Kidney function blood tests (eGFR)
A blood test that measures creatinine and other markers to estimate how well your kidneys are filtering your blood, reported as an eGFR.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- eGFR estimates how well your kidneys filter, calculated from creatinine, age and sex; higher is better.
- It is an estimate, not an exact figure, and several non-kidney factors (muscle, diet, illness, medicines) can affect it.
- A single low or borderline result usually needs repeating; chronic kidney disease is diagnosed from results over time, not one test.
- Ask what your result means in your context, whether it needs repeating, and whether a urine test is also needed.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your specialist will give you advice for your situation.
Gives a simple, repeatable measure of kidney filtering that can be tracked over time
Relying on a single eGFR to diagnose chronic kidney disease without repeating it or looking at the trend.
A few minutes; you can continue your day straight away. Mild bruising is common.
Being given your actual result and a clear explanation of what it means for you.
A few minutes; you can continue your day straight away. Mild bruising is common.
The result is usually available. Your clinician interprets it alongside your history, medicines and any previous...
It is often repeated after a period, and a urine test may be added, to see whether the change is real and lasting.
If results stay reduced, chronic kidney disease may be diagnosed and a monitoring and management plan put in place.
What is a kidney function blood test (eGFR)?
A kidney function blood test measures substances in your blood that the kidneys normally control. The key one is creatinine, a waste product made by muscles and removed by the kidneys. From your creatinine, age and sex, a laboratory calculates an estimated glomerular filtration rate, or eGFR — a number that estimates how many millilitres of blood your kidneys filter each minute. The test usually comes as part of a 'U&E' panel, which also checks urea and salts such as sodium and potassium.
The higher the eGFR, the better the filtering. A result of 90 or above is generally normal, and values down to 60 can still be normal if there is no other sign of kidney disease. Lower results, especially if they persist, may point to chronic kidney disease (CKD), which is graded in stages.
It is important to understand that eGFR is an estimate, not an exact measurement. It can be thrown off by things that have nothing to do with kidney disease — for example a lot of muscle, very low muscle, a recent large meat meal, certain medicines, pregnancy, or a sudden illness. A single result is interpreted with caution, and one slightly low value does not by itself mean kidney disease.
This guide explains what the test shows and what it cannot tell you. It is not a diagnosis.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
What the eGFR ranges broadly mean
| eGFR (mL/min/1.73m²) | Broad meaning |
|---|---|
| 90 or above | Normal filtering (kidney disease only if other signs present) |
| 60–89 | Mildly reduced; often normal if no other signs |
| 30–59 | Moderately reduced (CKD stage 3) |
| 15–29 | Severely reduced (CKD stage 4) |
| Below 15 | Kidney failure (CKD stage 5) |
CKD is diagnosed from a reduced eGFR and/or signs such as protein in the urine present for at least three months, not from a single result.
Preparing for your test
- Ask whether you need to do anything special; for routine eGFR you usually do not need to fast.
- Some guidance suggests avoiding a large meat meal (and possibly fish) for about 12 hours before the test, as it can temporarily raise creatinine.
- Bring a list of your medicines and supplements; some, including certain antibiotics and creatine supplements, affect the result.
- Mention if you do heavy weight training or have a lot of, or very little, muscle, as this affects creatinine.
- Tell the team if you have been unwell, dehydrated, or have recently had contrast dye for a scan.
- If you might be pregnant, say so, as eGFR is interpreted differently in pregnancy.
- Bring any previous results so changes over time can be seen.
What happens
A small sample of blood is taken from a vein in your arm, usually at a GP surgery, clinic or hospital. It takes only a few minutes. There is no special recovery and you can carry on with your day.
The laboratory measures creatinine (and usually urea and salts) and calculates your eGFR. Your clinician then looks at the result alongside your age, your previous results, any urine test, your medicines and how you have been feeling. A single result is rarely acted on in isolation; a low or borderline value is often repeated, and CKD is only diagnosed when changes persist over months.
Is this test right for me?
A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.
May not be suitable if…
- Relying on a single eGFR to diagnose chronic kidney disease without repeating it or looking at the trend.
- Using eGFR alone to exclude kidney disease, when a urine test may be needed.
- Interpreting eGFR at face value in people with very high or very low muscle mass without caution.
- Using eGFR to judge kidney function during a rapidly changing acute illness, when it is unreliable.
Delay or rearrange if…
- You are acutely unwell, dehydrated or have recently had vomiting or diarrhoea, which can distort the result.
- You have recently had contrast dye for a scan, which can temporarily affect kidney function.
- You have just done very heavy exercise or eaten a large meat meal before a creatinine test.
- You are unsure which of your medicines or supplements might affect the result, until this is checked.
Alternatives to discuss
- A cystatin C-based eGFR to confirm or refine the result when creatinine may mislead.
- Urine albumin-to-creatinine ratio (ACR) to detect kidney damage that eGFR may miss.
- A formal measured GFR (a more involved test) in selected situations where precision matters.
- Repeating the test over time rather than acting on a single value.
Before you decide
Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Benefits
- Gives a simple, repeatable measure of kidney filtering that can be tracked over time
- Can pick up reduced kidney function before you have any symptoms
- Helps detect and stage chronic kidney disease so it can be managed early
- Guides safe dosing of many medicines that depend on kidney function
- Helps decide whether further tests, such as a urine test or scan, are needed
- Provides reassurance when results are stable and normal
Risks & complications
- Bruising or soreness where the blood is taken
- A borderline or mildly low result that causes worry but turns out to be normal for you
- Needing the test repeated to confirm a result
- A result affected by something temporary, such as a recent meal, dehydration or illness
- Over-diagnosis of 'kidney disease' from a single low reading without follow-up
- A misleading result in people with very high or very low muscle mass
- Being labelled with a stage of CKD before the result is confirmed over time
- False reassurance from a normal eGFR when kidney damage is shown only by urine tests
- Fainting during the blood test
The blood test itself is very low-risk; the main pitfalls are in interpretation. eGFR is an estimate and can be affected by muscle mass, diet, pregnancy, certain medicines and acute illness, so a single odd result should not be over-read. Equally, a normal eGFR does not rule out all kidney disease, because some problems show up only as protein or blood in the urine. Ask whether your result needs repeating and whether you also need a urine test.
Published figures to discuss
The blood test carries negligible physical risk, so meaningful 'rates' here concern interpretation rather than complications. eGFR is an estimate: it can be falsely low or high because of muscle mass, diet, pregnancy, certain medicines and acute illness, and a normal value does not exclude kidney damage shown only on urine testing. Because these effects vary from person to person, single reliable percentages for 'false results' are not meaningful, so the issues are described qualitatively.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| eGFR misread as exact kidney function | Common interpretation issue | eGFR is an estimate affected by age, muscle mass, pregnancy, acute illness and some medicines. | Guide sourcesClinical context |
| Acute kidney injury mistaken for chronic kidney disease | Avoidable with repeat/trend review | CKD requires abnormal kidney function or structure for more than 3 months unless there is clear prior evidence. | UK Kidney Association — Measurement of kidney function (eGFR)ukkidney.orgSource-linked context |
| Albuminuria not checked | Common gap | NICE CKD guidance uses urine ACR with eGFR to classify risk and guide treatment. | NICE — Chronic kidney disease (NG203)nice.org.ukSource-linked context |
| Urgent result missed | Safety-critical | Severe potassium abnormality, rapidly rising creatinine or very low eGFR may need same-day action. | Guide sourcesClinical context |
These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.
What happens afterwards
There is no physical recovery from a blood test. What matters afterwards is understanding what your result means in your situation and whether it needs repeating or further tests.
- Mild bruising where blood was taken
- Being asked to repeat the test to confirm a borderline result
- Being asked for a urine sample as well as blood
- No change to how you feel, as kidney problems are often silent
- Reassurance and a recheck date if the result is stable
Aftercare
- Make sure you know your result and what it means for you, not just whether it is 'normal'.
- Ask whether the result needs repeating and whether you should also have a urine test.
- Keep a record of your eGFR over time, as the trend matters more than a single value.
- Review medicines with a clinician or pharmacist if your kidney function is reduced.
- Stay well hydrated in line with any advice, and look after blood pressure and diabetes if relevant.
- Ask whether any of your medicines should be paused during illness with vomiting or diarrhoea ('sick-day rules').
- Attend any recommended follow-up so changes are not missed.
- Your actual eGFR result, not just 'normal' or 'abnormal'
- Any previous results, to see the trend
- A note of whether to avoid a large meat meal before a repeat test
- An up-to-date list of medicines and supplements
- Clarity on whether a urine (ACR) test is also needed
- A recheck date if you are being monitored
- Advice on 'sick-day' medicine rules if your kidney function is reduced
⚠ Get urgent help if…
- Passing much less urine than usual, or none at all
- Visible blood in the urine
- Swelling of the ankles, face or around the eyes
- Severe tiredness, breathlessness, nausea or confusion
- Vomiting or diarrhoea that stops you keeping fluids down, especially if you take kidney-related medicines
- Severe pain in the side or back
Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.
General guidance — it doesn't replace the specific advice your specialist gives you.
Results & realistic expectations
A normal eGFR (broadly 90 or above, and often down to 60 without other signs) suggests the kidneys are filtering well. A reduced result may indicate chronic kidney disease, but a single value is not enough to say so, because eGFR is an estimate and can be affected by temporary factors. CKD is diagnosed when a reduced eGFR and/or other signs persist over at least three months.
Just as importantly, a normal eGFR does not rule out every kidney problem. Some conditions show up mainly as protein or blood in the urine while filtering still looks normal, which is why a urine test often goes alongside the blood test. The most useful information comes from the trend over time and from blood and urine results read together.
A kidney function result reflects a moment in time and can change with illness, hydration, medicines and the natural, gradual fall in eGFR with age. If your result is normal, how often it is repeated depends on your risk factors. If you have reduced function or risk factors such as diabetes or high blood pressure, regular monitoring is used to track the trend. Your clinician will advise how often you should be retested.
Related tests, treatments or support
Kidney function blood tests are usually done as part of a U&E panel and are most useful alongside a urine albumin-to-creatinine ratio (ACR), blood pressure and, where relevant, blood sugar (HbA1c). If results suggest a problem, a kidney ultrasound and sometimes a kidney biopsy may follow to find the cause.
Follow-up & long-term care
Follow-up depends on the result and your risk. A one-off mildly reduced value in a well person may just be repeated; a confirmed reduction leads to a monitoring plan, attention to blood pressure and medicines, and sometimes referral to a kidney specialist. Make sure you know your result, when it will be rechecked, and who to contact with questions.
- Repeat eGFR at the interval your clinician advises, especially if you have diabetes or high blood pressure
- Periodic urine ACR testing alongside blood tests
- Blood pressure control, which protects kidney function
- Medication review and dose adjustment as kidney function changes
- Knowing 'sick-day rules' for pausing certain medicines during acute illness
Repeat, follow-on and what comes next
- A low or borderline result is commonly repeated before any diagnosis is made.
- Results are tracked over time, as the trend matters more than one value.
- A urine test is often added to complete the picture.
- A confirmed reduction leads to a monitoring plan and sometimes specialist referral, not a one-off label.
Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.
What good aftercare looks like
- Being given your actual result and a clear explanation of what it means for you.
- A sensible plan for repeating borderline results and adding a urine test if needed.
- Tracking of your eGFR trend over time rather than reacting to one value.
- Medication review and 'sick-day' advice if your kidney function is reduced.
- A clear recheck interval and referral route if results are abnormal.
What affects the cost
Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:
- Whether the test is a single eGFR or a fuller panel (U&E, with urine tests)
- Whether a urine albumin-to-creatinine ratio is included
- Whether a clinician consultation to interpret the results is part of the package
- How quickly results are reported
- Whether repeat or monitoring tests over time are included
- Any add-on tests, such as cystatin C, in selected cases
- Exactly which blood (and urine) tests are included
- Whether a clinician interprets the result and explains it to you
- Whether repeat or monitoring tests are covered
- How and when you receive your results, including the actual numbers
- What happens, and what it costs, if a result is abnormal and needs follow-up
- Whether referral or further tests (scan, specialist) are included if needed
- What happens if you need to move into NHS care
On the NHS? Kidney function tests are routine on the NHS and widely available privately; the result is most useful when interpreted in context and tracked over time rather than from a single value.
You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.
Consent traps and marketing red flags
These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.
Consent traps
- Being given a CKD 'stage' from a single test without it being confirmed over time.
- Not being told that eGFR is an estimate with important limitations.
- A normal result presented as a complete kidney all-clear without a urine test.
- No plan for what an abnormal result means or how it will be followed up.
- Not receiving your actual numbers, only a vague 'normal' or 'abnormal'.
Marketing red flags
- Selling a single eGFR as a definitive 'kidney health check'.
- Implying a normal eGFR rules out all kidney disease.
- Diagnosing or staging kidney disease from one blood test without follow-up.
- Not offering or mentioning a urine test where it would be appropriate.
- Promoting supplements or 'detox' products alongside the test.
Choosing a specialist safely
- Check the specialist is on the GMC Specialist Register for this area.
- Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
- You're entitled to time to consider and to have your questions answered before you agree — the specialist who looks after you should explain it, not a salesperson.
- Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
- You're entitled to your total cost in writing — including any follow-up — before you decide.
Questions to ask your medical professional
Take this to your consultation. A good specialist will welcome every one of these.
- What is my actual eGFR, and what does it mean in my situation?
- Could anything temporary have affected this result, and should it be repeated?
- Do I also need a urine test to check for protein or blood?
- How does this result compare with my previous ones — is it stable?
- Do any of my medicines need adjusting because of my kidney function?
- How often should I be retested, and what would prompt earlier testing?
- Are there 'sick-day rules' I should follow for my medicines if I become unwell?
- Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
- Will you be the specialist who carries out my test, and who looks after me afterwards?
- What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
- What does a realistic result look like — and what can this test not achieve?
- What are my options, including waiting, doing nothing for now, or choosing a different approach?
- Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
- What is the total cost in writing, including any follow-ups, and how much time do I have to decide?
Frequently asked questions
What is a normal eGFR?
My eGFR is a bit low — do I have kidney disease?
Do I need to fast before the test?
Why does a normal result still come with a urine test?
Can muscle or exercise affect my result?
Is this test available privately?
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How we made this page
Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →
Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.
Sources & standards: Kidney Care UK — Tests for chronic kidney disease UK Kidney Association — Measurement of kidney function (eGFR) Lab Tests Online UK — eGFR NHS — Chronic kidney disease (diagnosis) Kidney Research UK — Understanding test results NICE — Chronic kidney disease (NG203)
Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.
Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.
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