What is the initial assessment and management for impaired renal function?

Initial Assessment and Management of Impaired Renal Function

The initial assessment of impaired renal function should include measurement of both estimated glomerular filtration rate (eGFR) and albuminuria (UACR), as this dual assessment is essential for proper diagnosis, staging, and risk stratification of kidney dysfunction. 1

Initial Diagnostic Evaluation

Essential Laboratory Tests

• Serum creatinine (for eGFR calculation)
• Blood urea nitrogen (BUN)
• Urinary albumin-to-creatinine ratio (UACR)
• Serum electrolytes (sodium, potassium, calcium, phosphorus)
• Complete urinalysis with sediment examination

Imaging and Additional Tests

• Renal ultrasound to assess kidney size, structure, and rule out obstruction
• Consider cystatin C measurement for more accurate GFR estimation, especially in patients with borderline eGFR values 1
• Evaluate for dysmorphic RBCs, proteinuria, and cellular casts which may suggest glomerular disease 1

Risk Stratification and Staging

CKD Staging Based on eGFR 1

Stage	Description	eGFR (mL/min/1.73 m²)
1	Normal GFR with kidney damage	≥90
2	Slightly decreased GFR	60-89
3a	Mild to moderate decrease	45-59
3b	Moderate to severe decrease	30-44
4	Severe decrease	15-29
5	Kidney failure	<15 or dialysis

Risk Assessment

• Patients with lower eGFR and higher albuminuria have increased risk for:
  • Cardiovascular events
  • Kidney failure
  • Mortality 1
• Frequency of monitoring should increase with declining eGFR and increasing albuminuria 1

Management Approach

1. Blood Pressure Control

• For patients with UACR <30 mg/g: Target BP ≤140/90 mmHg 1
• For patients with UACR ≥30 mg/g: Target BP ≤130/80 mmHg 1
• First-line therapy:
  • ACE inhibitors or ARBs are preferred for patients with albuminuria >30 mg/g 1, 2
  • Monitor serum creatinine and potassium within 7-14 days after initiation 2
  • Caution: ACE inhibitors can cause acute kidney injury in patients with bilateral renal artery stenosis or volume depletion 3

2. Glycemic Control in Diabetic Patients

• Well-controlled blood glucose delays development and progression of diabetic kidney disease 1
• Consider SGLT2 inhibitors for patients with eGFR ≥20 mL/min/1.73m² to reduce CKD progression 2
• GLP-1 receptor agonists can be considered for diabetic patients with eGFR as low as 15 mL/min/1.73m² 2
• Metformin is contraindicated when eGFR <30 mL/min/1.73m² 2

3. Lifestyle Modifications

• Protein intake: Approximately 0.8 g/kg/day for patients with kidney disease 1, 2
• Sodium restriction: <2 g/day to improve BP control 2
• Weight management, smoking cessation, and regular physical activity 2

4. Medication Management

• Review all medications for potential nephrotoxicity
• Adjust medication dosages based on eGFR for renally excreted drugs 2
• Educate patients on "sick day rules" - temporarily stopping ACE inhibitors/ARBs and diuretics during acute illness with volume depletion 2
• Avoid NSAIDs and other nephrotoxic medications 2

5. Management of Complications

• Anemia: Check hemoglobin at least every 3 months; if <12 g/dL (women) or <13 g/dL (men), perform complete anemia workup 2
• Metabolic acidosis: Consider oral bicarbonate supplementation if serum bicarbonate <22 mEq/L
• Hyperkalemia: Monitor potassium levels regularly, especially in patients on RAAS inhibitors 2

Monitoring and Follow-up

Frequency of Monitoring Based on CKD Stage 2

• CKD Stage 1-2 with <1 g/day proteinuria: Every 12 months
• CKD Stage 3: Every 6 months
• CKD Stage 4 or Stage 1-2 with >1 g/day proteinuria: Every 3 months

Parameters to Monitor

• Serum creatinine, BUN, eGFR
• Electrolytes (particularly potassium)
• UACR
• Blood pressure
• Hemoglobin

Special Considerations

Acute Kidney Injury (AKI)

• All CKD patients are at increased risk for AKI 1
• Identify and treat reversible causes:
  • Volume depletion
  • Obstruction
  • Nephrotoxic medications 2
• Consider temporary discontinuation of ACE inhibitors/ARBs during acute illness 2

Advanced Planning

• Consider renal replacement therapy options when eGFR <30 mL/min/1.73m² 2
• Preserve veins suitable for potential future vascular access 2

Common Pitfalls to Avoid

1. Relying solely on serum creatinine: Creatinine can be influenced by age, gender, muscle mass, and diet 4
2. Ignoring albuminuria: Even with normal eGFR, albuminuria indicates kidney damage and increased risk 1
3. Failure to recognize non-diabetic causes: Not all kidney disease in diabetic patients is diabetic nephropathy
4. Inadequate medication adjustment: Failure to adjust medication dosages based on eGFR can lead to toxicity
5. Overlooking cardiovascular risk: CKD patients have significantly increased cardiovascular risk that requires aggressive management 5

By implementing this comprehensive approach to assessment and management, clinicians can effectively identify, stage, and treat impaired renal function, potentially slowing progression and reducing associated complications.