Urea and Electrolytes (U&E): What the Test Measures

1. What does U&E stand for?

U&E stands for urea and electrolytes. It is a routine panel of blood tests that checks two things at once. First, how well your kidneys are filtering waste. Second, whether the salts that keep your body running are in balance.

The urea line is the one people query most. How near the top of the range it sits depends on your age, which urea levels by age sets out decade by decade.

Electrolytes are the salts and minerals in your blood. The NHS defines them simply.

“Electrolytes are salts and minerals, such as sodium, potassium, chloride and bicarbonate, which are found in the blood.”

— NHS, Electrolyte test

You may also see it called U&Es or a renal profile. Same panel. It is one of the checks in our full kidney function test guide.

2. What does the U&E test measure?

A standard U&E reports four core markers, and many labs add a calculated eGFR. Here is what each one is. The ranges are in the table below.

• Sodium. The main salt in your blood. It controls fluid balance and helps nerves and muscles work.
• Potassium. Vital for muscle and heart rhythm. Both very high and very low levels matter.
• Urea. A waste product made when your liver breaks down protein. Your kidneys clear it. It is swayed by hydration and diet, as is the total protein figure on the same report, which is why a urea under the range usually says more about your diet than your kidneys.
• Creatinine. A waste product from normal muscle use, cleared by the kidneys. It is the steadier kidney marker.
• eGFR. Estimated glomerular filtration rate. Not measured directly, but calculated from your creatinine, age and sex. It estimates how fast your kidneys filter. a reading of 84, 78 or 71 reads differently at 70 than at 30.

Holding the printout? Our guide to U&E results explained reads the numbers one at a time. For creatinine on its own, see the creatinine blood test guide and the deeper kidney function test guide.

3. What is a normal U&E result?

Here are the ranges UK labs commonly print. Your own report is the one that counts, because labs calibrate differently.

The NHS puts the eGFR line plainly.

“Healthy kidneys should be able to filter more than 90ml/min. You may have CKD if your rate is lower than this.”

— NHS, Chronic kidney disease: Diagnosis

One reading just outside a range is common and often means little. A repeat test is the usual next step, not a verdict.

4. What does a high or low U&E result mean?

Note which marker is flagged. Urea moving alone is a different story from urea and creatinine moving together.

• High urea. Usually water, not kidneys. Being short of fluid concentrates the blood. Lots of protein, and bleeding in the gut, also raise it. See high urea levels.
• Low urea. Often a low protein diet, pregnancy, or drinking a lot of water. Rarely a worry on its own.
• High creatinine. Can mean slower filtering. It also rises with muscle, hard training and creatine, so a lifter can read high and be fine.
• Low creatinine. Common with low muscle mass and in later pregnancy. See low creatinine levels.
• eGFR under 90. Filtering slows with age anyway. What counts is whether it keeps falling, and whether it stays under 60 on a repeat.
• Sodium or potassium off. These shift fast with medicines and illness. Your GP handles them, and a very high or very low potassium is urgent.

The NHS says: “The main test for kidney disease is a blood test. The test measures the levels of a waste product called creatinine in your blood.” That is why creatinine, and the eGFR worked out from it, carry more weight here than urea.

5. Why does my GP order a U&E?

A U&E is a broad check, not a test for one disease. Common reasons:

• Kidney health. Especially with diabetes or high blood pressure, which strain the kidneys over time.
• Medication checks. The NHS notes your levels may be checked on diuretics or ACE inhibitors, because they change body salts.
• Symptoms. Tiredness, feeling unwell, swollen ankles or dehydration can all prompt a U&E.
• A routine check. It is standard in many general health screens.

Kidney checks matter because early problems are silent. You can lose a lot of function before you feel anything.

“There are usually no symptoms of kidney disease in the early stages.”

— NHS, Chronic kidney disease

That is why a number tracked over time is useful. If a result looks off, our guide to reading blood test results explains the next steps.

6. How to check your kidney markers at home

A hospital U&E includes sodium and potassium, which shift quickly and are best monitored by your GP. A home finger-prick test focuses on the steadier filtration markers you can track over months.

Helvy’s Thyroid & Vital Organs panel (£159) measures urea, creatinine and eGFR, read alongside your thyroid and liver markers. The General Energy & Wellness panel (£149) also includes urea and creatinine. If your urea is the figure that came back flagged, our guide to normal urea levels explains why hydration and protein move it before your kidneys do.

To find the panel that fits what you want to check, the build-my-test tool matches you to the right markers. Results take about five working days, from UKAS-accredited UK laboratories. Weighing up a potassium supplement or a lithium orotate supplement? Your kidney markers are the thing to know first.

Frequently asked questions

Related guides