What are the steps to diagnose Chronic Kidney Disease (CKD)?

Diagnosis of Chronic Kidney Disease (CKD)

To diagnose chronic kidney disease (CKD), both estimated glomerular filtration rate (eGFR) and urine albumin-to-creatinine ratio (ACR) must be measured, with abnormalities persisting for at least 3 months. 1

Definition of CKD

CKD is defined as:

• Persistent eGFR <60 mL/min/1.73 m² for ≥3 months 1, 2
• AND/OR persistent albuminuria (ACR ≥30 mg/g) for ≥3 months 1, 2
• AND/OR other evidence of kidney damage (abnormal imaging, pathology, or urinary sediment) 2

Step 1: Identify Patients for CKD Screening

Screen the following high-risk populations:

• Patients with diabetes (Type 1: start 5 years after diagnosis; Type 2: start at diagnosis) 1, 2
• Patients with hypertension 2, 3
• Patients with cardiovascular disease 3, 4
• Patients with family history of kidney failure 3

Step 2: Perform Initial Diagnostic Tests

Conduct both tests for comprehensive evaluation:

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

Step 3: Confirm Chronicity

Following detection of abnormalities, confirm persistence for ≥3 months by:

• Reviewing past measurements of eGFR and ACR 1
• Repeating tests after appropriate interval 1
• Assessing for other evidence of chronicity:
  • Imaging findings (reduced kidney size, cortical thinning) 1, 2
  • Kidney pathology showing fibrosis/atrophy 1, 2
  • Medical history of conditions known to cause CKD 1, 2

Step 4: Evaluate Cause of CKD

Establish the cause using:

• Clinical context and medical history 1
• Personal and family history 1
• Social and environmental factors 1
• Medication history (especially nephrotoxins) 2, 4
• Physical examination 1
• Laboratory tests:
  • Complete blood count 2
  • Comprehensive metabolic panel 2
  • Urinalysis with microscopy 2
  • Additional tests based on clinical suspicion (autoimmune markers, complement levels, hepatitis serology) 2
• Imaging (renal ultrasound) 2
• Consider kidney biopsy when cause is unclear and results would guide treatment 1, 2

Step 5: Stage CKD

Stage CKD based on:

1. GFR Categories:

   • G1: ≥90 mL/min/1.73 m² (normal or high)
   • G2: 60-89 mL/min/1.73 m² (mildly decreased)
   • G3a: 45-59 mL/min/1.73 m² (mildly to moderately decreased)
   • G3b: 30-44 mL/min/1.73 m² (moderately to severely decreased)
   • G4: 15-29 mL/min/1.73 m² (severely decreased)
   • G5: <15 mL/min/1.73 m² (kidney failure) 2, 5

2. Albuminuria Categories:

   • A1: <30 mg/g (normal to mildly increased)
   • A2: 30-300 mg/g (moderately increased)
   • A3: >300 mg/g (severely increased) 2, 5

Special Considerations

• For more accurate GFR assessment in clinical situations where eGFRcr may be inaccurate, use combined creatinine and cystatin C-based eGFR (eGFRcr-cys) 1
• Do not assume CKD based on a single abnormal measurement, as it could represent acute kidney injury (AKI) 1
• Early diagnosis is crucial as it leads to improved management and slowed progression of CKD 6
• Consider referral to nephrology for eGFR <30 mL/min/1.73 m², significant proteinuria, rapid decline in kidney function, or when cause is unclear 1, 2

Common Pitfalls to Avoid

• Relying solely on serum creatinine or eGFR without assessing albuminuria 1, 2
• Diagnosing CKD based on a single abnormal test result without confirming persistence 1
• Failing to consider factors that may affect creatinine-based eGFR calculations (extreme muscle mass, malnutrition) 2, 3
• Delaying diagnosis, which is associated with increased risk of CKD progression to advanced stages and adverse outcomes 6
• Not considering the full range of potential causes of CKD, which may lead to missed opportunities for specific treatments 2, 7