Clinical Significance of Normal Creatinine with Elevated eGFR
An eGFR of 120 mL/min/1.73 m² with a creatinine of 36 µmol/L (approximately 0.41 mg/dL) represents normal kidney function, though the elevated eGFR may reflect hyperfiltration in certain clinical contexts, particularly early diabetes, or may simply indicate low muscle mass artificially lowering creatinine. 1, 2
Understanding the Discordance
Why This Pattern Occurs
Low muscle mass is the most common explanation for low creatinine with normal-to-high eGFR, as creatinine is generated from muscle catabolism and reduced muscle mass falsely lowers serum creatinine independent of actual kidney function 2
Elderly patients, those with sarcopenia, chronic illness, or malnutrition commonly demonstrate this pattern where serum creatinine does not reflect age-related GFR decline due to concomitant decline in muscle mass 2
Vegetarian diet reduces dietary creatine intake, lowering creatinine generation independent of kidney function 2
Normal variation exists, as normal GFR is approximately 130 mL/min/1.73 m² for men and 120 mL/min/1.73 m² for women, making this value within expected range 1
Special Clinical Context: Diabetes
Patients with diabetes often have elevated GFR in the early years after diagnosis, and this hyperfiltration can show histological evidence of diabetic kidney disease even when GFR appears normal or elevated 1
GFR less than 90 mL/min may represent significant loss of function in diabetic patients with early hyperfiltration, though your value of 120 mL/min/1.73 m² does not meet this threshold 1
Clinical Assessment Required
Evaluate for Underlying Conditions
Screen for diabetes if not already done, as elevated GFR can be an early marker of diabetic kidney disease with hyperfiltration 1
Assess muscle mass and nutritional status through history and physical examination, as skeletal muscle diseases, malnutrition, or sarcopenia dramatically reduce creatinine generation disproportionately to kidney function 2
Review dietary patterns, particularly vegetarian diet or creatine supplementation, which alter creatinine production without indicating renal dysfunction 2
Confirm Kidney Function Accuracy
Do not rely on a single estimated GFR calculation - the confirmatory test should not be the same as the screening test 3
Measure urine albumin-to-creatinine ratio (ACR) in a random urine specimen, as persistent proteinuria is the principal marker of kidney damage and would indicate CKD stage 1 (normal GFR with kidney damage) 3
Consider cystatin C-based eGFR if there is concern about creatinine reliability, as it is less biased by muscle mass, age, and race 2
Clinical Significance and Management
No Immediate Concern in Most Cases
This combination does not indicate kidney disease in the absence of proteinuria or other markers of kidney damage 3, 4
An eGFR greater than 60 mL/min/1.73 m² does not exclude kidney disease, but requires evidence of kidney damage (proteinuria, hematuria, structural abnormalities) to diagnose CKD 4
When to Pursue Further Evaluation
If diabetes is present: Screen annually for microalbuminuria and monitor for progression, as elevated GFR may represent early diabetic hyperfiltration 1
If proteinuria is detected: This would classify the patient as CKD stage 1 (GFR ≥90 mL/min/1.73 m² with kidney damage) requiring nephrology follow-up 3
If muscle wasting conditions exist: Consider 24-hour urine creatinine clearance or direct GFR measurement using clearance methods (iothalamate or iohexol) as the gold standard when creatinine-based estimates are unreliable 2
Monitoring Strategy
Repeat assessment in 3 months if there is clinical suspicion of kidney disease to determine if abnormalities persist, as CKD definition requires decreased GFR or kidney damage persisting for 3 or more months 3
No specific intervention is needed for isolated elevated eGFR with normal creatinine in the absence of diabetes, proteinuria, or other kidney damage markers 1, 3