eGFR Blood Test Explained: What Your Kidney Number Really Means

You received your blood test results and spotted a value called eGFR — perhaps flagged low, perhaps just unfamiliar. eGFR stands for estimated Glomerular Filtration Rate, and it is the single most important number for assessing how well your kidneys are working. In the UK, the NHS routinely checks eGFR for everyone with diabetes, high blood pressure, or kidney disease risk — and millions of people receive this result every year without a clear explanation of what it means. In the US, the National Kidney Foundation estimates that 1 in 7 adults has chronic kidney disease (CKD), and most don't know it. This guide gives you a complete, jargon-free explanation of eGFR: what it measures, what your number means, the five stages of kidney disease, and exactly what to do next.

What is eGFR?

eGFR — estimated Glomerular Filtration Rate — is a calculated estimate of how much blood your kidneys filter per minute, adjusted for body surface area. Your kidneys contain around one million tiny filtering units called glomeruli. Each one filters waste products, excess fluid, and toxins from your blood into urine while keeping important proteins and blood cells in circulation. A healthy pair of kidneys filters approximately 90–120 millilitres of blood per minute. When the kidneys are damaged or diseased, this filtration rate drops — and eGFR is the number that tracks it.

• eGFR is calculated from your creatinine level, age, and sex — not measured directly
• It is reported in mL/min/1.73m² (millilitres per minute, standardised to average body surface area)
• A normal eGFR is 90 or above — values below 60 suggest chronic kidney disease if persistent
• eGFR naturally declines slightly with age — a 75-year-old with eGFR 65 may have perfectly normal kidneys for their age
• A single low eGFR is not necessarily alarming — the pattern over time matters far more than one reading

What is Creatinine and Why Does It Matter?

eGFR is calculated primarily from your blood creatinine level. Creatinine is a natural waste product produced at a constant rate by your muscles as they break down creatine phosphate for energy. Healthy kidneys continuously filter creatinine out of the blood into urine. When kidney function declines, creatinine accumulates in the blood — and a raised creatinine level is one of the earliest signals that something may be wrong.

• Normal creatinine range (men): 62–115 µmol/L (UK) / 0.7–1.3 mg/dL (US)
• Normal creatinine range (women): 44–97 µmol/L (UK) / 0.6–1.1 mg/dL (US)
• Creatinine rises as kidney function falls — the relationship is inverse
• Creatinine alone can be misleading — a muscular person naturally has higher creatinine without kidney disease
• eGFR corrects for this by factoring in age and sex — giving a more accurate picture than creatinine alone

eGFR Normal Range and the 5 Stages of Kidney Disease

Doctors use eGFR alongside urine tests to classify kidney health into six categories — G1 through G5. These are not strictly "disease stages" for everyone — G1 and G2 in the absence of other markers of kidney damage are considered normal. The table below gives you the full picture:

• G1 — eGFR 90 or above: Normal kidney function. Only concerning if kidney damage markers (protein in urine) are present.
• G2 — eGFR 60–89: Mildly reduced. Very common with age. Only concerning if combined with urine abnormalities or other damage markers.
• G3a — eGFR 45–59: Mildly to moderately reduced. Monitoring every 6–12 months recommended. Review medications.
• G3b — eGFR 30–44: Moderately to severely reduced. Referral to a kidney specialist (nephrologist) often recommended. Dietary review advised.
• G4 — eGFR 15–29: Severely reduced. Specialist care essential. Preparing for possible kidney replacement therapy discussed.
• G5 — eGFR below 15: Kidney failure. Dialysis or kidney transplant required.

What Causes Low eGFR?

Many conditions can reduce kidney function and lower eGFR. Some are reversible (acute causes), while others cause progressive, long-term damage (chronic causes). Identifying the cause is the essential first step in treatment.

• Diabetes mellitus: the leading cause of CKD in the UK and US — high blood sugar damages the glomeruli over years
• High blood pressure (hypertension): the second most common cause — sustained pressure damages kidney blood vessels
• Dehydration: causes temporary eGFR reduction — easily reversed with adequate fluid intake
• Glomerulonephritis: inflammation of the kidney filters — can be autoimmune (IgA nephropathy, lupus nephritis)
• Recurrent kidney infections (pyelonephritis): repeated infections can scar kidney tissue
• Polycystic kidney disease (PKD): inherited condition causing fluid-filled cysts to replace kidney tissue
• NSAIDs (ibuprofen, naproxen): long-term or high-dose use reduces blood flow to kidneys
• Certain antibiotics and contrast dyes: used in CT scans can cause acute kidney injury
• Obstruction: kidney stones, enlarged prostate, or tumours blocking urine flow
• Ageing: eGFR naturally declines approximately 1 mL/min/year after age 40

uACR — The Other Kidney Test You Need to Know

eGFR tells you how well your kidneys are filtering. uACR (Urine Albumin-to-Creatinine Ratio) tells you whether your kidneys are leaking protein — a key early sign of damage that can be present even when eGFR is still normal. Together, eGFR and uACR give the full picture of kidney health. The NHS and American Diabetes Association recommend both tests for anyone at risk of CKD.

• Normal uACR: below 3 mg/mmol (UK) / below 30 mg/g (US) — no significant protein leakage
• Mildly increased (A2): 3–30 mg/mmol — early kidney damage, especially in diabetes and hypertension
• Severely increased (A3): above 30 mg/mmol — significant kidney damage, requires specialist review
• Protein in urine (proteinuria) can be detected years before eGFR starts to fall — early detection enables early treatment
• The uACR is a simple urine test, usually done at the same time as a blood test for eGFR

Symptoms of Low eGFR and Kidney Disease

One of the most dangerous aspects of chronic kidney disease is that it is largely symptom-free until function is severely reduced. Most people with eGFR between 30 and 60 feel completely well. Symptoms, when they do appear, often include:

• Swollen ankles, feet, or hands (fluid retention due to poor kidney filtration)
• Fatigue and weakness — kidneys produce erythropoietin; CKD causes anaemia
• Foamy or bubbly urine — protein leaking into urine creates foam
• Blood in urine (haematuria) — may appear pink, red, or cola-coloured
• More frequent urination, particularly at night (nocturia)
• High blood pressure — kidneys regulate blood pressure; damage causes hypertension
• Nausea and loss of appetite — waste products accumulating in the blood
• Itchy skin — uraemia (waste in the blood) causes skin irritation
• Muscle cramps — electrolyte imbalances due to poor kidney regulation

What to Do if Your eGFR is Low

A single low eGFR result is a prompt to investigate further — not to panic. Here is a practical, step-by-step guide:

• Step 1 — Recheck: A low eGFR on one test is not a diagnosis. Ensure you were well-hydrated and had not eaten high-protein food before the test. Repeat the test in 2–4 weeks.
• Step 2 — Get a uACR: Request a urine albumin test at the same appointment. This is essential to assess kidney damage alongside eGFR.
• Step 3 — Review medications: NSAIDs (ibuprofen), certain blood pressure drugs, and contrast agents can temporarily worsen eGFR. Discuss with your doctor.
• Step 4 — Control blood pressure: Target below 130/80 mmHg, or below 125/75 if significant proteinuria is present. Blood pressure control is the most powerful tool to slow CKD progression.
• Step 5 — Control blood sugar: If diabetic, keep HbA1c below 53 mmol/mol (7%). SGLT2 inhibitors (e.g. empagliflozin) have strong evidence for kidney protection.
• Step 6 — Dietary adjustments: Reduce salt, limit NSAIDs, stay well hydrated, and moderate protein intake if advised by your nephrologist.
• Step 7 — Specialist referral: If eGFR is below 30, or falling rapidly (>5 mL/min/year), or accompanied by heavy proteinuria — ask for a nephrology referral.

Who Should Get an eGFR Test?

The NHS recommends routine eGFR testing for the following groups. If you fall into any of these categories and have not had a recent kidney function test, speak to your GP:

• Type 1 or Type 2 diabetes — annually from diagnosis
• High blood pressure (hypertension) — annually
• Cardiovascular disease (heart disease, stroke, peripheral artery disease)
• First-degree relative with kidney disease or inherited kidney condition
• Recurrent kidney infections or kidney stones
• Long-term use of NSAIDs (ibuprofen, naproxen, diclofenac)
• Systemic lupus erythematosus (SLE) or other autoimmune conditions
• Over 65 years of age — routine annual check recommended
• Obesity (BMI above 30)
• Black, Asian, or minority ethnic background — higher risk of diabetes-related CKD

Interpret Your Kidney Results with LabSense AI

Received your eGFR, creatinine, or uACR results and want to understand what they mean for your health? LabSense AI analyses your kidney function results alongside your other blood values and provides an instant, plain-English explanation — including whether your results are within the normal range and what the pattern suggests. Free, no sign-up, trusted by patients across the UK, US, and 50+ countries. Enter your results and get clarity in under 60 seconds.