U&E Blood Test Results Explained: Urea, Sodium, Potassium, eGFR
U&E stands for urea and electrolytes. It’s the UK’s routine blood test of sodium, potassium, urea, creatinine and eGFR. UK harmonised adult ranges are sodium 133–146 mmol/L, potassium 3.5–5.3 mmol/L and urea 2.5–7.8 mmol/L. The US equivalent is the basic metabolic panel (BMP), which reports urea as BUN in mg/dL. A high potassium can be a false reading from a damaged or delayed sample, but UK guidance sends a potassium of 6.5 mmol/L or more for hospital assessment straight away.
Units: sodium, potassium, chloride and bicarbonate give the same number in mmol/L and mEq/L. Urea (mmol/L) × 2.80 = BUN (mg/dL). Creatinine (µmol/L) ÷ 88.4 = mg/dL.
- What’s in a U&E
- UK vs US units
- High potassium
- High urea
- Kidney pattern
- Medicines
- Low sodium
- Same-day results
- NHS App and flags
What a U&E includes, line by line
A U&E (also U+E, U/E or renal profile) is a set of tests on one tube of blood.
| Test | What it tells you | Typical UK adult range | US BMP line, example range |
|---|---|---|---|
| Sodium | Salt and water balance | 133–146 mmol/L | Sodium: 135–145 mmol/L |
| Potassium | Nerve, muscle and heart signalling | 3.5–5.3 mmol/L* | Potassium: 3.6–5.2 mmol/L |
| Urea | Waste from protein. Also rises with dehydration | 2.5–7.8 mmol/L | BUN: 8–24 mg/dL (men), 6–21 (women) |
| Creatinine | Waste from muscle, and the main clue to kidney filtering | Men 59–104, women 45–84 µmol/L | Men 0.74–1.35, women 0.59–1.04 mg/dL |
| eGFR | Filtering rate, estimated from creatinine, age and sex | Above 90 is shown as “>90” | Same unit. Mayo’s reference is 60 or more |
| Chloride | Read with sodium and bicarbonate | 95–108 mmol/L | Chloride: 98–107 mmol/L |
| Bicarbonate | Acid-base balance | 22–29 mmol/L | Bicarbonate or “CO2”: 22–29 mmol/L |
| Glucose, calcium | Blood sugar and calcium | Separate tests, not in a U&E | In every BMP |
UK: Pathology Harmony; creatinine from North Bristol NHS Trust. *Some labs use an upper limit of 5.0 or 5.1. US: Mayo Clinic Laboratories (Labcorp differs slightly). Your own report’s range comes first.
Some UK labs leave urea out of GP requests unless asked (North Bristol, Gloucestershire), and add chloride and bicarbonate only on request. A US BMP always has eight tests, including glucose and calcium (MedlinePlus). A comprehensive metabolic panel (CMP) adds six more, such as albumin and liver enzymes.
U&E vs BMP: converting the units
Most lines give the same number in both countries. Only urea and creatinine need converting.
| Result | UK unit | US unit | How to convert | Example |
|---|---|---|---|---|
| Sodium, potassium, chloride, bicarbonate, eGFR | mmol/L (eGFR: mL/min/1.73m²) | Same unit, or mEq/L | No conversion | K 4.2 = 4.2 |
| Urea vs BUN | urea, mmol/L | BUN, mg/dL | Urea × 2.80 = BUN BUN × 0.357 = urea | Urea 6.0 = BUN 16.8 BUN 14 = urea 5.0 |
| Creatinine | µmol/L | mg/dL | µmol/L ÷ 88.4 = mg/dL | 100 = 1.13 |
BUN (blood urea nitrogen) counts only the nitrogen in urea, so the numbers differ. The UK urea range of 2.5–7.8 mmol/L is a BUN of about 7–22 mg/dL (Labcorp factors). For other tests, try our blood test unit converter.
What a U&E actually tells you
Think of a U&E as five witnesses to one scene. Any one of them can mislead. Together, they usually agree on a story.
- Creatinine and eGFR show how well your kidneys filter. Creatinine, from muscle, builds up when filtering slows. See our kidney function test guide.
- Urea rises with kidney problems, but also with dehydration, gut bleeding, a high-protein meal and steroids (Labcorp), so it’s read alongside creatinine (Mayo).
- Sodium can rise with dehydration and fall with some medicines, heart failure and hormone problems (Labcorp). See sodium levels.
- Potassium matters because a severely high level risks dangerous heart rhythms (UK Kidney Association). Low potassium can follow diuretics, diarrhoea or vomiting (MedlinePlus), or point to excess aldosterone (Labcorp). See potassium levels.
Common U&E patterns
Each card gives clues, usual suspects, next lead and what guidelines say.
High potassium, everything else normal
Two suspects: the sample and the body. The sample is checked first.
- Potassium above your lab’s range
- Creatinine and eGFR normal
- Sometimes a lab note that the sample was haemolysed or delayed
- A false high from the sample (see what can throw off a U&E)
- Medicines such as ACE inhibitors, ARBs, spironolactone, NSAIDs or trimethoprim
- Reduced kidney function
A repeat sample that reaches the lab quickly.
UKKA 2026: mild 5.5 to 5.9 (repeat within 3 days), moderate 6.0 to 6.4 (repeat within 1 day), severe 6.5 or more (hospital now). Acutely unwell? Any of these needs hospital assessment.
Ask: Could this be a sample problem? When should I repeat it? Do any of my medicines raise potassium?
High urea, with creatinine normal or slightly raised
Even moderate dehydration can raise urea, and dehydration can also raise sodium (Labcorp). Creatinine shows whether filtering has changed.
- Urea above range
- Sodium normal or high
- Recent vomiting, diarrhoea, fever or drinking little
- Dehydration
- Bleeding in the stomach or gut
- Heart failure, steroids or a recent high-protein meal (Labcorp; Mayo)
A repeat U&E. If creatinine has risen too, see the kidney pattern.
Seen in normal pregnancy, with a low protein intake, with intravenous fluids and in some liver disease (Labcorp).
Ask: Was I dehydrated? Should we repeat it? Any sign of bleeding?
Creatinine up, eGFR down
The key question is speed. A sudden change points to acute kidney injury (AKI). A slow drift over months fits chronic kidney disease (CKD).
- Creatinine above range, or higher than last time
- eGFR lower; urea and potassium often up
- In England, an “AKI stage” beside creatinine
- AKI from dehydration, low blood pressure or blood loss (NHS)
- NSAIDs, ACE inhibitors, ARBs or diuretics (NICE NG148)
- CKD
- False alarms: meat or a very muscular build (see pitfalls)
Comparison with earlier results. NICE flags AKI at a creatinine rise of 26 µmol/L (about 0.3 mg/dL) or more within 48 hours, or 50% within 7 days.
A first-ever eGFR below 60 is repeated within 2 weeks. CKD means changes lasting more than 3 months (NICE NG203).
Ask: Is this sudden or gradual? Could my medicines be involved? When should it be repeated?
After starting an ACE inhibitor, ARB or diuretic
These medicines can move several lines at once, so they come with blood tests.
- A small creatinine rise and slightly higher potassium after an ACE inhibitor or ARB
- Lower sodium or potassium on a diuretic
- ACE inhibitors, ARBs, spironolactone and amiloride can raise potassium (UKKA)
- Diuretics can lower potassium (MedlinePlus)
- Thiazides are a frequent cause of low sodium, loop diuretics less so (European guideline)
In CKD, NICE advises checking potassium and eGFR before an ACE inhibitor or ARB, then 1 to 2 weeks after starting or a dose increase.
NICE NG203: no dose change for an eGFR fall under 25% or a creatinine rise under 30%. Doctors stop them at a potassium of 6.0 or more once other potassium-raising medicines are stopped.
Ask: Is this change expected? When is my next test? What should I do with my tablets if I’m vomiting? Don’t stop a prescribed medicine without advice.
Low sodium (hyponatremia)
European guidance defines hyponatremia (hyponatraemia, UK spelling) as sodium below 135 mmol/L. UK lab ranges start at 133. Symptoms depend more on how fast sodium fell than on the number (Mayo).
- Mild: 130 to 135. Moderate: 125 to 129. Profound: below 125 (European guideline 2014)
- Possibly nausea, headache or confusion
- Thiazides and other medicines
- Heart failure, kidney disease, an underactive thyroid, or SIADH, a hormone problem that holds on to water (Labcorp)
- A false low from very high triglycerides or protein
A repeat and a medicine review. See sodium levels.
Labs phone 120 or below urgently (RCPath 2026). Vomiting, seizures or deep drowsiness are severe symptoms (European guideline).
Ask: How fast has it dropped? Could a medicine be causing it? Do I need other tests?
What can throw off a U&E result
A careful detective checks for planted evidence first. Potassium is the easiest line to plant, because blood cells are full of it.
- Haemolysis. Red cells damaged during the draw spill potassium into the sample (North Bristol; RUH Bath). Badly haemolysed samples may be rejected (Labcorp; Mayo).
- Delay or cold. Potassium rises if blood waits too long before separation, or is refrigerated first (RUH Bath; Labcorp). University Hospitals Sussex won’t analyse samples over 8 hours old.
- Tube order. EDTA from a full blood count tube can contaminate the sample, so some labs ask for the U&E tube first (Gloucestershire; RUH Bath).
- Fist clenching or a long tourniquet can raise potassium (Labcorp; MedlinePlus).
- Very high platelets or white cells can release potassium in the tube (Labcorp). A lithium heparin tube is more accurate (RUH Bath). See platelet count and white blood cell count.
- Meat and muscle. NICE advises no meat for 12 hours before an eGFR test, and caution with extremes of muscle mass.
- Very high triglycerides or protein can make sodium read falsely low on some analyzers (Labcorp).
- An open tube lets carbon dioxide escape, which lowers bicarbonate (Labcorp).
Pregnancy, older age and children
Pregnancy. Kidney filtering rises by 30 to 50%. Urea usually falls below about 3.6 mmol/L (BUN 10 mg/dL), and creatinine to about 44–62 µmol/L (0.5–0.7 mg/dL) (Merck Manual). So a creatinine in the standard range can be relatively high. Ask your maternity team.
Older adults. eGFR tends to fall with age, and low muscle mass can make creatinine look reassuring (see kidney guide). Children have different ranges and alert levels (RCPath).
Reading a U&E on your lab report or the NHS App
- Names: U&E, U+E, U/E, urea and electrolytes, or renal profile. In the US, a BMP or CMP. Bicarbonate may show as CO2, total CO2 or TCO2 (MedlinePlus).
- Flags: “H” or “L” means outside that lab’s range, not a diagnosis.
- eGFR “>90”: how UK labs report anything above 90 (NICE).
- AKI warning stage: in England, the lab compares your creatinine with earlier results and may print “AKI stage 1, 2 or 3” beside it (Think Kidneys). Stage 1 means at least 1.5 times your usual level, stage 2 at least 2 times, and stage 3 at least 3 times or a rise to above 354 µmol/L.
- Lab comments: a haemolysed or delayed sample note means potassium may be unreliable. Ask about a repeat.
- NHS App: results usually appear within a few days, sometimes before anyone has discussed them with you (NHS). A GP practice comment, if there is one, gives their view on next steps; NHS England asks for abnormal results needing no action to be explained in plain words. Hospital results may show in Patients Know Best instead. If you’re worried, contact your GP practice.
- US portals: results often appear before your clinician has commented.
Which U&E results need same-day action
UK labs phone these results to the requesting doctor within 2 hours (RCPath 2026, adults). Local limits can differ, especially with known kidney disease.
| Result | Phoned urgently if (UK units) | Same level in US units |
|---|---|---|
| Potassium | 2.5 or less, or 6.5 or more mmol/L | Same numbers in mEq/L |
| Sodium | 120 or less, or 160 or more mmol/L | Same numbers in mEq/L |
| Urea | 30 mmol/L or more | BUN about 84 mg/dL or more |
| Creatinine | 354 µmol/L or more | About 4.0 mg/dL or more |
| AKI warning stage | Stage 2 or 3 | Not used on US reports |
For potassium, the lab first rules out haemolysis, an old sample or EDTA contamination (RCPath). US labs set their own critical values; Mayo Clinic Laboratories calls potassium below 2.5 or above 6.0 mmol/L potentially life-threatening.
Sources: Pathology Harmony; Mayo; UKKA 2026.
When to get help urgently
- You’ve been told your potassium is 6.5 mmol/L or more, or told to go to hospital: go now (UK Kidney Association).
- Any abnormal U&E and a very slow, fast or irregular heartbeat, new muscle weakness, confusion, severe drowsiness, a seizure or repeated vomiting: call 999 (UK) or 911 (US).
- Signs of acute kidney injury, such as peeing much less than usual, feeling very thirsty, confused or sleepy, or breathless when lying down: get an urgent GP appointment or call NHS 111 (NHS). In the US, get same-day care.
U&E questions people ask
What does U&E stand for?
Urea and electrolytes. It’s a UK blood test of sodium, potassium, urea, creatinine and eGFR, also called a renal profile.
What are normal U&E results?
UK harmonised adult ranges are sodium 133–146 mmol/L, potassium 3.5–5.3 and urea 2.5–7.8. Creatinine depends on sex and lab. Use the range on your report.
Is a U&E the same as a BMP?
Nearly. A US basic metabolic panel has the same core tests plus glucose, calcium, chloride and CO2 (bicarbonate), and reports BUN and creatinine in mg/dL.
What does a high urea mean?
Common causes include dehydration, reduced kidney function, gut bleeding, a high-protein meal and steroids (Labcorp). Creatinine helps tell these apart.
Why is my potassium high when I feel fine?
It may be a false reading from a damaged, delayed or chilled sample, or from fist clenching. It can also be real, so it’s repeated: within 3 days for 5.5 to 5.9, and within 1 day for 6.0 to 6.4 (UK Kidney Association).
How do I convert urea to BUN?
Multiply urea in mmol/L by 2.80 to get BUN in mg/dL. A urea of 5.0 mmol/L is a BUN of 14 mg/dL.
Do I need to fast for a U&E?
NICE advises no meat for 12 hours before an eGFR test. A US BMP includes glucose, so you may need to fast for 8 hours (MedlinePlus).
How we wrote this page
Written and medically reviewed by Dr. Mustafa Sakr, MBBCh. Last reviewed: October 2026. The numbers come from current UK guidance (Royal College of Pathologists, UK Kidney Association, NICE) and published UK and US lab reference ranges, listed below. We update this page when guidance changes.
How we chose the numbers: UK ranges are Pathology Harmony adult ranges unless stated. US ranges are Mayo Clinic Laboratories examples. Conversions use Labcorp’s factors. There’s no checker, because a U&E is read as a set, with your history.
References
- Royal College of Pathologists. The communication of critical and unexpected pathology results (G158), 2026. rcpath.org (PDF)
- UK Kidney Association. Treatment of Acute Hyperkalaemia in Adults, updated July 2026. ukkidney.org (PDF)
- NICE. Acute kidney injury (NG148), updated 2024. nice.org.uk
- NICE. Chronic kidney disease (NG203), 2021. nice.org.uk
- Spasovski G, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. Eur J Endocrinol 2014;170(3):G1–G47. doi:10.1530/EJE-13-1020
- Pathology Harmony Group. Agreed Adult Clinical Biochemistry Reference Intervals, 2011. labmed.org.uk
- NHS lab directories: North Bristol (creatinine, potassium, urea); Worcestershire; Gloucestershire; University Hospitals Sussex.
- Royal United Hospitals Bath. Hyperkalaemia: a guide for GPs, 2024. ruh.nhs.uk (PDF)
- Think Kidneys. Responding to AKI Warning Stage Test Results in Primary Care, 2018. thinkkidneys.nhs.uk (PDF)
- Mayo Clinic Laboratories: sodium, potassium, chloride, bicarbonate, BUN, creatinine.
- Labcorp: BMP, potassium, sodium, BUN, total CO2, SI conversion table.
- MedlinePlus, 2024: BMP, potassium, CO2.
- NHS: Acute kidney injury, 2026; NHS App test results, 2026. NHS England: patient access to new health information.
- Merck Manual Professional. Physiology of Pregnancy, 2024. merckmanuals.com
This page is for education only and isn’t medical advice, a diagnosis or a substitute for your own doctor, who knows your history. Reference ranges vary between laboratories. Always interpret results with a qualified clinician. See our medical disclaimer.
