In a 78‑year‑old man with an estimated glomerular filtration rate (eGFR) of 88 mL/min/1.73 m², what is the appropriate evaluation and management of kidney stones, and are any renal dose adjustments needed for stone‑preventive medications?

EGFR and Kidney Stones: Evaluation and Management in a 78-Year-Old Man

Initial Assessment

In a 78-year-old man with an eGFR of 88 mL/min/1.73 m², kidney function is essentially normal for his age, and standard evaluation and management of kidney stones should proceed without renal dose adjustments for most stone-preventive medications. 1, 2

• Normal GFR is approximately 130 mL/min/1.73 m² for younger men, with a mean decline of 0.75 mL/min/year starting in the third or fourth decade. 1
• In adults older than 70 years, eGFR values between 60-90 mL/min/1.73 m² are often considered normal age-related changes rather than pathologic kidney disease. 2
• An eGFR of 88 mL/min/1.73 m² does not meet criteria for chronic kidney disease (CKD), which is defined as eGFR <60 mL/min/1.73 m² or albuminuria ≥30 mg/g creatinine. 1

Clinical Significance of Kidney Stones and Renal Function

Kidney stones may be associated with progressive decline in renal function, particularly in overweight patients, making appropriate stone management important for preserving kidney function. 3, 4

• Among overweight persons (BMI ≥27 kg/m²), stone formers have a mean eGFR that is 3.4 mL/min/1.73 m² lower than non-stone formers, and nearly twice the risk of having an eGFR between 30-59 mL/min/1.73 m². 3
• Stone removal by extracorporeal shock wave lithotripsy (ESWL) is associated with delayed CKD progression, with annual eGFR decline slowing from -1.63 mL/min/1.73 m²/year before ESWL to -0.29 mL/min/1.73 m²/year after successful stone removal. 4

Medication Dosing Considerations

No renal dose adjustments are required for stone-preventive medications at an eGFR of 88 mL/min/1.73 m². 5, 1

• Dose adjustments for renally excreted medications are generally not needed until eGFR falls below 60 mL/min/1.73 m². 1
• Standard dosing of thiazide diuretics, potassium citrate, and allopurinol can be used without modification at this level of kidney function. 5

Important Caveats for Elderly Patients

• In elderly patients with reduced muscle mass, serum creatinine may underestimate the degree of renal insufficiency, and calculated creatinine clearance using the Cockcroft-Gault formula may provide additional information for medication dosing decisions. 6, 7
• The Cockcroft-Gault formula is: CrCl (mL/min) = [(140 - age) × weight (kg)]/[72 × serum creatinine (mg/dL)] × (0.85 if female). 6
• For this 78-year-old patient, calculating actual creatinine clearance may be prudent if prescribing medications with narrow therapeutic indices. 7

Nephrotoxin Avoidance

Avoid nephrotoxic agents that could accelerate kidney function decline, particularly NSAIDs, which are commonly used for stone-related pain. 8, 6

• NSAIDs should be avoided or used with extreme caution, as they increase nephrotoxicity risk and can precipitate acute kidney injury in elderly patients. 8, 6
• If contrast imaging is required for stone evaluation, ensure adequate hydration and use the minimum necessary contrast volume. 8
• Review all current medications for potential nephrotoxins including ACE inhibitors and diuretics, which may require temporary adjustment during acute stone episodes. 6

Monitoring Recommendations

Regular monitoring of kidney function is essential in stone formers to detect early decline. 4

• Annual eGFR monitoring is appropriate for patients with kidney stones and normal baseline function. 4
• More frequent monitoring (every 3-6 months) should be considered if stones are recurrent, if the patient is overweight, or if stone removal procedures are performed. 6, 4