A normal estimated glomerular filtration rate (eGFR) is generally 90 mL/min/1.73 m² or higher. Readings of 60–89 mL/min/1.73 m² suggest mildly reduced kidney function and can be normal with aging; values below 60 indicate possible chronic kidney disease if persistent for three months or more. Interpretation depends on age, sex, muscle mass and overall clinical context; abnormal results warrant follow-up.

The cystatin C test measures a small protein made by all nucleated cells and cleared by the kidneys; its level reflects filtration. Used alone or combined with creatinine to calculate estimated glomerular filtration rate (eGFR), it helps assess kidney function more accurately—especially in older adults, people with abnormal muscle mass, or when creatinine-based estimates may be unreliable.

eGFR estimated from cystatin C is interpreted like creatinine-based eGFR: ≥90 mL/min/1.73 m² is considered normal; 60–89 mL/min/1.73 m² indicates mildly reduced function; <60 mL/min/1.73 m² suggests chronic kidney disease if persistent for over three months. Reference ranges vary by laboratory and decline with age; abnormal results require clinical correlation and repeat testing.

A low eGFR indicates reduced kidney filtering function. It can reflect acute problems (dehydration, medication effects) or chronic kidney disease from diabetes, high blood pressure, or other disorders. Lower eGFR raises risk of toxin buildup, fluid imbalance and altered medication dosing. Clinicians usually repeat tests, check urine and blood markers, adjust treatments, and may recommend lifestyle changes or specialist referral.

A good estimated GFR (eGFR) depends on age: ≥90 mL/min/1.73 m² is normal for young adults. After about age 40 eGFR normally falls ~1 mL/min/year; values 60–89 may be expected in older adults if there’s no kidney damage. An eGFR <60 for three months suggests chronic kidney disease. Discuss your specific result with a clinician — eGFR varies with age, sex and muscle mass.

Adequate hydration can improve or restore GFR when it’s reduced by dehydration by increasing renal blood flow and filtration. Rehydration may raise measured eGFR or creatinine clearance, but it won’t reverse chronic structural kidney damage. People with advanced CKD, heart failure, or fluid restrictions should consult their clinician before increasing fluid intake.