What causes an increase in estimated Glomerular Filtration Rate (eGFR) indicating improved kidney function?

Causes of Increased eGFR (Improved Kidney Function)

An increase in estimated Glomerular Filtration Rate (eGFR) typically indicates improved kidney function and can be caused by several factors including resolution of acute kidney injury, improved blood pressure control, medication effects, lifestyle modifications, and recovery from reversible kidney conditions. 1

Normal Kidney Function and eGFR Fluctuations

Understanding eGFR changes requires context about normal kidney function:

• Normal GFR is approximately 130 mL/min/1.73 m² for men and 120 mL/min/1.73 m² for women 1
• Natural age-related decline averages 0.75 mL/min/year 1
• Small fluctuations in GFR are common and don't necessarily indicate disease progression 1

Common Causes of eGFR Improvement

1. Recovery from Acute Kidney Injury (AKI)

• AKI can temporarily reduce kidney function
• Resolution of AKI allows eGFR to return to baseline or improve
• People with diabetes are at higher risk of AKI than those without diabetes 1

2. Medication Effects

• Angiotensin Receptor Blockers (ARBs): Improve eGFR by approximately 0.4 mL/min/1.73 m²/year 2
• Statins: Contribute to eGFR improvement by 0.34 mL/min/1.73 m²/year 2
• Metformin: Associated with eGFR improvement of 0.32 mL/min/1.73 m²/year 2
• Discontinuation of nephrotoxic medications (e.g., NSAIDs) can allow kidney function to recover 1

3. Blood Pressure Control

• Improved blood pressure management reduces hyperfiltration stress on kidneys
• Optimal blood pressure control can stabilize or improve kidney function 1

4. Glycemic Control in Diabetic Patients

• Poor glycemic control can cause hyperfiltration and kidney damage
• Improved blood sugar control can stabilize or improve kidney function
• Fasting blood sugar above 7.4 mmol/L correlates with additional eGFR decline 2

5. Hydration Status

• Correction of dehydration can improve eGFR
• Proper hydration optimizes renal perfusion and function

6. Early Specialist Intervention

• Early referral to nephrology is associated with improved eGFR outcomes
• Studies show that 48.2% of CKD stage 2 patients, 29.3% of stage 3 patients, and 14.7% of stage 4 patients demonstrated significantly improved eGFR after nephrology referral 3

7. Pregnancy-Related Changes

• During normal pregnancy, GFR increases gradually to approximately 150% of normal values by the end of the first trimester 4
• This is a physiological change due to increased renal blood flow

Interpreting eGFR Changes

When evaluating eGFR increases, consider:

1. Measurement Variability: eGFR calculations have inherent variability

   • Creatinine-based equations can be influenced by muscle mass, diet, and medications 1
   • CKD-EPI is more accurate with GFR > 60 mL/min/1.73 m² 1
   • MDRD performs better with GFR < 60 mL/min/1.73 m² 1

2. Clinical Context:

   • Changes in eGFR should be interpreted alongside clinical symptoms and other markers of kidney function 1
   • The trend in creatinine or eGFR over time is often more important than absolute values 1

3. Patient Population Differences:

   • eGFR accuracy varies between populations:
     • More accurate in non-diabetic patients
     • Relatively inaccurate in diabetic patients
     • Inaccurate in living kidney donors 5

Clinical Implications

• An improving eGFR generally indicates better prognosis
• Patients with "certain rise" in eGFR have lower risk of cardiovascular events compared to those with declining kidney function 6
• The previously held idea that CKD invariably progresses is no longer valid; regression/improvement is possible with appropriate interventions 3

Monitoring Recommendations

• Assess kidney function at least annually in patients with CKD 1
• Frequency of monitoring should be based on:
  • Severity of CKD
  • Risk for progression
  • Presence of albuminuria 1
• Both albuminuria and eGFR should be monitored to enable timely diagnosis, monitor progression, and detect superimposed kidney diseases 1

Remember that while an increasing eGFR is generally positive, it's important to consider the clinical context and rule out measurement errors or other factors that might artificially affect the results.