A U&E blood test, also called urea and electrolytes, is one of the most common blood tests used in the UK. It helps check your kidney function, your salt and fluid balance, and sometimes whether dehydration, medicines or illness may be affecting your body chemistry.
Although it sounds technical, a U&E result is usually built around a small group of markers: sodium, potassium, urea, creatinine and often eGFR. Some reports also include chloride and bicarbonate. Together, they give a snapshot of how well your kidneys are filtering waste, how balanced your body fluids are, and whether there are electrolyte changes that need attention.
This guide explains what each result means, what can cause high or low levels, when abnormal U&E results are urgent, and what usually happens next.
Important: Blood test reference ranges vary between laboratories, and results must be interpreted alongside your symptoms, medicines, medical history and previous results. This article is for general information only and should not replace medical advice from your GP, specialist or the clinician who arranged your test.
What does U&E stand for?
U&E stands for urea and electrolytes. In everyday practice, it is often used as a shorthand for a kidney function blood test. The exact markers included can vary slightly between laboratories, but a typical U&E profile includes:
- Sodium — one of the main salts in the blood, important for fluid balance, nerves and muscles.
- Potassium — important for muscle, nerve and heart rhythm function.
- Urea — a waste product made from protein breakdown and cleared by the kidneys.
- Creatinine — a waste product from muscle metabolism, used to estimate kidney filtration.
- eGFR — estimated glomerular filtration rate, a calculation of how well your kidneys are filtering blood.
- Chloride — another electrolyte involved in fluid and acid-base balance.
- Bicarbonate — helps show the body’s acid-base balance.
The NHS describes an electrolyte test as a blood test used to check for an electrolyte imbalance, including minerals such as sodium, potassium, chloride and bicarbonate. In many UK settings, U&Es are also used to assess kidney function before surgery, during hospital admissions, while monitoring long-term conditions, or before and after starting certain medicines.
Why might a U&E blood test be done?
U&Es are requested for many reasons. Sometimes they are part of a routine blood panel. Other times, they are ordered because a doctor wants to check whether your kidneys, fluid levels or medicines may be contributing to symptoms.
Common reasons include:
- checking kidney function as part of a general health review;
- investigating tiredness, weakness, confusion, dizziness, vomiting or dehydration;
- monitoring high blood pressure, diabetes, heart failure or chronic kidney disease;
- checking whether medicines are affecting kidney function or potassium levels;
- monitoring people taking ACE inhibitors, ARBs, diuretics, spironolactone, lithium, NSAIDs or some antibiotics;
- checking safety before scans using contrast dye, operations or certain treatments;
- following up an abnormal urine test, blood pressure result or previous kidney blood test.
If you are trying to understand a wider set of results, you may also find these guides useful: How to Understand Blood Test Results, Kidney Blood Test Results Explained and Urine Test Results Explained.
What do U&E results show?
A U&E test does not diagnose one single condition on its own. Instead, it helps answer several practical questions:
- Are the kidneys filtering normally? Creatinine and eGFR are the main markers here.
- Is there evidence of dehydration or reduced blood flow to the kidneys? Urea and creatinine patterns can help.
- Are sodium or potassium levels abnormal? These can be affected by illness, medicines, kidney problems, hormones and fluid balance.
- Is there an acid-base disturbance? Bicarbonate and chloride can give clues, especially in more unwell patients.
- Is this a new problem or a long-term pattern? Comparing with previous results is often more useful than looking at one number in isolation.
Typical U&E reference ranges
Reference ranges vary by laboratory, age, sex, pregnancy status, sample type and clinical context. Always use the range printed next to your own result. The table below gives a broad guide only.
| Marker | What it broadly reflects | Typical adult reference range |
|---|---|---|
| Sodium | Fluid and salt balance | About 133–146 mmol/L |
| Potassium | Heart, muscle and nerve function | About 3.5–5.3 mmol/L |
| Urea | Protein waste product cleared by kidneys | About 2.5–7.8 mmol/L |
| Creatinine | Waste product used to estimate kidney filtration | Varies by sex, age and muscle mass |
| eGFR | Estimated kidney filtration rate | Often reported as above or below 60 mL/min/1.73m² |
| Chloride | Fluid and acid-base balance | About 95–108 mmol/L |
| Bicarbonate | Acid-base balance | About 22–29 mmol/L |
A mildly abnormal result is not always dangerous. For example, a slightly raised urea may occur after dehydration, a high-protein diet or temporary illness. A mildly reduced eGFR may need repeating before anyone can say whether it represents chronic kidney disease. On the other hand, some electrolyte abnormalities, especially significant potassium changes, can need urgent attention.
Sodium blood test result explained
Sodium is one of the main electrolytes in the blood. It helps regulate fluid balance and is important for normal nerve and muscle function. Sodium is closely linked to how much water is in the body, so abnormal sodium results often reflect a water balance problem rather than a simple “salt intake” problem.
Low sodium: hyponatraemia
Low sodium is called hyponatraemia. It can be mild and found incidentally, or it can be serious, especially if it develops quickly or is very low.
Possible causes of low sodium include:
- drinking excessive amounts of water, especially during illness or endurance exercise;
- vomiting, diarrhoea or dehydration;
- heart failure, liver disease or kidney disease;
- some medicines, including certain antidepressants, diuretics and epilepsy medicines;
- hormonal problems, including adrenal insufficiency or thyroid disease;
- SIADH, a condition where the body retains too much water.
Symptoms of low sodium can include headache, nausea, tiredness, confusion, muscle cramps, drowsiness and, in severe cases, seizures. Symptoms matter a lot: someone with a slightly low sodium and no symptoms may be managed very differently from someone who is confused or acutely unwell.
High sodium: hypernatraemia
High sodium is called hypernatraemia. It often suggests the body has too little water compared with sodium. This may happen with dehydration, reduced fluid intake, fever, severe sweating, diarrhoea, vomiting, poorly controlled diabetes, or problems with thirst and access to fluids.
Older adults, babies, people with dementia and people who are very unwell are more vulnerable because they may not be able to drink enough or communicate thirst.
Potassium blood test result explained
Potassium is one of the most important results in a U&E panel because it affects the electrical activity of the heart. Both high and low potassium can be significant, especially if the abnormality is large, new, or linked with symptoms.
High potassium: hyperkalaemia
High potassium is called hyperkalaemia. It can happen when the kidneys cannot remove potassium effectively, when potassium shifts out of cells, or when medicines raise potassium levels.
Common causes include:
- reduced kidney function or acute kidney injury;
- ACE inhibitors or ARBs, often used for blood pressure, heart disease or kidney protection;
- spironolactone, eplerenone or amiloride;
- potassium supplements or potassium-containing salt substitutes;
- NSAIDs such as ibuprofen or naproxen, especially in people with kidney risk factors;
- dehydration or severe illness;
- a blood sample problem, sometimes called pseudohyperkalaemia.
High potassium may cause no symptoms, which is why it can be picked up unexpectedly on a blood test. When symptoms occur, they can include weakness, palpitations, chest discomfort, faintness or feeling generally very unwell.
Several NHS hyperkalaemia guidance documents advise urgent assessment for markedly raised potassium, especially around 6.5 mmol/L or above, or where there are ECG changes or concerning symptoms. If your result is significantly raised, do not try to manage it yourself with diet alone. Follow the advice of the laboratory, GP, out-of-hours service or hospital team.
For patient information about high potassium, Kidney Research UK has a helpful overview of hyperkalaemia.
Low potassium: hypokalaemia
Low potassium is called hypokalaemia. It can affect muscles and the heart, particularly if the level is very low or if you have heart disease or take certain medicines.
Possible causes include:
- vomiting or diarrhoea;
- diuretics, sometimes called water tablets;
- laxative overuse;
- poor intake during illness;
- some hormonal conditions, including high aldosterone states;
- shifts of potassium into cells, which can happen in some medical situations.
Symptoms can include muscle weakness, cramps, constipation, palpitations or tiredness. Treatment depends on the cause and severity. Do not start potassium supplements unless a clinician has advised it, because too much potassium can be dangerous.
Urea blood test result explained
Urea is a waste product made when the body breaks down protein. It is made in the liver and removed from the blood by the kidneys. Urea can rise when the kidneys are not clearing waste normally, but it is also affected by hydration, diet and bleeding in the gut.
High urea
A high urea result can be caused by:
- dehydration;
- reduced kidney function;
- acute kidney injury;
- a high-protein diet or increased protein breakdown;
- gastrointestinal bleeding;
- heart failure or reduced blood flow to the kidneys;
- some medicines.
Urea is often interpreted alongside creatinine. If urea is high but creatinine is normal, dehydration, diet or gut bleeding may be considered depending on the context. If both urea and creatinine are high, the kidneys may not be filtering normally, or there may be reduced blood flow to the kidneys.
Because urea can be influenced by many non-kidney factors, it is rarely interpreted alone. It is most useful when viewed with creatinine, eGFR, symptoms, urine tests and previous results.
Low urea
Low urea is less commonly a concern. It may be seen with low protein intake, overhydration, pregnancy, or some liver-related conditions. A low urea result is usually interpreted in the wider clinical picture rather than treated by itself.
Creatinine blood test result explained
Creatinine is a waste product produced by muscles. Your kidneys filter creatinine out of the blood, so it is used as a marker of kidney function. However, creatinine is strongly affected by muscle mass.
This means a creatinine result that is “normal” for one person may not be ideal for another. A muscular young adult may naturally have a higher creatinine than a smaller older adult. Someone with low muscle mass may have a deceptively low creatinine even if kidney function is not perfect.
High creatinine
A high creatinine result can suggest reduced kidney filtration, but the cause may be temporary or long term. Possible causes include:
- dehydration;
- acute kidney injury;
- chronic kidney disease;
- urinary blockage, such as severe prostate enlargement or kidney stones;
- recent intense exercise or muscle injury;
- some medicines, including NSAIDs and certain antibiotics;
- high muscle mass or creatine supplement use.
If creatinine has suddenly increased compared with previous results, clinicians will usually consider acute kidney injury, dehydration, medicine effects or obstruction. If creatinine has been stable over months or years, that points more towards a long-term baseline.
Low creatinine
Low creatinine is usually related to lower muscle mass, pregnancy or reduced protein intake. It is not usually dangerous by itself, but it can make kidney function estimates less straightforward in frail or very low-muscle-mass patients.
eGFR result explained
eGFR stands for estimated glomerular filtration rate. It is calculated from creatinine, age and sex, and estimates how much blood your kidneys filter each minute. Many UK laboratories now report eGFR alongside creatinine.
A higher eGFR usually means better kidney filtration. However, eGFR is an estimate, not a direct measurement, and it is less accurate in some situations, including pregnancy, acute illness, very high or low muscle mass, bodybuilders, amputees and people taking creatine supplements.
How to understand eGFR bands
| eGFR result | Broad meaning |
|---|---|
| 90 or above | Usually normal kidney filtration, unless there are other signs of kidney disease such as protein in urine. |
| 60–89 | Mildly reduced. May be normal for age in some people, but needs context. |
| 45–59 | Mild to moderate reduction. Often repeated and checked with urine ACR. |
| 30–44 | Moderate to severe reduction. Usually needs regular monitoring and risk reduction. |
| 15–29 | Severe reduction. Specialist input is often needed. |
| Below 15 | Very severe reduction. Requires urgent or specialist kidney care depending on context. |
The UK Kidney Association explains that chronic kidney disease classification depends not only on eGFR, but also on the amount of protein or albumin in the urine. Their CKD staging guide shows why eGFR and urine albumin are interpreted together.
This is why a U&E blood test is often followed by a urine ACR test if kidney disease is suspected. NICE guidance on chronic kidney disease assessment and management also uses eGFR and albuminuria to guide monitoring and care.
Chloride result explained
Chloride is an electrolyte that helps maintain fluid balance and acid-base balance. It often moves in relation to sodium and bicarbonate. Chloride is not always the headline result on a U&E report, but it can be useful when doctors are looking at dehydration, vomiting, diarrhoea, kidney problems or acid-base disturbances.
High chloride
High chloride may be seen with dehydration, some types of metabolic acidosis, diarrhoea, kidney tubular problems or after receiving certain intravenous fluids. It is usually interpreted alongside bicarbonate and the overall clinical picture.
Low chloride
Low chloride may occur with prolonged vomiting, some diuretics, metabolic alkalosis or fluid imbalance. Again, it is rarely interpreted alone.
Bicarbonate result explained
Bicarbonate helps buffer acids in the body. It gives doctors clues about acid-base balance. In many outpatient blood tests it is only mildly abnormal, but in unwell patients it can be very important.
Low bicarbonate
Low bicarbonate may suggest metabolic acidosis. Possible causes include kidney disease, severe diarrhoea, diabetic ketoacidosis, lactic acidosis, sepsis, some toxins or certain medicines. If low bicarbonate is found in someone who is acutely unwell, it may require urgent assessment.
High bicarbonate
High bicarbonate may be seen with prolonged vomiting, some diuretics, dehydration, chronic lung disease compensation or metabolic alkalosis. It needs context and is usually assessed alongside chloride, potassium and symptoms.
What patterns do doctors look for in U&E results?
Individual markers matter, but the pattern often matters more. A single abnormal number does not always tell the full story.
Pattern 1: High urea and high creatinine
This may suggest reduced kidney filtration. The key question is whether it is new or longstanding. A sudden rise may point towards acute kidney injury, dehydration, severe illness, urinary blockage or a medicine effect. A stable long-term rise may suggest chronic kidney disease.
Pattern 2: High urea with less change in creatinine
This pattern can occur with dehydration, high protein intake, catabolic illness or gastrointestinal bleeding. Doctors will consider symptoms such as thirst, reduced urine output, vomiting, diarrhoea, black stools or feeling faint.
Pattern 3: Low sodium with normal kidney function
This may happen with excess water retention, certain medicines, hormonal problems, heart failure, liver disease, or SIADH. Symptoms and severity guide urgency.
Pattern 4: High potassium with reduced eGFR
This combination is important because the kidneys remove potassium. Doctors will review kidney function, medicines, supplements, salt substitutes and whether the blood sample could be falsely high.
Pattern 5: Abnormal potassium but normal kidney function
This can happen with sample problems, diet or supplements, medicines, hormone problems, vomiting, diarrhoea or shifts of potassium between the blood and cells. Repeat testing is often needed, especially if the result does not fit the clinical picture.
Pattern 6: Reduced eGFR with protein or blood in urine
This is more concerning than reduced eGFR alone. If kidney disease is suspected, a urine ACR test, blood pressure check and review of diabetes or cardiovascular risk are often part of the next step. You can read more in our guide to urine test results.
When are abnormal U&E results urgent?
Many abnormal U&E results can be reviewed routinely, especially if the change is mild and you feel well. However, some results need urgent medical advice.
Seek urgent medical help now, or follow urgent instructions from your GP, laboratory or out-of-hours service, if you have abnormal U&Es with:
- chest pain, severe breathlessness or collapse;
- fainting, severe palpitations or a very irregular heartbeat;
- new confusion, severe drowsiness or seizures;
- very reduced urine output or inability to pass urine;
- severe dehydration, persistent vomiting or severe diarrhoea;
- known kidney disease and a sudden deterioration in results;
- a very high potassium result, especially around 6.5 mmol/L or above;
- rapidly worsening creatinine or eGFR compared with previous results.
If you have symptoms such as chest pain, severe dizziness, fainting or severe dehydration, do not wait for a routine appointment.
Can medicines affect U&E results?
Yes. Medicines are one of the most common reasons U&Es are checked. Some medicines can affect kidney function, sodium, potassium or hydration status. This does not mean they are “bad” medicines. Many are protective and important, but they need monitoring.
Medicines that may affect U&E results include:
- ACE inhibitors, such as ramipril, lisinopril or enalapril;
- ARBs, such as losartan, candesartan or valsartan;
- diuretics, such as furosemide, bendroflumethiazide or indapamide;
- spironolactone, eplerenone or amiloride;
- NSAIDs, such as ibuprofen, naproxen or diclofenac;
- lithium;
- trimethoprim and some other antibiotics;
- potassium supplements or potassium-containing salt substitutes.
Do not stop prescribed medicines without speaking to a clinician, unless you have been given specific sick-day guidance or urgent instructions. If your kidney function or potassium has changed, your GP or specialist may temporarily pause, reduce or review certain medicines depending on the situation.
Can dehydration affect U&E results?
Yes. Dehydration can affect several U&E markers. It may raise urea, sometimes raise creatinine, and can disturb sodium and potassium. Dehydration can happen after vomiting, diarrhoea, fever, heat exposure, poor fluid intake, excessive sweating or some diuretics.
In mild dehydration, drinking fluids and repeating the blood test may be enough, if advised by a clinician. In more severe dehydration, especially with confusion, collapse, very low urine output, severe weakness or ongoing vomiting, urgent medical care may be needed.
For related advice, see our guide to dehydration symptoms in adults and children.
Can diet affect U&E results?
Diet can influence some U&E markers, but it is rarely the only explanation for a significant abnormality.
- A high-protein diet can sometimes increase urea.
- Creatine supplements and high muscle mass can affect creatinine.
- Potassium-containing salt substitutes can raise potassium, especially in people with kidney disease or those taking certain blood pressure or heart medicines.
- Very low food intake, vomiting or diarrhoea can contribute to electrolyte changes.
If you have been told your potassium is high, do not start a strict low-potassium diet without advice. Potassium restriction is not appropriate for everyone and can be nutritionally unhelpful if done incorrectly. The priority is to identify the cause, review medicines and decide whether repeat testing or urgent treatment is needed.
Can exercise affect U&E results?
Recent intense exercise can sometimes affect creatinine and potassium, particularly if it caused muscle breakdown, dehydration or supplement use. In most people, ordinary exercise does not cause major U&E abnormalities.
If you had a blood test soon after a very intense workout, endurance event, heat exposure or muscle injury, tell the clinician interpreting your results. They may consider repeating the test when you are well hydrated and rested.
What happens after abnormal U&E results?
The next step depends on which result is abnormal, how abnormal it is, whether it is new, and whether you have symptoms.
Your clinician may recommend:
- repeating the blood test to confirm the result;
- checking previous U&E results to look for a trend;
- reviewing your medicines, supplements and salt substitutes;
- checking blood pressure;
- doing a urine dipstick or urine ACR test;
- checking diabetes markers such as HbA1c;
- arranging further blood tests, such as full blood count, liver function, calcium, phosphate or inflammatory markers;
- arranging an ultrasound if obstruction, kidney structure problems or urinary retention are suspected;
- referring to a kidney specialist if results are significantly abnormal or worsening.
If your abnormal result came from a private test, it is still important to make sure the result is clinically followed up. Our guide to what to do after abnormal private blood test results explains how to decide whether to contact the private provider, your GP, NHS 111 or urgent care.
How often should U&Es be checked?
There is no single answer. Some people only need U&Es occasionally as part of routine care. Others need regular monitoring because of kidney disease, high blood pressure, diabetes, heart failure or medicines that can affect kidney function or potassium.
U&Es are commonly checked:
- before and after starting certain blood pressure or heart medicines;
- after dose changes to ACE inhibitors, ARBs, diuretics or spironolactone;
- during monitoring for chronic kidney disease;
- during diabetes or high blood pressure reviews;
- before some scans, operations or treatments;
- during acute illness if dehydration or kidney injury is possible.
If you have high blood pressure, kidney disease or cardiovascular risk factors, you may also find these guides helpful: High Blood Pressure: Symptoms, Causes and Treatment, Home Blood Pressure Monitoring and Cardiovascular Risk Explained.
Can U&E results diagnose chronic kidney disease?
U&E results can help detect reduced kidney function, but chronic kidney disease is not usually diagnosed from one blood test alone. In general, chronic kidney disease means there is evidence of kidney abnormality for at least three months. This may involve reduced eGFR, protein in the urine, blood in the urine, structural abnormalities or other kidney-related findings.
A single low eGFR may be caused by dehydration, acute illness, medicines or a temporary kidney injury. That is why repeat testing and urine testing are often important.
If eGFR is below 60, your clinician will usually look at previous results and may arrange a repeat test. If eGFR remains reduced, urine ACR and blood pressure are important for risk assessment.
Can U&E results be wrong?
Sometimes a result can be misleading. This is especially true for potassium. A potassium result may be falsely high if the blood sample was difficult to take, delayed in reaching the lab, shaken, affected by blood cell breakdown, or contaminated by another tube type. This is sometimes called pseudohyperkalaemia.
Creatinine and eGFR can also be misleading in people with unusual muscle mass, recent intense exercise, creatine use, pregnancy or acute illness.
This is why repeat testing is common when a result is unexpected or does not fit how you feel. However, do not assume a result is wrong if it is significantly abnormal. Follow the advice given by the laboratory, GP or clinician.
How to read your U&E report sensibly
When you receive your result, try not to focus only on whether a number is just outside the reference range. Instead, ask these questions:
- Which marker is abnormal? Sodium, potassium, urea, creatinine and eGFR mean different things.
- How abnormal is it? A borderline change is different from a major abnormality.
- Is it new? Comparing with previous results is very useful.
- Do you have symptoms? Symptoms can change the urgency.
- Were you unwell or dehydrated? Recent illness can affect results.
- Are you taking medicines that affect kidney function or potassium? This is one of the commonest explanations.
- Was urine tested too? eGFR plus urine ACR gives a better kidney-risk picture than eGFR alone.
If you are unsure what your result means, ask the clinician or provider who arranged the test. If the result is significantly abnormal or you feel unwell, do not wait for a routine review.
FAQ: U&E blood test results
What is a U&E blood test?
A U&E blood test checks urea and electrolytes. It usually includes sodium, potassium, urea, creatinine and often eGFR. It is commonly used to assess kidney function, hydration and electrolyte balance.
Is U&E the same as a kidney function test?
Often, yes. In everyday UK practice, U&E is commonly used as a kidney function blood test. However, a full kidney assessment may also include urine ACR, blood pressure, diabetes checks, medication review and sometimes imaging.
What does a high urea result mean?
High urea can occur with dehydration, reduced kidney function, acute illness, high protein intake or gastrointestinal bleeding. It is usually interpreted alongside creatinine, eGFR, symptoms and previous results.
What does a high creatinine result mean?
High creatinine can suggest reduced kidney filtration, but it can also be influenced by muscle mass, dehydration, recent intense exercise, creatine supplements and some medicines. A sudden rise is often more concerning than a stable long-term result.
What eGFR result is concerning?
An eGFR below 60 may need repeat testing and urine ACR, especially if it persists for three months or more. Lower eGFR levels, rapidly falling eGFR, protein in the urine or symptoms may need more urgent assessment.
What potassium level is dangerous?
The level of concern depends on the person, symptoms, ECG findings and how quickly potassium has changed. Markedly high potassium, especially around 6.5 mmol/L or above, is usually treated as urgent. Always follow the advice of your GP, laboratory, out-of-hours service or hospital team.
Can dehydration cause abnormal U&E results?
Yes. Dehydration can raise urea, sometimes affect creatinine, and disturb sodium or potassium. Vomiting, diarrhoea, fever, heat exposure and poor fluid intake are common triggers.
Can medicines affect U&E results?
Yes. ACE inhibitors, ARBs, diuretics, spironolactone, NSAIDs, lithium, trimethoprim and potassium supplements can affect kidney function or electrolyte levels. Do not stop prescribed medicines without medical advice unless you have been given specific instructions.
Do I need to fast before a U&E blood test?
Usually not. U&Es normally do not require fasting. However, if your blood test includes other markers such as glucose or lipids, you may be given specific instructions.
Can a private blood test diagnose kidney disease?
A private blood test can identify abnormal kidney markers, but diagnosis and follow-up depend on context, repeat results, urine testing and clinical assessment. If your private U&E result is abnormal, make sure it is reviewed by an appropriate clinician.
Should I drink lots of water before repeating U&Es?
You should be normally hydrated, but do not overdrink. Excessive water intake can itself affect sodium levels. If you have heart failure, kidney disease or fluid restrictions, follow your clinician’s advice.
Why would my potassium be high if my kidneys are normal?
Possible reasons include sample problems, certain medicines, supplements, salt substitutes, hormonal issues, acute illness or shifts of potassium between cells and blood. Unexpected high potassium is often repeated, but significant results still need prompt medical advice.
Can U&E results show liver disease?
U&Es are mainly used for kidney function and electrolytes. Urea can be affected by liver function in some situations, but liver disease is usually assessed with liver blood tests. See our guide to liver function test results.
Can U&E results explain tiredness?
Sometimes. Kidney dysfunction, sodium abnormalities, potassium abnormalities or dehydration can contribute to tiredness. However, tiredness has many possible causes, including anaemia, thyroid problems, vitamin deficiencies, sleep problems, stress and infection. See Fatigue: Why Am I Always Tired?.
What should I do if my U&E result is abnormal?
If the abnormality is mild and you feel well, contact the clinician or service that arranged the test for interpretation. If the result is significantly abnormal, potassium is very high, kidney function has suddenly worsened, or you have symptoms such as chest pain, fainting, confusion, severe dehydration or reduced urine output, seek urgent medical advice.
