What is the workup for diagnosing Chronic Kidney Disease (CKD)?

Workup for Diagnosing Chronic Kidney Disease (CKD)

The diagnosis of CKD requires both estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio (UACR) testing, with confirmation of abnormalities persisting for at least 3 months. 1

Initial Testing for CKD

Required Laboratory Tests

• Serum creatinine with eGFR calculation

  • Use CKD-EPI equation for initial assessment 1
  • Report numerical values across the full range of GFRs

• Urine albumin-to-creatinine ratio (UACR)

  • Random spot urine sample (preferred over timed collections) 1
  • Report as mg/g creatinine (avoid using term "microalbuminuria") 1

Interpretation of Initial Results

• Normal kidney function: eGFR ≥60 mL/min/1.73m² and UACR <30 mg/g
• Potential CKD: Either eGFR <60 mL/min/1.73m² or UACR ≥30 mg/g

Confirmation of CKD Diagnosis

Establishing Chronicity (≥3 months)

• Repeat abnormal tests at least once within 3 months 1
• Review past laboratory results if available
• Consider other evidence of chronicity 1:
  • Imaging findings (reduced kidney size, cortical thinning)
  • Kidney pathology findings (fibrosis, atrophy)
  • Medical history of conditions known to cause CKD

Additional Confirmatory Testing

• For borderline eGFR (45-59 mL/min/1.73m²) without albuminuria:

  • Measure cystatin C and calculate eGFRcr-cys 1
  • If eGFRcr-cys ≥60 mL/min/1.73m², CKD is less likely

• For abnormal UACR:

  • Confirm with repeat testing due to biological variability >20% 1
  • Two of three specimens should be abnormal within 3-6 months

Evaluation of CKD Cause

Clinical Assessment

• Comprehensive history focusing on:
  • Diabetes duration and control
  • Hypertension history
  • Cardiovascular disease
  • Family history of kidney disease
  • Medication review (nephrotoxic drugs)
  • Environmental and social factors 1

Laboratory Workup

• Complete blood count
• Comprehensive metabolic panel
• Lipid profile
• Urinalysis with microscopy
• Consider additional tests based on clinical suspicion:
  • Serologic testing (ANA, ANCA, complement levels)
  • Serum and urine protein electrophoresis
  • Hepatitis B, C, and HIV testing

Imaging

• Renal ultrasound to assess:
  • Kidney size and echogenicity
  • Presence of obstruction or structural abnormalities
  • Cortical thickness

Kidney Biopsy

• Consider when cause is unclear and would alter management 1
• Especially important with:
  • Rapidly declining kidney function
  • Nephrotic-range proteinuria
  • Active urinary sediment

CKD Staging and Risk Stratification

GFR Categories

• G1: ≥90 mL/min/1.73m² (normal or high)
• G2: 60-89 mL/min/1.73m² (mildly decreased)
• G3a: 45-59 mL/min/1.73m² (mildly to moderately decreased)
• G3b: 30-44 mL/min/1.73m² (moderately to severely decreased)
• G4: 15-29 mL/min/1.73m² (severely decreased)
• G5: <15 mL/min/1.73m² (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)

Common Pitfalls to Avoid

• Relying solely on eGFR without albuminuria testing 2

  • Many patients with normal eGFR have albuminuria indicating early kidney damage

• Failing to confirm abnormal results 1, 2

  • Single abnormal values may represent acute rather than chronic disease
  • Confirmation over 3 months is required for diagnosis

• Misinterpreting eGFR in certain populations 1

  • Consider cystatin C testing when creatinine-based estimates may be inaccurate:
    • Extremes of muscle mass
    • Unusual dietary patterns
    • Malnutrition
    • Obesity

• Missing non-diabetic kidney disease 2

  • Consider alternative diagnoses when:
    • Type 1 diabetes duration <5 years
    • Active urine sediment
    • Rapidly declining eGFR
    • Absence of retinopathy in type 1 diabetes

By following this systematic approach to CKD diagnosis, clinicians can accurately identify, stage, and begin appropriate management for patients with kidney disease, potentially slowing progression and reducing complications.