What are the diagnostic criteria and methods for Chronic Kidney Disease (CKD)?

Diagnosis of Chronic Kidney Disease (CKD)

Chronic Kidney Disease is defined as an abnormality of kidney structure or function, present for >3 months, with health consequences, and is diagnosed by persistent abnormalities in either estimated glomerular filtration rate (eGFR <60 mL/min/1.73 m²) or evidence of kidney damage (primarily albuminuria ≥30 mg/g). 1

Diagnostic Criteria

Definition of CKD

• CKD requires the presence of either decreased kidney function or evidence of kidney damage for at least 3 months 1, 2
• The 3-month duration requirement distinguishes CKD from acute kidney injury (AKI) 1

Primary Diagnostic Tests

• Both tests are required for comprehensive CKD screening and diagnosis: 1
  • Measurement of serum creatinine to calculate eGFR
  • Measurement of urine albumin-to-creatinine ratio (ACR)

Establishing Kidney Function (GFR)

• Calculate eGFR using serum creatinine and standard equations: 1
  • 2021 CKD-EPI equation (recommended, does not use race) 1
  • Modification of Diet in Renal Disease (MDRD) study equation 1
• For more accurate GFR assessment in clinical situations where eGFRcr may be less reliable:
  • Use combined creatinine and cystatin C-based eGFR (eGFRcr-cys) 1
  • Consider direct GFR measurement using exogenous filtration markers when treatment decisions require precise GFR values 1

Detecting Kidney Damage

• Primary marker: Albuminuria (ACR ≥30 mg/g) in two of three spot urine specimens 1, 2
• Secondary markers: 1, 3
  • Abnormal urinary sediment
  • Abnormal kidney histology on biopsy
  • Structural abnormalities on imaging (small echogenic kidneys, dysplastic or polycystic kidneys, renal scarring, hydronephrosis)

Confirming CKD Diagnosis

Establishing Chronicity (≥3 months)

• Proof of chronicity can be established by: 1
  • Review of past GFR measurements
  • Review of past albuminuria/proteinuria measurements
  • Imaging findings showing reduced kidney size or cortical thinning
  • Kidney biopsy showing fibrosis and atrophy
  • Medical history of conditions known to cause CKD
  • Repeat measurements beyond the 3-month point

Confirming Initial Abnormal Results

• Following detection of elevated ACR, hematuria, or low eGFR, repeat tests to confirm presence of CKD 1
• Do not assume chronicity based on a single abnormal result, as it could represent acute kidney injury 1

CKD Staging

GFR Categories (mL/min/1.73 m²)

• G1: ≥90 (Normal or high)
• G2: 60-89 (Mildly decreased)
• G3a: 45-59 (Mildly to moderately decreased)
• G3b: 30-44 (Moderately to severely decreased)
• G4: 15-29 (Severely decreased)
• G5: <15 (Kidney failure) 1

Albuminuria Categories

• A1: <30 mg/g (Normal to mildly increased)
• A2: 30-300 mg/g (Moderately increased)
• A3: >300 mg/g (Severely increased) 1

Evaluation of CKD Cause

Clinical Assessment

• Comprehensive history focusing on: 1
  • Diabetes and hypertension (predominant risk factors)
  • Family history of kidney disease
  • Medication history (especially nephrotoxins)
  • Systemic diseases associated with kidney involvement

Laboratory Evaluation

• Basic laboratory tests: 1
  • 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

• Renal ultrasound to assess kidney size, echogenicity, and rule out obstruction 1
• Additional imaging based on clinical suspicion (CT, MRI, renal angiography) 1

Kidney Biopsy

• Consider when the cause is unclear and results would guide treatment decisions 1
• Particularly useful for rapidly progressive disease, nephrotic syndrome, or suspected glomerular disease 1

Special Considerations

Diabetes-Specific Screening

• For Type 1 diabetes: Start screening 5 years after diagnosis 1
• For Type 2 diabetes: Start screening at diagnosis 1
• Annual screening with both eGFR and ACR 1

Common Pitfalls in CKD Diagnosis

• Relying solely on serum creatinine without calculating eGFR 3
• Failing to test for albuminuria (screening is underutilized) 1
• Assuming a single abnormal result indicates CKD without confirming persistence 1
• Not recognizing that early CKD is often asymptomatic (less than 5% of patients with early CKD report awareness of their disease) 3

When to Refer to Nephrology

• eGFR <30 mL/min/1.73 m² 1, 4
• Significant proteinuria (ACR ≥300 mg/g) 4
• Rapid decline in kidney function 4
• Difficulty in determining the cause of CKD 1
• Complex management issues or complications 1

By following these diagnostic criteria and evaluation steps, clinicians can effectively identify CKD early, determine its cause and severity, and implement appropriate management strategies to slow progression and reduce complications, ultimately improving patient outcomes.