Kidney markers
U&E Results Explained: What Your Kidney Numbers Mean
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed September 20267 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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A U&E report carries five numbers. Sodium and potassium are salts that keep your body's water and nerve signals in balance. Urea and creatinine are waste products your kidneys clear. eGFR is a calculated score for how fast they are clearing them. Read together they describe kidney function and hydration.
Not sure which markers you need? Build your test →You have the printout in front of you. Five rows, five numbers, one of them with an H or an L beside it, and no sentence anywhere explaining what any of it means.
U&E stands for urea and electrolytes. It is the most commonly ordered blood test in the NHS, and it is really a test of two things at once: how your kidneys are working, and how your body is handling water and salt.
1. What is on a U&E report?
Usually five results, sometimes four if eGFR has not been calculated. The ranges below are the ones South Tees Hospitals publishes. Your own lab may print slightly different figures, and its range is the one your result was judged against.
One thing no lab prints is your age, and urea is the line it matters most for. See urea levels by age for what a healthy reading looks like in each decade.
| Marker | Adult range | In one line |
|---|---|---|
| Sodium | 133 to 146 mmol/L | Water and salt balance |
| Potassium | 3.5 to 5.3 mmol/L | Nerve and heart signalling |
| Urea | 2.5 to 7.0 mmol/L | Waste from protein breakdown |
| Creatinine | 50 to 120 µmol/L | Waste from muscle |
| eGFR | Above 90 ml/min | Calculated filtering speed |
The eGFR figure comes from the NHS, which says healthy kidneys should be able to filter more than 90ml a minute. The other four come from South Tees.
A U&E often arrives with a full blood count printed beside it. The two get ordered together so routinely that many people assume they are one test.
2. What is each number telling you?
Sodium
Sodium is the main salt in the fluid outside your cells, and your body holds it in a narrow band. A low sodium usually says more about water than about salt. Drinking a great deal, some medicines and certain illnesses all dilute it.
Potassium
Potassium sits mostly inside your cells and matters for how nerves and muscle fire, the heart included. It is also the result most easily spoiled by the sample itself. If red cells break during collection they leak potassium, which reads as a high result that was never really there. A repeat is the usual answer.
Urea
Urea is what your liver makes when it breaks protein down, and your kidneys clear it. South Tees notes that raised levels are associated with kidney failure, dehydration, chronic heart failure and bleeding into the gut. Low levels go with pregnancy and a low protein diet, and our guide to low urea levels covers the rest.
Urea moves with hydration faster than creatinine does. A urea that is up while creatinine is normal often points at fluid rather than kidneys. Our guide to normal urea levels goes into where the figure sits by age.
Creatinine
Creatinine is waste from ordinary muscle activity, produced at a fairly steady rate. That steadiness is what makes it useful. It is also why muscle mass changes it: a big, muscular adult runs a higher creatinine than a small one with identical kidneys. Our guide on creatinine levels by age has the detail.
3. Why is eGFR the number people misread?
Because it is not measured. It is calculated, from your creatinine plus your age and sex. It estimates how many millilitres of waste your kidneys filter a minute, and the word estimate is doing real work there.
A single figure under 60 is where people panic. NICE is clear that one reading is not the end of it:
“Confirm an eGFR result of less than 60 ml/min/1.73 m2 in an adult not previously tested by repeating the test within 2 weeks.”
NICE guideline NG203, recommendation 1.1.8
NICE also asks that changes in eGFR be read allowing for the natural variation in creatinine, which it puts at about 5 per cent. So a score that moves from 88 to 84 has probably not moved at all.
One more caution from the same guideline. It says eGFR values of 60 and above should be interpreted with care, because the estimate gets less accurate as true kidney function rises. Our guide to eGFR levels by age explains why a score in the 70s is ordinary in later life.
4. What makes a U&E look worse than it is?
Quite a lot, and this is the part worth knowing before you lose an evening to it. NICE lists situations where the eGFR estimate is less reliable, and two of them are ordinary life rather than illness.
- A lot of muscle, or protein supplements. NICE names both. More muscle means more creatinine, which drags the estimate down.
- Dehydration. Urea climbs first, and creatinine follows.
- A hard training session. Muscle turnover lifts creatinine for a while.
- Pregnancy. NICE lists it among the states where the estimate is less reliable.
- Some medicines. Several change kidney numbers without changing kidney function.
Creatine supplements are a common one people miss. Our guide on whether creatine raises creatinine covers what the research shows, and dehydration and blood test results covers the other big one. If it is the urea that is flagged, our guide to high urea levels takes that number on its own.
None of this means a flagged result should be ignored. It means the sensible next step is a repeat in normal conditions, not a night of searching.
5. Which of these does Helvy measure?
Three of the five. The Thyroid & Vital Organs panel carries urea, creatinine and eGFR, read alongside your liver markers, albumin and your thyroid hormones. General Energy & Wellness carries urea and creatinine in a broader first look.
The honest limit is the other two. No Helvy panel measures sodium or potassium. If those are the numbers you want watched, that is a conversation with your GP rather than something we can help with. Both tests are home finger-prick kits processed by UKAS-accredited UK labs.
What a home test does give you is the comparison. One creatinine is a snapshot, and two taken months apart in similar conditions say far more. Our guide to kidney function tests walks the wider picture. If you are unsure which panel fits, the build-my-test tool takes about a minute.
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See your kidney markers with the context the printout leaves out
Helvy's home blood tests report urea, creatinine and eGFR with the context the printout leaves out, so a figure near the edge of a range never sparks a needless panic. Samples are processed by UKAS-accredited UK labs.
Frequently asked questions
What does U&E stand for on a blood test?
Urea and electrolytes. In practice it means sodium, potassium, urea and creatinine, usually with a calculated eGFR score alongside them.
What are normal U&E results in the UK?
South Tees publishes sodium 133 to 146 mmol/L, potassium 3.5 to 5.3 mmol/L, urea 2.5 to 7.0 mmol/L and creatinine 50 to 120 µmol/L for adults. The NHS puts healthy filtering above 90ml a minute.
Is an eGFR of 58 a problem?
It is below the 60 line, so NICE advises repeating the test within two weeks to confirm it before anything is concluded. One reading on its own does not settle the question.
Can dehydration affect U&E results?
Yes. South Tees lists dehydration among the causes of a raised urea. Urea tends to climb before creatinine does, so a high urea with a normal creatinine often points at fluid.
Does muscle or protein powder change these numbers?
NICE names higher muscle mass and protein supplements among the situations where the eGFR estimate is less reliable. More muscle produces more creatinine, which lowers the calculated score.
Why was my potassium high on one test and normal on the next?
Potassium leaks out of red blood cells if they break during collection, which reads as a high result. A repeat sample is the standard way to check.
Does Helvy test sodium and potassium?
No. Our panels carry urea, creatinine and eGFR, but not sodium or potassium. If you want those watched, speak to your GP.
Do I need to fast for a U&E test?
Not usually. Hydration matters more than food for these markers, so drinking normally in the hours before the sample is the more useful thing to get right.
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