Urea and Electrolytes (U&E) Blood Test Results Explained
U&E is the standard NHS panel for kidney function and fluid balance, sodium, potassium, urea, creatinine, chloride, bicarbonate and eGFR. Here's what each result means.
Based on clinical laboratory references
Reviewed by Dr. Prahlad Rai Gupta, MD
Free, no account needed
What a U&E test actually measures
One blood draw, seven numbers, the panel GPs order more than almost any other.
Na⁺ / K⁺
Sodium & potassium
The core electrolytes, fluid balance, nerve signalling, and heart rhythm.
Urea
Waste product
A byproduct of protein breakdown, filtered out by the kidneys.
Creatinine
+ eGFR
A muscle byproduct used to calculate how well your kidneys are filtering.
Urea and creatinine are both waste products your kidneys clear from the blood. When kidney function drops, both rise, but creatinine is the more reliable marker because, unlike urea, it isn't affected by diet, hydration, or protein intake. eGFR (estimated glomerular filtration rate) is calculated from your creatinine, age and sex, and gives the clearest single picture of kidney filtering capacity. If your report doesn't print an eGFR alongside creatinine, you can calculate it yourself with the free eGFR calculator.
U&E reference ranges
Standard adult ranges. Labs vary slightly, always check the range printed on your own report.
| Marker | Normal range | What it reflects |
|---|---|---|
| Sodium | 136 – 145 mmol/L | Fluid balance, blood pressure regulation |
| Potassium | 3.5 – 5.0 mmol/L | Heart rhythm, muscle and nerve function |
| Urea | 2.5 – 7.8 mmol/L | Protein breakdown, kidney clearance, hydration |
| Creatinine | 60 – 110 µmol/L (varies by sex) | Muscle breakdown product, kidney filtration |
| eGFR | > 90 mL/min/1.73m² | Estimated kidney filtration rate |
| Chloride | 98 – 106 mmol/L | Acid-base balance, works alongside sodium |
| Bicarbonate | 22 – 29 mmol/L | Acid-base (pH) balance |
High vs. low: what each direction means
U&E abnormalities rarely mean one thing in isolation, the pattern across markers points to the cause.
| Direction | What it means | Common causes | Note |
|---|---|---|---|
| High urea & creatinine, low eGFR | Reduced kidney function. When the kidneys filter less efficiently, waste products that should be cleared build up in the blood. This is the classic U&E pattern for declining kidney function. | Dehydration (most common reversible cause) · acute kidney injury, from infection, medication, or low blood pressure · chronic kidney disease (sustained low eGFR over 3+ months) · medications: NSAIDs, ACE inhibitors, diuretics · urinary tract obstruction | A raised urea with normal creatinine and eGFR is usually dehydration or a high-protein diet, not kidney disease, urea is the less specific of the two markers. |
| Abnormal sodium or potassium | Fluid balance or medication effect. Sodium and potassium abnormalities are usually driven by fluid shifts, medications, or, less commonly, hormonal or kidney causes. Potassium abnormalities are taken more seriously because of the heart-rhythm risk. | Low sodium: excess fluid intake, diuretics, heart or liver failure, SIADH · high sodium: dehydration, insufficient water intake · low potassium: diuretics, vomiting/diarrhoea, insufficient dietary intake · high potassium: kidney impairment, ACE inhibitors, tissue damage | Potassium above 6.0 mmol/L or below 2.5 mmol/L is usually flagged for urgent review, both extremes can affect heart rhythm. |
What to do next with an abnormal U&E
U&E is a screening panel, not a diagnosis, an abnormal result tells your doctor which direction to investigate further.
1
If kidney markers are abnormal (urea, creatinine, eGFR)
Check hydration first, a repeat test after rehydrating can normalise a borderline result. Review medications with your GP, particularly NSAIDs, ACE inhibitors, and diuretics. If eGFR stays below 60 on a repeat test 3 months later, this meets the threshold for chronic kidney disease and needs ongoing monitoring, use the eGFR calculator to track it from your creatinine over time. Compare against high creatinine for a deeper look at that specific marker.
2
If sodium or potassium are abnormal
Mild abnormalities are often retested before any action is taken, single readings can be affected by sample handling. Significant potassium abnormalities (very high or very low) usually prompt an ECG to check heart rhythm. Review diuretics, supplements, and recent vomiting or diarrhoea as common reversible causes. Persistent abnormalities without an obvious cause may need hormonal or kidney work-up.
Frequently asked questions
What is a normal urea and electrolytes level?
Typical adult reference ranges are: sodium 136–145 mmol/L, potassium 3.5–5.0 mmol/L, urea 2.5–7.8 mmol/L, creatinine 60–110 µmol/L (varies by sex), chloride 98–106 mmol/L, and bicarbonate 22–29 mmol/L. Every lab sets its own ranges based on its testing equipment, so always check the figures printed next to your result on the report rather than relying on generic numbers.
What level of urea is concerning?
Urea above roughly 7.8 mmol/L is flagged as high, but a single raised urea reading is rarely concerning on its own, dehydration, a high-protein meal, or gastrointestinal bleeding can all push it up temporarily. Urea becomes more concerning when it rises alongside creatinine and a falling eGFR, which together point toward reduced kidney function, or when it is markedly elevated (above roughly 15–20 mmol/L) with symptoms like confusion or reduced urine output.
Why would urea and electrolytes be abnormal?
The most common causes are dehydration, medications (particularly diuretics, ACE inhibitors and NSAIDs), kidney disease, and gastrointestinal fluid losses such as vomiting or diarrhoea. Hospital inpatients often show abnormal U&Es from IV fluids or acute illness. Because sodium, potassium, urea and creatinine all interact with each other, the pattern across all four values, not any single number in isolation, points toward the likely cause.
What are four signs of an electrolyte imbalance?
Common signs include muscle cramps or weakness, irregular heartbeat (particularly with abnormal potassium), confusion or fatigue (often linked to abnormal sodium), and nausea or swelling (linked to fluid balance disturbances). Severe imbalances, especially of potassium, can affect heart rhythm and need urgent medical attention. Mild imbalances are often picked up on a routine U&E test before any symptoms appear at all.
What's the difference between urea and creatinine?
Both are waste products cleared by the kidneys, but creatinine is the more reliable marker of kidney function. Urea levels are affected by diet (protein intake), hydration, and gastrointestinal bleeding, which makes it less specific. Creatinine comes from normal muscle breakdown at a fairly constant rate, so it tracks kidney filtration more accurately, this is why eGFR (the standard kidney-function calculation) is based on creatinine, not urea.
Is U&E the same as a kidney function test?
U&E includes the core kidney function markers (urea, creatinine, eGFR) alongside electrolytes (sodium, potassium, chloride, bicarbonate) that aren't strictly kidney-specific but are commonly affected by kidney problems. Some labs and clinicians use "kidney function test" and "U&E" interchangeably, though a dedicated renal panel may add extra markers like phosphate or calcium that a standard U&E doesn't always include.
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