What are the next best steps for a 90-year-old male with impaired renal function (eGFR 90, creatinine (Cr) 1.30)?

Management of a 90-Year-Old Male with eGFR 90, Cr 1.30

Despite a normal eGFR of 90 mL/min/1.73m², this 90-year-old male requires comprehensive renal function evaluation and monitoring due to his age and elevated creatinine level.

Initial Assessment

The patient presents with:

• Normal eGFR (90 mL/min/1.73m²)
• Elevated creatinine (1.30 mg/dL)

This represents a discordance between eGFR and creatinine that warrants further investigation. According to the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure, a serum creatinine >1.3 mg/dL in men may indicate chronic kidney disease (CKD), even with a normal eGFR 1.

Recommended Next Steps

1. Verify renal function with additional testing:

   • Obtain urinary albumin-to-creatinine ratio (UACR) to assess for albuminuria 1
   • Consider cystatin C measurement for more accurate GFR assessment 2
   • Calculate eGFR using both Cockcroft-Gault and MDRD equations to compare results 1

2. Evaluate for potential causes of elevated creatinine:

   • Review medication list for nephrotoxic drugs (NSAIDs, certain antibiotics)
   • Check for dietary supplements containing creatine that may artificially elevate creatinine 3
   • Assess hydration status and recent dietary intake

3. Screen for comorbidities that affect kidney function:

   • Check blood pressure (target <130/80 mmHg) 4
   • Test for diabetes (HbA1c, fasting glucose)
   • Evaluate cardiovascular status (lipid panel, cardiac assessment)

4. Laboratory workup:

   • Complete metabolic panel (electrolytes, BUN)
   • Complete blood count
   • Urinalysis with microscopy
   • Consider renal ultrasound to assess kidney structure

Interpretation and Management

If albuminuria is present (UACR ≥30 mg/g):

• Initiate ACE inhibitor or ARB at low dose with careful monitoring 4
• Monitor serum potassium and creatinine within 7-14 days after initiation 4

If no albuminuria but elevated creatinine persists:

• Consider more accurate GFR measurement methods such as 51Cr-EDTA or inulin clearance 1, 5
• Regular monitoring of renal function every 3-6 months 4

For all patients:

• Implement renoprotective strategies:
  • Avoid nephrotoxic medications (NSAIDs, certain antibiotics) 1, 4
  • Ensure adequate hydration
  • Optimize blood pressure control
  • Dietary protein intake of approximately 0.8 g/kg body weight per day 1, 4
  • Sodium restriction to <2.0 g/day 4

Important Considerations

1. Age-related kidney changes: Renal function typically declines by 1% per year after age 30-40, so a 90-year-old would be expected to have reduced GFR 1. The normal eGFR of 90 mL/min/1.73m² in this patient is unusual and may reflect inaccurate estimation.

2. Limitations of eGFR equations: The MDRD equation has not been well-validated in persons older than 70 years 1. In elderly patients, creatinine-based eGFR may overestimate actual GFR due to decreased muscle mass 1, 6.

3. Discordance between markers: When there are large discordances between creatinine and cystatin C-based estimations, using both markers together (eGFRcr-cys) provides more accurate assessment 2.

4. Cancer considerations: If this patient has or is being evaluated for cancer, more precise GFR measurement may be needed, as chemotherapeutic agents often require dose adjustments based on renal function 6, 5.

Regular monitoring of renal function is essential in this elderly patient, even with a currently normal eGFR, as age-related decline in kidney function is expected and may impact medication dosing and overall health outcomes.