UK Guidelines for Grading Renal Impairment Based on eGFR
According to UK guidelines, renal impairment is primarily graded based on estimated glomerular filtration rate (eGFR), with mild renal insufficiency defined as GFR 60-89 ml/min/1.73 m², moderate renal insufficiency as GFR 30-59 ml/min/1.73 m², and severe renal insufficiency as GFR 15-29 ml/min/1.73 m². 1
GFR Categories and Classification
The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines, which are followed in the UK, define the following GFR categories:
- Normal to increased GFR: G1 - GFR ≥90 ml/min/1.73 m²
- Mildly reduced GFR: G2 - GFR 60-89 ml/min/1.73 m²
- Moderately reduced GFR:
- G3a - GFR 45-59 ml/min/1.73 m²
- G3b - GFR 30-44 ml/min/1.73 m²
- Severely reduced GFR: G4 - GFR 15-29 ml/min/1.73 m²
- Kidney failure: G5 - GFR <15 ml/min/1.73 m² or treated by dialysis 1
Preferred Method for GFR Estimation
The most widely recommended method for estimating GFR in the UK is the CKD-EPI equation, which has replaced the older MDRD equation due to its better accuracy, especially at higher GFR levels 2. The equation takes into account:
- Serum creatinine
- Age
- Sex
- Race (though some centers are now moving away from race-based adjustments)
Albuminuria Categories
In addition to GFR, UK guidelines recommend assessing albuminuria to fully classify CKD:
- A1: Normal to mildly increased (ACR <30 mg/g)
- A2: Moderately increased (ACR 30-299 mg/g)
- A3: Severely increased (ACR ≥300 mg/g) 1
Complete CKD Classification
For a comprehensive assessment of kidney function, both GFR category (G1-G5) and albuminuria category (A1-A3) should be reported together. For example, a patient could be classified as CKD G3aA2, indicating moderately reduced GFR (45-59 ml/min/1.73 m²) with moderately increased albuminuria 1.
Practical Considerations
- Serum creatinine alone should not be used to grade renal impairment as it is affected by muscle mass, age, sex, and race 2
- For drug dosing purposes, eGFR may need to be converted from ml/min/1.73 m² to ml/min by multiplying by the patient's body surface area and dividing by 1.73 3
- In acute kidney injury, different criteria (RIFLE or AKIN) should be used rather than the chronic kidney disease staging 1
Clinical Applications
- Patients with eGFR <60 ml/min/1.73 m² should be evaluated for complications of CKD 1
- Patients with eGFR <30 ml/min/1.73 m² should be referred for evaluation for renal replacement therapy 1
- Certain medications require dose adjustment or are contraindicated at specific eGFR thresholds (e.g., metformin is contraindicated when eGFR <30 ml/min/1.73 m²) 4
By using this standardized approach to grading renal impairment based on eGFR, clinicians can more accurately assess kidney function, determine appropriate medication dosing, and make informed decisions about referral to nephrology services.