What are the implications and management of an elevated eGFR?

Understanding an Elevated eGFR of 140 mL/min/1.73 m²

Clinical Significance

An eGFR of 140 mL/min/1.73 m² is above the normal range and represents hyperfiltration, which requires investigation for underlying causes rather than treatment of kidney dysfunction. Normal eGFR ranges from approximately 90-120 mL/min/1.73 m² in healthy adults, with values declining with age 1.

What Hyperfiltration Indicates

Population Context

• In younger adults (18-39 years), the median eGFR ranges from 128 at age 18 to approximately 110 by age 39, with values at the 90th percentile reaching even higher 2
• An eGFR of 140 would place this patient well above the median for their age group, indicating significant hyperfiltration 2

Common Underlying Causes to Investigate

Diabetes mellitus is the most important cause to rule out, as early diabetic kidney disease characteristically presents with glomerular hyperfiltration before any decline in function occurs 1. Check:

• Fasting glucose and HbA1c
• Urine albumin-to-creatinine ratio (UACR), as albuminuria may be present even with elevated eGFR 1

Pregnancy causes physiological hyperfiltration with eGFR increases of 40-50% above baseline 1.

High protein intake or recent high-protein meal can transiently elevate eGFR through increased renal blood flow 1.

Acute volume expansion from aggressive IV fluid administration increases glomerular filtration transiently 1.

Hyperthyroidism increases metabolic rate and renal blood flow, elevating eGFR 3.

Low muscle mass (sarcopenia) causes falsely elevated creatinine-based eGFR calculations because creatinine production is reduced 1. Consider:

• Measuring cystatin C-based eGFR for more accurate assessment 1
• Using the CKD-EPI cystatin C equation, which is valid even at eGFR >60 mL/min/1.73 m² 1

Essential Diagnostic Workup

Laboratory Assessment

• Repeat eGFR measurement in 1-2 weeks to confirm persistence, as single values may not reflect steady-state kidney function 1
• Urine albumin-to-creatinine ratio (UACR) to detect early kidney damage despite elevated filtration 1
• Serum cystatin C if low muscle mass is suspected, as this provides muscle-mass-independent GFR estimation 1
• Fasting glucose and HbA1c to screen for diabetes 1
• Thyroid function tests (TSH, free T4) if hyperthyroidism is suspected 3

Clinical History Focus

• Dietary protein intake patterns (high-protein diets, bodybuilding supplements) 1
• Recent IV fluid administration or volume status changes 1
• Symptoms of diabetes (polyuria, polydipsia, weight loss) 1
• Symptoms of hyperthyroidism (palpitations, weight loss, heat intolerance) 3
• Pregnancy status in women of childbearing age 1

Management Approach

If Diabetes is Identified

• Target HbA1c <7.0% for most patients, with individualized targets between 6.5-8.0% based on hypoglycemia risk and comorbidities 1
• Blood pressure control to <130/80 mmHg if albuminuria is present 1
• Initiate ACE inhibitor or ARB if UACR >30 mg/g (moderately increased albuminuria) 1
• Consider SGLT2 inhibitor for renoprotection if eGFR ≥20 mL/min/1.73 m² 1, 4
• Monitor UACR and eGFR at least annually, more frequently (twice yearly) if UACR >300 mg/g develops 1

If No Pathology is Found

• Reassure the patient that isolated hyperfiltration without albuminuria or other kidney damage markers does not require treatment 1
• Recheck eGFR and UACR annually to monitor for development of kidney disease 1
• Counsel on maintaining normal protein intake (0.8 g/kg/day) rather than excessive protein supplementation 1

Critical Pitfalls to Avoid

Do not assume elevated eGFR means "super-healthy kidneys" – hyperfiltration is often the earliest sign of diabetic kidney disease before any decline occurs 1.

Do not ignore the possibility of measurement error from low muscle mass, as creatinine-based equations systematically overestimate eGFR in sarcopenic patients 1. Always consider cystatin C-based estimation in elderly, malnourished, or low-muscle-mass individuals 1.

Do not overlook albuminuria screening – kidney damage can be present even with elevated eGFR, particularly in early diabetes 1.

Do not dismiss transient causes like recent high-protein meals, IV fluids, or acute illness, which can temporarily elevate eGFR without representing true hyperfiltration 1.