At what estimated Glomerular Filtration Rate (eGFR) should I be concerned about Acute Kidney Injury (AKI)?

When to Worry About Acute Kidney Injury Based on eGFR

An eGFR below 45 mL/min/1.73 m² should raise concern for acute kidney injury (AKI) risk, with significantly increased risk when eGFR falls below 30 mL/min/1.73 m². 1 This threshold represents the point where patients are considered to have impaired kidney function relevant to toxin clearance and are at substantially higher risk for complications.

Understanding AKI Risk Based on eGFR

The KDOQI guidelines define impaired kidney function relevant to toxin clearance and AKI risk as:

1. Advanced stage 3b, 4, or 5 chronic kidney disease (eGFR <45 mL/min/1.73 m²) 1
2. Stage 2 or 3 acute kidney injury from the KDIGO classification 1
3. Serum creatinine ≥176 μmol/L (2 mg/dL) in adults without baseline values 1
4. Presence of oligo/anuria for >6 hours, regardless of serum creatinine 1

AKI Staging and Monitoring

AKI is classified into three stages according to KDIGO guidelines:

Stage	Creatinine Criterion	Urine Output Criterion
1	Increase ≥0.3 mg/dL in 48h or 1.5-1.9× baseline	<0.5 mL/kg/h for 6-12h
2	2.0-2.9× baseline	<0.5 mL/kg/h for ≥12h
3	≥3.0× baseline or increase to ≥4.0 mg/dL or RRT initiation	<0.3 mL/kg/h for ≥24h or anuria for ≥12h

1, 2

Risk Stratification Based on eGFR

• eGFR <45 mL/min/1.73 m²: Begin monitoring for AKI risk; consider medication adjustments 1
• eGFR 30-44 mL/min/1.73 m²: Review and potentially adjust nephrotoxic medications (e.g., metformin) 1
• eGFR <30 mL/min/1.73 m²: High risk for AKI; discontinue nephrotoxic medications and consider preventive measures 1, 2

Clinical Implications of Low eGFR

1. Medication Management:

   • Temporarily discontinue potentially nephrotoxic drugs in patients with eGFR <60 mL/min/1.73 m² during serious illness 1
   • These include RAAS blockers (ACE inhibitors, ARBs), diuretics, NSAIDs, metformin, lithium, and digoxin 1
   • Metformin should be reviewed when eGFR is 30-44 mL/min/1.73 m² and discontinued when <30 mL/min/1.73 m² 1

2. Contrast Studies:

   • eGFR <30 mL/min/1.73 m² represents significant risk for contrast-induced AKI 1
   • Consider alternative imaging or preventive measures when eGFR <45 mL/min/1.73 m² 1

3. Monitoring Requirements:

   • More frequent monitoring of kidney function when eGFR <45 mL/min/1.73 m² 1, 2
   • Daily monitoring may be warranted when eGFR <30 mL/min/1.73 m² 2

Prognostic Significance

Research shows that AKI risk increases substantially with decreasing eGFR:

• 8.9% risk with eGFR ≥60 mL/min/1.73 m²
• 68.9% risk with eGFR <30 mL/min/1.73 m² 3

The combination of low baseline eGFR and AKI significantly increases mortality risk and progression to end-stage renal disease 3, 4.

Important Caveats

1. Fluctuating Kidney Function: In critically ill patients, standard eGFR equations may overestimate kidney function 5

2. Baseline Creatinine Issues: When baseline creatinine is unknown, estimated baseline values may lead to misdiagnosis of AKI in up to 42% of cases 6

3. Kinetic eGFR: A decrease in kinetic eGFR ratio >10% may predict AKI approximately 24 hours before laboratory detection 7

4. Comorbidities: Diabetes, heart failure, and other conditions significantly increase AKI risk at any eGFR level 2

In summary, while any decrease in eGFR warrants attention, an eGFR below 45 mL/min/1.73 m² should trigger increased vigilance, with particularly aggressive monitoring and preventive measures implemented when eGFR falls below 30 mL/min/1.73 m².