g (normal to mildly increased)
- A2: 30-300 mg/g (moderately increased)
- A3: >300 mg/g (severely increased)
Evaluation of CKD Cause
- Establish the cause using: 2
- Clinical context and medical history (especially diabetes and hypertension)
- Personal and family history (genetic causes)
- Social and environmental factors
- Medication history (nephrotoxic drugs)
- Physical examination
- Laboratory tests
- Imaging
- Genetic and pathologic diagnosis when indicated
Laboratory Evaluation
- Complete blood count
- Comprehensive metabolic panel
- Urinalysis with microscopy
- Urine protein quantification
Additional tests based on clinical suspicion: 1
- Serologic testing for autoimmune diseases
- Complement levels
- Hepatitis B/C and HIV serology
- Serum and urine protein electrophoresis
Imaging and Kidney Biopsy
- Renal ultrasound to assess kidney size, echogenicity, and rule out obstruction 1
- Consider kidney biopsy when: 2, 1
- The cause is unclear and results would guide treatment
- Rapidly progressive disease is present
- Nephrotic syndrome is suspected
- Glomerular disease is suspected
Special Considerations
- For patients with diabetes: Type 1 diabetes - start screening 5 years after diagnosis; Type 2 diabetes - start screening at diagnosis 1
- Nephrology referral is recommended for: 2, 1
- eGFR <30 mL/min/1.73 m²
- Significant proteinuria
- Rapid decline in kidney function
- Difficulty determining the cause of CKD
- Complex management issues
Common Pitfalls in CKD Diagnosis
- Assuming a single abnormal eGFR or ACR result indicates CKD 2
- Relying solely on serum creatinine without calculating eGFR 2, 3
- Failing to test for albuminuria in high-risk patients 1, 3
- Late referral to nephrology, which is associated with worse outcomes 2
- Not considering factors that may affect creatinine-based eGFR accuracy (e.g., muscle mass, diet) 2, 4