Blood test
Kidney Function Test (U&E)
A kidney function test is a blood test that checks how well your kidneys are filtering waste, using measures such as creatinine, urea and eGFR, along with salts (electrolytes).
Quick answer
Kidney Function Test (U&E): what it is and what the results mean
Often called "U&E" (urea and electrolytes), this blood test measures waste products such as creatinine and urea, the salts sodium and potassium, and calculates an estimated filtration rate (eGFR) that reflects how well the kidneys are working.
- Why it is done: It is used to check for and monitor kidney disease, to assess hydration and salt balance, before and during many medicines that affect the kidneys, and as part of general health and long-term-condition checks.
- Understanding results: A raised creatinine or a low eGFR can indicate reduced kidney function, while abnormal sodium or potassium can affect the heart and nerves and sometimes needs prompt attention.
What it is
Often called "U&E" (urea and electrolytes), this blood test measures waste products such as creatinine and urea, the salts sodium and potassium, and calculates an estimated filtration rate (eGFR) that reflects how well the kidneys are working.
Why it is done
It is used to check for and monitor kidney disease, to assess hydration and salt balance, before and during many medicines that affect the kidneys, and as part of general health and long-term-condition checks.
What to expect
A routine blood sample is taken from the arm; fasting is not usually required. It is frequently done alongside other blood tests at the same time.
Understanding the results
A raised creatinine or a low eGFR can indicate reduced kidney function, while abnormal sodium or potassium can affect the heart and nerves and sometimes needs prompt attention. Results are read together with your history, blood pressure and any urine tests.
Good to know
Risks and limitations
The test carries the minor risks of any blood test. A single result can be affected by dehydration or muscle mass, so kidney function is usually judged on trends over time rather than one reading.
Education and reference only. This explains the test in general terms and is not medical advice. Always follow the specific instructions from the team arranging your test, and discuss your results with your clinician.
Answers
Kidney Function Test (U&E): frequently asked questions
What is a normal eGFR?
An eGFR above 90 is generally considered normal, but what matters is the trend over time and your overall picture. Lower values can indicate reduced kidney function and are interpreted by your clinician.
Why check potassium and sodium?
These salts are vital for the heart, nerves and muscles. Levels that are too high or too low can cause symptoms and sometimes need urgent treatment, so they are checked alongside kidney function.
Related tests
Other blood test investigations
Sources
Where this is drawn from
- NHS — Tests and treatments
- NICE — diagnostic guidance
- Royal College of Pathologists / relevant professional body
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