How do you stage Chronic Kidney Disease (CKD) as per UK guidelines?

Staging of Chronic Kidney Disease (CKD) in the UK

According to the latest UK guidelines, CKD is staged using both estimated glomerular filtration rate (eGFR) and albuminuria categories, with the combination of these two parameters providing a comprehensive assessment of kidney function and risk stratification. 1

GFR Categories (G1-G5)

GFR Category	GFR (mL/min/1.73 m²)	Description
G1	≥90	Normal or elevated
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

Albuminuria Categories (A1-A3)

Category	Albumin-to-Creatinine Ratio (mg/g)	Description
A1	<30	Normal to mildly increased
A2	30-300	Moderately increased
A3	>300	Severely increased

Key Aspects of CKD Staging

1. Diagnostic Criteria:

   • CKD is defined as abnormalities of kidney structure or function present for >3 months with implications for health 1
   • Requires evidence of either:
     • Decreased eGFR (<60 mL/min/1.73 m²) for ≥3 months
     • Evidence of kidney damage (typically albuminuria) with or without decreased eGFR

2. eGFR Assessment:

   • Use creatinine-based eGFR (eGFRcr) for initial assessment 1
   • If cystatin C is available, use the combination of creatinine and cystatin C (eGFRcr-cys) for more accurate staging 1
   • The CKD-EPI equation is preferred for eGFR calculation 1

3. Albuminuria Assessment:

   • Measured using urine albumin-to-creatinine ratio (UACR) in a random spot urine sample 1
   • Two of three specimens collected within a 3-6 month period should be abnormal before confirming albuminuria 1
   • Exercise, infection, fever, heart failure, marked hyperglycemia, and hypertension can temporarily elevate UACR 1

4. Confirming Chronicity:

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

Risk Stratification and Monitoring

The combination of GFR and albuminuria categories provides a more comprehensive assessment of risk for CKD progression, cardiovascular events, and mortality 1, 2:

• Low Risk: G1A1, G2A1
• Moderate Risk: G1A2, G2A2, G3aA1
• High Risk: G1A3, G2A3, G3aA2, G3bA1
• Very High Risk: G3aA3, G3bA2-A3, G4A1-A3, G5A1-A3

Monitoring frequency should be based on the risk category 3:

GFR and Albuminuria Category	Monitoring Frequency
Low Risk	Annually
Moderate Risk	Every 6-12 months
High Risk	Every 3-6 months
Very High Risk	Every 3 months or more frequently

Clinical Pitfalls to Avoid

1. Relying on a single measurement:

   • Do not diagnose CKD based on a single abnormal eGFR or UACR result 1
   • Recent acute kidney injury can temporarily affect results

2. Missing albuminuria testing:

   • Failure to test for albuminuria leads to missed opportunities for early intervention 4
   • Both eGFR and albuminuria are necessary for proper CKD staging and risk assessment

3. Ignoring age-related considerations:

   • While eGFR naturally declines with age, decreased GFR in elderly remains an independent predictor of adverse outcomes 3
   • Do not dismiss reduced eGFR in older adults as merely age-related

4. Overlooking non-diabetic causes of kidney disease:

   • Consider alternative or additional causes of kidney disease when seeing:
     • Active urinary sediment (red/white blood cells, cellular casts)
     • Rapidly increasing albuminuria
     • Rapidly declining eGFR
     • Absence of retinopathy (in type 1 diabetes) 1

Nephrology Referral Criteria

Based on the comprehensive CKD staging, consider nephrology referral for 3:

• eGFR <30 mL/min/1.73 m² (G4-G5)
• UACR ≥300 mg/g (A3)
• Rapid decline in eGFR (>15% per year or >5 mL/min/1.73 m² per year)
• Persistent hematuria with proteinuria
• Uncontrolled hypertension despite multiple medications
• Suspected genetic kidney disease
• Uncertainty about etiology of kidney disease

By properly staging CKD using both eGFR and albuminuria categories, clinicians can better assess risk, guide treatment decisions, and improve outcomes for patients with kidney disease.