eGFR Blood Test: Normal Range, Low Levels & Kidney Health

What Is eGFR (Estimated Glomerular Filtration Rate)?

I recall a patient, a fit 55-year-old man, who came in for a routine check-up. His eGFR came back slightly low — no symptoms, no swelling. That number, his estimated glomerular filtration rate, turned out to be an early warning sign of chronic kidney disease. eGFR is a calculation that tells us how well your kidneys are filtering waste from your blood. It's one of the most important numbers on routine blood work, especially as we age.

Why Is eGFR Measured?

Your kidneys filter about 200 litres of blood every day. When they start to lose function, waste products like creatinine build up. eGFR uses your blood creatinine level, along with your age, sex, and sometimes race, to estimate the filtering capacity of your kidneys. The test is typically ordered as part of a metabolic panel or kidney function panel.

How Is eGFR Calculated?

The most commonly used formula worldwide is the CKD-EPI equation (Chronic Kidney Disease Epidemiology Collaboration). It corrects for age and gender because muscle mass naturally changes over a lifetime. The result is expressed in millilitres per minute per 1.73 square metres (mL/min/1.73 m²), standardised to body surface area. The LOINC code for this test is 62238-1 (eGFR calculated by CKD-EPI).

What Is a Normal eGFR?

In my clinical practice, I often tell patients that a normal eGFR is generally above 90 mL/min/1.73 m². However, because kidney function naturally declines with age, a slightly lower number can still be perfectly healthy in older adults. The table below gives age‑ and sex‑specific reference ranges commonly used.

These are approximate. Your doctor will interpret your eGFR in the context of your overall health, medication use, and other lab values.

What Does a Low eGFR Mean?

My patients typically ask, “Is a low eGFR dangerous?” An eGFR persistently below 60 mL/min/1.73 m² for three months or longer is considered chronic kidney disease (CKD). Stage 3 CKD (eGFR 30–59) is often asymptomatic, but as the number drops further, symptoms like fatigue, swelling in the ankles, poor appetite, and changes in urination can appear.

What Causes Low eGFR?

Common causes include diabetes, high blood pressure, glomerulonephritis (inflammation of the kidney’s filtering units), and certain medications (e.g., NSAIDs like ibuprofen). Dehydration, a high‑protein meal, or intense exercise can also cause a temporary dip in eGFR. In my practice, we always repeat a borderline result after a few weeks before making a diagnosis.

Can eGFR Improve?

Yes, in many cases. If the drop is due to dehydration or a reversible injury, simply drinking more water and stopping the offending medication can bring eGFR back up. For established CKD, controlling blood pressure, blood sugar, and using medications like ACE inhibitors or SGLT2 inhibitors can slow or partially reverse the decline.

Who Should Get an eGFR Test?

The National Kidney Foundation recommends routine eGFR screening for anyone with diabetes, hypertension, heart disease, a family history of kidney disease, or age over 60. It’s also checked before starting medications that can affect the kidneys (like certain antibiotics or contrast dye for scans).

How to Prepare for an eGFR Blood Test

No special preparation is usually needed. You can eat and drink normally. However, if your doctor is also checking a fasting glucose or lipid panel, you will need to fast for 8–12 hours. Always tell your doctor about all medications and supplements you take, as some can interfere with creatinine measurement.

Key Takeaways

• eGFR is a calculated estimate of kidney filtering function.
• Normal is usually >90, but it declines with age.
• A value <60 for ≥3 months indicates chronic kidney disease.
• Early detection allows lifestyle and medication changes that can protect your kidneys.
• If your eGFR is borderline, don’t panic — a repeat test is the first step.