What it measures
- Creatinine
- eGFR
- Urea
- Sodium
- Potassium
- Chloride
- Calcium
- Phosphate
What does a kidney function test measure?
Your kidneys filter waste from your blood and keep your salts and fluids in balance. This test measures:
- Creatinine and eGFR: eGFR (estimated glomerular filtration rate) is calculated from creatinine, age and sex and is the main measure of kidney filtration.
- Urea, another waste product.
- Electrolytes: sodium, potassium and chloride, which affect your muscles, nerves and heart rhythm.
- Calcium and phosphate, which the kidneys help regulate.
Kidney disease often has no symptoms until it’s advanced, so a simple blood test is the best way to spot changes early, especially if you have high blood pressure or diabetes.
Who it’s for
- High blood pressure or diabetes
- Taking medicines that affect the kidneys, such as some painkillers or blood pressure tablets
- Swelling, tiredness or changes in urination
- A family history of kidney disease
How to prepare
- Drink plenty of water beforehand; it makes the sample quicker and easier to take.
- You don’t need to fast.
- Avoid a large meat meal and very intense exercise in the 24 hours before.
Kidney Function Blood Test: your questions
What is a normal eGFR?
An eGFR of 90 or above is normal. Between 60 and 89 can be normal, especially as you get older, if there are no other signs of kidney damage. Below 60 on repeat tests suggests reduced kidney function.
Should I avoid anything before the test?
Avoid eating a large meat meal or doing very intense exercise in the 24 hours before, as both can raise creatinine slightly.
Information on this page is general and doesn’t replace advice from your GP, midwife or consultant. If you feel unwell or are worried about symptoms, contact your GP, call NHS 111 or, in an emergency, 999.