U&E is one of the most requested blood tests in hospitals. Small changes in sodium or potassium can be dangerous, so nurses need to know which results to escalate.
Imagine an older patient who seems more confused than yesterday. Nobody has looked at her bloods yet. Her sodium has dropped to 122. That number explains the confusion.
What U&E includes
- Sodium
- Potassium
- Urea
- Creatinine (often with eGFR)
- Sometimes bicarbonate and chloride
Typical adult ranges
- Sodium: about 135 to 145 mmol/L
- Potassium: about 3.5 to 5.0 or 5.3 mmol/L
- Urea: about 2.5 to 7.8 mmol/L
- Creatinine: varies with muscle mass, often about 60 to 110 µmol/L in men and lower in women
Why sodium matters
- Low sodium (hyponatraemia) can cause confusion, falls and seizures
- Causes include diuretics, vomiting, heart failure and some antidepressants
- High sodium (hypernatraemia) often means dehydration
Why potassium matters
- High potassium can cause dangerous heart rhythms
- Low potassium can cause weakness and arrhythmias
- Haemolysed (damaged) samples can falsely raise potassium
When to escalate
Very abnormal sodium or potassium results, or a sudden rise in creatinine, should be escalated urgently according to local policy.
Lab ranges vary
Reference ranges differ between laboratories and countries, and some use different units. Always compare your result with the range printed on your report and discuss it with your healthcare provider.
Why U&E is checked so often in hospital
Almost every patient admitted to hospital has a U&E on arrival, and many have it repeated daily. That is because fluids, illness and medicines can all change sodium, potassium and kidney function quickly.
Intravenous fluids, diuretics, blood pressure medicines, vomiting, diarrhoea, surgery and infection can all shift results within a day. Regular checks let healthcare providers adjust fluids and medicines before problems become dangerous.
Low sodium in more detail
Hyponatraemia is the most common electrolyte problem in hospital patients, especially older adults. Mild cases may cause no symptoms or only tiredness and unsteadiness, which can contribute to falls. Severe or rapidly falling sodium can cause confusion, vomiting, seizures and reduced consciousness.
Common causes include thiazide diuretics, some antidepressants (SSRIs), drinking very large amounts of fluid, heart failure, liver cirrhosis and a condition called SIADH, where the body holds on to too much water. Correcting sodium too quickly can itself cause harm, so treatment is carefully planned and monitored.
High potassium in more detail
Hyperkalaemia can cause muscle weakness, palpitations and dangerous heart rhythms, sometimes with few warning signs. It is more common in people with kidney disease and in those taking medicines such as ACE inhibitors, ARBs, spironolactone or potassium supplements.
If a result is very high, healthcare providers usually repeat the test, perform an ECG and may give emergency treatment to protect the heart and move potassium back into cells.
Low potassium in more detail
Hypokalaemia is often caused by diuretics, vomiting or diarrhoea. It can cause weakness, cramps, constipation and abnormal heart rhythms. Potassium can be replaced by mouth or through a drip. Intravenous potassium must always be given carefully, at safe rates and with appropriate monitoring, because mistakes can be fatal.
Getting an accurate sample
- Avoid prolonged tourniquet time and excessive fist clenching, which can raise potassium
- Do not take blood from an arm with an IV drip running
- Send samples promptly, as delays can falsely raise potassium
- Label samples correctly at the bedside
What the results mean for fluids
Urea and creatinine together can hint at dehydration. When urea rises much more than creatinine, it often suggests the person is dry or has been bleeding into the gut. Healthcare providers use these clues along with blood pressure, heart rate, urine output and the patient’s overall appearance to decide on fluids.
Nursing priorities
- Check results promptly and know your critical limits
- Escalate abnormal results with the patient’s observations and medicines
- Keep accurate fluid balance charts
- Review medicines that affect electrolytes
- Repeat tests at the times requested
High sodium in more detail
Hypernatraemia usually means the body has lost more water than salt. It is most common in frail older adults who cannot drink enough on their own, people with high fevers, and those with severe diarrhoea. Symptoms include thirst, confusion, irritability and, in severe cases, seizures.
Prevention is often simple: making sure water is within reach, offering drinks regularly and keeping accurate fluid charts. In care homes and hospital wards, these basic nursing actions can prevent a serious and sometimes fatal complication.
Acute kidney injury and U&E
A rise in creatinine of 1.5 times or more from a person’s baseline within a week, or a fall in urine output, can indicate acute kidney injury (AKI). Many laboratories now flag possible AKI automatically on U&E reports.
AKI is common in people who are unwell with infection, dehydration or after surgery, and it can often be reversed if caught early. Actions include treating the cause, reviewing medicines that can harm the kidneys, monitoring fluids carefully and checking U&E again.
Questions to ask about your results
- Which of my results are outside the normal range, and why?
- Do any of my medicines need to change?
- Do I need to drink more, or less, fluid?
- When will the test be repeated?
A note on units
Most countries report sodium and potassium in mmol/L, which is the same as mEq/L for these electrolytes. Creatinine is reported in µmol/L in the UK, Europe and many other countries, and in mg/dL in the US. One mg/dL of creatinine is about 88 µmol/L.
Electrolytes and older adults
Older adults are especially vulnerable to electrolyte problems. They often take several medicines that affect sodium and potassium, may feel less thirsty, and can become dehydrated quickly during hot weather or illness. Small changes, such as new confusion, a fall or unusual tiredness, can be the first sign. Checking U&E early, reviewing medicines and encouraging regular drinks can prevent serious harm.
Questions nurses can ask at handover
- When were the last U&E taken, and what were the results?
- Is the patient on any medicines that affect potassium or sodium?
- What is the fluid balance over the last 24 hours?
- Is a repeat test due?
Frequently asked questions
Why is my urea high?
Common causes include dehydration, kidney problems and bleeding in the stomach or bowel.
Do I need to fast for U&E?
Usually not.
What does “haemolysed sample” mean?
It means red blood cells broke down in the sample, releasing potassium and giving a falsely high result. The test usually needs repeating.
Can diet change potassium?
Yes, especially in kidney disease. Foods such as bananas, potatoes and tomatoes are high in potassium.
How quickly can sodium be corrected?
Slowly. Guidelines limit how fast sodium should rise in chronic hyponatraemia to avoid brain injury.
But the patient looks fine
Electrolyte problems can be silent until they become dangerous. Act on the results.
Your next step: Nurses: learn your hospital’s critical value limits for sodium and potassium.
Related: Sodium and potassium imbalances · Normal lab values cheat sheet
Sources: Lab Tests Online UK, Royal College of Pathologists, Society for Endocrinology, NHS.
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