Why GFR of 60 Appears Normal on CMP
A GFR of 60 mL/min/1.73 m² is not reported as a specific numeric value by clinical laboratories because estimating equations have reduced accuracy at higher GFR levels, and laboratories are instructed to report values ≥60 mL/min/1.73 m² simply as ">60" rather than providing a precise number. 1
Laboratory Reporting Standards
Clinical laboratories automatically report eGFR values above 60 mL/min/1.73 m² as ">60 mL/min/1.73 m²" rather than as precise figures because the accuracy of eGFR calculations is suboptimal in patients with normal or near-normal renal function. 2
The MDRD and CKD-EPI equations show reduced precision when GFR exceeds 60 mL/min/1.73 m², with significant overlap between healthy individuals and those with early kidney disease. 1, 3
This reporting convention means that a patient with an actual GFR of 60,75, or even 90 mL/min/1.73 m² would all receive the same laboratory report of ">60," making them appear "normal" on the CMP. 2
The 60 mL/min/1.73 m² Threshold
The cutoff of 60 mL/min/1.73 m² represents less than half of the normal GFR in young adults (approximately 125 mL/min/1.73 m² in men and 120 mL/min/1.73 m² in women), and this threshold was chosen because it correlates with increased risk for CKD complications, cardiovascular disease, and mortality. 1
CKD is only diagnosed when GFR remains <60 mL/min/1.73 m² for ≥3 months or when markers of kidney damage (albuminuria ≥30 mg/g, structural abnormalities, or pathological changes) are present, regardless of GFR level. 1
A GFR of exactly 60 mL/min/1.73 m² sits at the diagnostic threshold for CKD Stage 3a (GFR 45-59 mL/min/1.73 m²), but interpretation requires clinical context including presence of proteinuria, rate of decline, and patient age. 1
Age-Related Considerations
GFR physiologically declines with age at approximately 0.75 mL/min/year, and values around 60 mL/min/1.73 m² may be considered normal in adults over 70 years old, though this remains controversial in guideline definitions. 1, 4
The fixed cutoff of 60 mL/min/1.73 m² does not adequately account for age-related physiological decline, leading to potential overdiagnosis of CKD in elderly patients without true kidney disease. 4
Common Pitfalls
Serum creatinine alone grossly overestimates kidney function and can remain seemingly normal (e.g., 1.3 mg/dL) despite significantly reduced GFR, which is why eGFR reporting was implemented. 1
The reference interval for serum creatinine includes up to 25% of people (particularly thin, elderly women) who actually have eGFR <60 mL/min/1.73 m², making creatinine an unreliable standalone marker. 2
eGFR accuracy is compromised in extremes of muscle mass, obesity, amputees, non-steady-state conditions (acute illness), and immediately post-surgery, requiring clinical judgment rather than relying solely on the calculated value. 1, 5
Clinical Implications
A single eGFR value of 60 mL/min/1.73 m² without albuminuria or other markers of kidney damage does not definitively indicate CKD and requires repeat testing after 3 months to confirm chronicity. 1
Nephrology referral should be considered when eGFR falls below 45 mL/min/1.73 m² (CKD Stage 3b) or when progressive decline occurs, especially if accompanied by proteinuria. 1, 6
The imprecision of eGFR equations means that approximately 80-84% of calculated values fall within 30% of measured GFR, creating substantial uncertainty around borderline values like 60 mL/min/1.73 m². 7