What are the recommendations for managing impaired renal function?

Management of Impaired Renal Function

The management of impaired renal function requires monitoring kidney function regularly, controlling blood pressure, reducing proteinuria, avoiding nephrotoxic agents, and adjusting medications based on GFR levels. 1, 2

Assessment of Kidney Function

Initial Evaluation

• Estimate glomerular filtration rate (GFR) using creatinine-based equations
  • CKD-EPI equation is recommended over MDRD Study equation due to less bias and greater accuracy 1
  • Consider cystatin C measurement for more accurate GFR estimation, especially when eGFRcreat is 45-59 ml/min/1.73 m² 1
• Screen for albuminuria/proteinuria using:
  • Urine dipstick analysis (initial screening)
  • Spot urine albumin-to-creatinine ratio (ACR) or protein-to-creatinine ratio for quantification 1
• Perform renal ultrasound to assess kidney size and structure when CKD is detected 1

Classification of CKD

CKD is classified based on cause, GFR category, and albuminuria category 1:

GFR Category	GFR Range (mL/min/1.73 m²)	Description
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

Monitoring Recommendations

Frequency of Monitoring

• Monitor GFR and albuminuria based on risk category:
  • Higher risk (higher albuminuria or lower GFR): More frequent monitoring (every 3-6 months)
  • Lower risk: Less frequent monitoring (annually) 1, 2
• Check serum creatinine, BUN, and eGFR within 1-2 weeks after medication changes 2
• Monitor elderly patients with declining GFR more frequently (every 1-3 months) 2

Electrolyte Monitoring

• Monitor serum potassium closely, especially after medication changes 2
• Check serum sodium, as certain medications can cause hyponatremia 2
• Evaluate for mineral bone disease (calcium, phosphate, vitamin D) 2
• Monitor for metabolic acidosis and treat if serum bicarbonate <22 mmol/L 2

Treatment Strategies

Blood Pressure Management

• Target blood pressure ≤140/90 mmHg for patients with urine albumin excretion <30 mg/24 hours 1
• Target blood pressure ≤130/80 mmHg for patients with urine albumin excretion ≥30 mg/24 hours 1
• Use ACE inhibitors or ARBs as first-line therapy, especially with albuminuria >300 mg/24 hours 1, 2
• Consider replacing thiazide diuretics with loop diuretics when GFR <45-50 ml/min/1.73 m² 2

Medication Management

• Maintain ACE inhibitor or ARB therapy despite modest increases in serum creatinine (up to 30%) 2
• Avoid dual RAS blockade (combining ACEi with ARB) due to increased risk of hyperkalemia and acute kidney injury 2
• Adjust medication dosages based on GFR, especially for drugs with renal clearance 2
• Avoid nephrotoxic agents when possible, including NSAIDs and certain antibiotics 2

Lifestyle Modifications

• Restrict dietary sodium to <2.0 g/day 2
• Limit protein intake to 0.8 g/kg/day for patients with GFR <60 ml/min/1.73 m² and proteinuria 2
• Target caloric intake of 30-35 kcal/kg/day, emphasizing plant-based protein sources 2
• Normalize weight, stop smoking, and exercise regularly 2

Special Considerations

High-Risk Populations

• African American persons, patients with diabetes, hypertension, hepatitis C virus coinfection, and HIV patients with CD4+ counts <200 cells/mL require more vigilant monitoring 1
• HIV-infected patients should be screened for kidney disease at diagnosis and annually if at high risk 1

Referral to Nephrologist

Consider referral when:

• Abnormal kidney function persists
• Progressive decline in kidney function occurs
• Significant proteinuria is present
• Specialized diagnostic procedures (e.g., kidney biopsy) are needed 1

Common Pitfalls to Avoid

• Relying solely on serum creatinine: Serum creatinine alone is inadequate for assessing kidney function as it can be affected by muscle mass, diet, and other factors 1, 3
• Misinterpreting small GFR changes: Small fluctuations in GFR are common and don't necessarily indicate progression; consider both change in GFR category and percentage change (≥25%) 1
• Discontinuing ACEi/ARB prematurely: A modest increase in serum creatinine (up to 30%) is expected with ACEi/ARB therapy and should not prompt discontinuation unless severe 2
• Overlooking cardiovascular risk: Patients with CKD have significantly increased cardiovascular risk and require appropriate risk factor management 2

By following these evidence-based recommendations, clinicians can effectively manage impaired renal function, slow disease progression, and reduce the risk of complications.