Urea and Electrolytes

The Urea and Electrolytes (U&E) test checks the salts, minerals and waste products in your blood that show how well your kidneys are working and whether your body's fluid balance is where it should be. It suits anyone monitoring blood pressure medication, recovering from vomiting or diarrhoea, or wanting a general kidney health check. The profile costs £73.75 plus a £50 blood-draw fee, with results back in 1 day. Walk in or book online at 117a Harley Street, seven days a week.

Doctors commonly request a U&E profile when someone reports tiredness, swelling in the ankles, unusual thirst, or a change in how often they pass urine, since all of these can trace back to kidney function or salt balance.

It is also used to monitor people taking blood pressure tablets, diuretics or other medicines that can affect the kidneys or potassium levels, and to check recovery after a bout of vomiting or diarrhoea that may have caused dehydration.

Some people request it as a standalone check before travel, surgery or starting a new fitness or supplement regime, simply to confirm their kidneys and electrolytes are behaving as expected.

Fasting is not usually needed for a U&E test, so most people can have this blood draw at any time of day. If your doctor has given you specific instructions, such as timing the sample around a medication dose, follow those instead.

Sodium, potassium, chloride and bicarbonate results that sit outside the expected range can reflect dehydration, fluid overload, or the effect of certain medicines, while changes in urea and creatinine are the markers doctors lean on most to assess how well the kidneys are filtering waste.

A single set of results rarely tells the whole story. Your GP or one of our doctors will want to read the report alongside your symptoms, medical history and any medicines you take before drawing conclusions. Our guide to eGFR and kidney function results explains why one low eGFR is repeated before anything is concluded.

If your results fall outside the laboratory's reference range, or you develop symptoms such as persistent swelling, confusion or a marked change in urination, arrange to see a doctor promptly.

If you want these markers alongside a doctor's examination and a wider health assessment, compare the Full Body MOT health check.

Written by Mr Stephen Lingam. Reviewed by Dr Mohammad Bakhtiar (GMC 4694470) on 24/09/2026.

• Sodium: Shows whether the salt and water balance in your blood is where it should be.
• Potassium: Reflects how well your kidneys and cells are managing this mineral, which your nerves and muscles rely on.
• Chloride: Moves alongside sodium and helps keep your body's fluids and acid levels stable.
• Bicarbonate: Indicates the acid-base balance of your blood.
• Urea: A waste product cleared by the kidneys, so the level can point to how well they are filtering and how hydrated you are.
• Creatinine: A muscle waste product that gives a more precise read on kidney filtering than urea alone.

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