eGFR Calculator UK | Kidney Function Calculator 2025

Understanding eGFR and Kidney Function: A Complete UK Guide

Your kidneys are remarkable organs that filter approximately 180 litres of blood every day, removing waste products and excess fluid to produce around 1.5 litres of urine. The estimated Glomerular Filtration Rate (eGFR) is the best overall measure of how well your kidneys are performing this vital function. This comprehensive guide explains what eGFR means, how it's calculated, and what your results indicate about your kidney health.

What is eGFR?

eGFR stands for estimated Glomerular Filtration Rate. The glomeruli are tiny filtering units within your kidneys—each kidney contains approximately one million of these structures. The filtration rate measures how much blood passes through these filters per minute. A healthy young adult typically has an eGFR of around 100-120 mL/min/1.73m².

The "estimated" part is important because measuring actual GFR directly is complex and impractical. Instead, eGFR is calculated from a simple blood test measuring creatinine (a waste product from muscle metabolism), combined with age, sex, and sometimes ethnicity. This calculation provides a reliable estimate of kidney function for most people.

The CKD-EPI Equation Explained

This calculator uses the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation, developed in 2009 and recommended by both UK NICE (National Institute for Health and Care Excellence) and the NHS. The CKD-EPI equation is more accurate than the older MDRD formula, particularly at higher eGFR levels (above 60 mL/min/1.73m²).

The equation considers several factors: serum creatinine level (the primary input), age (kidney function naturally declines with age), sex (men typically have higher creatinine due to greater muscle mass), and historically, ethnicity. However, the use of ethnicity adjustment is increasingly debated in medical practice, with many UK laboratories now reporting eGFR without this adjustment.

Understanding CKD Stages

Chronic Kidney Disease (CKD) is classified into five stages based on eGFR. Understanding these stages helps patients and healthcare providers plan appropriate monitoring and treatment.

Importantly, CKD stages G1 and G2 require additional evidence of kidney damage (such as protein in urine or structural abnormalities) to be classified as CKD. An eGFR of 60-89 alone without other markers is often normal, particularly in older adults.

CKD in the UK: Statistics and Impact

Chronic kidney disease affects approximately 3 million people in the UK, making it a significant public health concern. According to NHS Digital data, around 10% of the adult UK population has some degree of CKD, though most cases are mild (stages G1-G2) and may never progress to requiring treatment.

The NHS spends over £1.5 billion annually treating CKD and its complications. End-stage renal disease (stage G5) requiring dialysis or transplant affects around 60,000 UK patients. Early detection through eGFR testing can help prevent progression and reduce the need for expensive treatments.

Common Causes of Reduced eGFR

Several conditions can lead to reduced kidney function. Understanding these causes helps with prevention and early intervention:

• Diabetes: The leading cause of CKD in the UK. High blood sugar damages the kidney's filtering units over time. Diabetic kidney disease accounts for approximately 25% of all CKD cases.
• High blood pressure (hypertension): Causes damage to the small blood vessels in the kidneys. Uncontrolled hypertension is responsible for about 10% of CKD cases.
• Glomerulonephritis: Inflammation of the glomeruli, often caused by immune system disorders. This condition can be acute or chronic.
• Polycystic kidney disease: An inherited condition causing cysts to develop in the kidneys. Affects approximately 1 in 1,000 people in the UK.
• Recurrent kidney infections: Repeated urinary tract infections that reach the kidneys can cause scarring and permanent damage.
• Obstruction: Kidney stones, enlarged prostate, or other blockages can impair kidney function if untreated.
• Medications: Long-term use of certain drugs, particularly NSAIDs (like ibuprofen) and some antibiotics, can affect kidney function.

Age and eGFR: What's Normal?

Kidney function naturally declines with age, even in healthy individuals. After age 30, eGFR typically decreases by approximately 1 mL/min/1.73m² per year. This means a healthy 70-year-old might have an eGFR of 70-80 mL/min/1.73m², which would be concerning in a 30-year-old but may be normal for their age.

UK NICE guidelines recognise this age-related decline. For people over 70, an eGFR of 45-59 (stage G3a) may be stable and not represent significant kidney disease, particularly if there's no protein in the urine and no other risk factors. However, regular monitoring is still recommended.

What to Do If Your eGFR is Low

If this calculator suggests your eGFR may be reduced, here are the recommended steps:

eGFR 60-89 (Stage G2)

Often normal, especially in older adults. Maintain a healthy lifestyle, stay well-hydrated, control blood pressure, and mention it at your next GP appointment. No urgent action typically needed unless you have other risk factors.

eGFR 45-59 (Stage G3a)

Schedule a GP appointment within the next few weeks. Your doctor will likely repeat the blood test and check for protein in your urine (albumin-to-creatinine ratio). They may review your medications and discuss lifestyle modifications.

eGFR 30-44 (Stage G3b)

Contact your GP promptly. You may be referred to a nephrologist (kidney specialist). More frequent monitoring will be needed, and dietary modifications may be recommended. Medication review is important to avoid drugs that can worsen kidney function.

eGFR Below 30 (Stages G4-G5)

Seek medical attention urgently. Specialist nephrology care is essential at this stage. Preparation for possible renal replacement therapy (dialysis or transplant) may begin. Close monitoring of electrolytes, anaemia, and bone health becomes crucial.

Protecting Your Kidneys: Evidence-Based Advice

Whether your kidney function is normal or reduced, these NHS-recommended strategies help protect and preserve kidney health:

• Control blood pressure: Target below 140/90 mmHg for most people, or below 130/80 if you have diabetes or CKD with significant proteinuria.
• Manage blood sugar: If diabetic, work with your healthcare team to achieve good glycaemic control (HbA1c below 48 mmol/mol for most people).
• Stay hydrated: Drink 1.5-2 litres of water daily unless advised otherwise. Dehydration makes kidneys work harder.
• Limit salt intake: Target less than 6g per day. Excess salt raises blood pressure and increases kidney workload.
• Eat a balanced diet: Include plenty of fruits, vegetables, and whole grains. Limit processed foods high in sodium and phosphorus.
• Maintain healthy weight: Obesity increases risk of diabetes and hypertension, both major CKD risk factors.
• Exercise regularly: NHS recommends 150 minutes of moderate activity weekly. Exercise helps control blood pressure and weight.
• Don't smoke: Smoking damages blood vessels including those in the kidneys. Quitting reduces CKD progression risk.
• Limit alcohol: Excessive alcohol can raise blood pressure and contribute to dehydration.
• Use medications carefully: Avoid overusing NSAIDs (ibuprofen, naproxen) and always take prescribed medications as directed.

Understanding Your Blood Test Results

When your GP orders kidney function tests, several markers are typically included. Understanding these helps you have informed conversations with your healthcare provider:

• Serum Creatinine: A waste product from muscle metabolism. Higher levels suggest reduced kidney function. Normal range is approximately 45-90 µmol/L for women and 60-110 µmol/L for men.
• Blood Urea Nitrogen (BUN): Another waste product filtered by kidneys. Normal range is 2.5-7.8 mmol/L. Elevated levels can indicate kidney problems but also dehydration or high protein intake.
• eGFR: Calculated from creatinine, age, and sex. Above 90 is generally normal; below 60 sustained over 3 months indicates CKD.
• Albumin-to-Creatinine Ratio (ACR): Measures protein leak in urine. Normal is below 3 mg/mmol. Elevated ACR indicates kidney damage even if eGFR is normal.

Limitations of eGFR

While eGFR is a valuable screening tool, it has limitations that healthcare providers consider:

• Extreme muscle mass: Very muscular individuals may have higher creatinine (lowering eGFR) without kidney disease. Conversely, muscle wasting can artificially raise eGFR.
• Diet effects: Recent high protein intake can temporarily raise creatinine. Some recommend avoiding excessive meat before blood tests.
• Acute changes: eGFR is designed for stable kidney function. During acute illness, creatinine changes may not accurately reflect true kidney function.
• Certain medications: Some drugs (like trimethoprim) can raise creatinine without affecting actual kidney function.
• Pregnancy: Normal pregnancy increases kidney filtration, so standard eGFR equations don't apply.

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