Initial Workup for Patients with Impaired Renal Function (Low eGFR)
The initial workup for a patient with impaired renal function should include assessment of eGFR and albuminuria, evaluation for reversible causes, and consideration of referral to a nephrologist based on severity, progression rate, and associated complications. 1
Step 1: Confirm and Classify CKD
- Verify low eGFR with at least two measurements 90-730 days apart 2
- Classify CKD stage based on eGFR level 1:
- Stage 1: ≥90 mL/min/1.73 m² with kidney damage
- Stage 2: 60-89 mL/min/1.73 m² with kidney damage
- Stage 3a: 45-59 mL/min/1.73 m² (mild to moderate decrease)
- Stage 3b: 30-44 mL/min/1.73 m² (moderate to severe decrease)
- Stage 4: 15-29 mL/min/1.73 m² (severe decrease)
- Stage 5: <15 mL/min/1.73 m² or dialysis (kidney failure)
Step 2: Assess for Kidney Damage and Progression
- Measure urinary albumin/creatinine ratio (UACR) 1
- Define kidney injury as:
- Assess for progression based on 1:
- Decline in GFR category with ≥25% drop in eGFR from baseline
- Rapid progression (sustained decline >5 mL/min/1.73 m²/year)
- Multiple serum creatinine measurements over time increase confidence in progression assessment
Step 3: Evaluate for Reversible Causes
- Medication review: identify nephrotoxic medications or those requiring dose adjustment 4
- ACE inhibitors/ARBs (may cause acute decline in renal function)
- NSAIDs
- Certain antibiotics
- Contrast agents
- Rule out pre-renal causes:
- Volume depletion
- Heart failure
- Liver disease
- Rule out post-renal causes:
- Urinary tract obstruction (consider renal ultrasound)
- Evaluate for exogenous factors affecting creatinine levels:
- Creatine supplements 5
- Dietary factors
- Muscle mass changes
Step 4: Laboratory Workup
- Complete blood count
- Comprehensive metabolic panel (including electrolytes, BUN, creatinine)
- Serum calcium, phosphorus, and PTH (if eGFR <60 mL/min/1.73 m²)
- Lipid profile
- Urinalysis with microscopy
- Urine protein electrophoresis (if suspecting paraproteinemia)
- Consider cystatin C-based eGFR for patients with abnormal muscle mass 6
- HbA1c (to assess for diabetes)
Step 5: Imaging and Additional Testing
- Renal ultrasound (to assess kidney size, echogenicity, and rule out obstruction)
- Consider further imaging based on clinical suspicion:
- CT scan (without contrast if eGFR <30 mL/min/1.73 m²)
- MRI (without gadolinium if eGFR <30 mL/min/1.73 m²)
- Consider kidney biopsy if:
- Rapid decline in renal function
- Nephrotic syndrome
- Unexplained hematuria and proteinuria
- Suspected glomerular disease
Step 6: Management Considerations
- Blood pressure control (target based on comorbidities) 1
- Glycemic control if diabetic 1
- Protein intake approximately 0.8 g/kg/day 1, 3
- Medication dose adjustments for renal function 4
- For ACE inhibitors: adjust dose based on creatinine clearance
- For eGFR ≥10 to ≤30 mL/min, initial dose of 5 mg for lisinopril
- For eGFR <10 mL/min, initial dose of 2.5 mg for lisinopril
Step 7: Referral to Nephrology
Consider referral to a nephrologist in the following situations 1:
- eGFR <30 mL/min/1.73 m² (CKD stage 4-5)
- Rapid progression (decline >5 mL/min/1.73 m²/year)
- UACR >300 mg/g
- Persistent hematuria
- Uncontrolled hypertension despite appropriate therapy
- Persistent electrolyte abnormalities
- Recurrent or extensive nephrolithiasis
- Hereditary kidney disease
Important Caveats
- Small fluctuations in GFR are common and do not necessarily indicate progression 1
- Patients with diabetes should have eGFR and UACR evaluated at least annually 1
- Patients with CKD have increased cardiovascular risk and mortality 3, 7
- Rapid eGFR decline (>4 mL/min/1.73 m²/year) is associated with worse outcomes including kidney failure, mortality, and cardiovascular events 2
- When initiating ACE inhibitors or ARBs, an initial decline in eGFR is expected and does not necessarily warrant discontinuation unless severe 4, 7