Summary

• Urea is a waste product.
• Your kidneys filter your blood, removing waste and water to make urine.
• Measuring urea levels in your blood can show how well your kidneys are working.

What is urea?

Urea is a waste product which is formed when your body breaks down protein. Proteins are built from molecules called amino acids. As amino acids are metabolised, they release ammonia and nitrogen which are highly toxic. It is important to remove nitrogen from your body, and to do this, your liver converts the ammonia and nitrogen it into urea, which is less toxic.

Your kidneys filter your blood, removing waste and water to make urine. The urine flows from your kidneys to your bladder to be disposed of. The urea, still containing nitrogen, travels from your liver to your kidneys through your bloodstream. Healthy kidneys filter urea and remove it from your blood.

Measuring urea levels in your blood can show how well your kidneys are working. A small amount of urea in your blood is normal. Healthy kidneys remove more than 90 per cent of the urea the body makes. If levels rise, it is possible that your kidneys are not working as well as they should.

Why get tested?

Urea levels rise with age and are slightly higher in men than women. They are affected by how much muscle mass you have and by the amount of protein in your diet.

You may be asked to have a urea test as part of a routine checkup, especially if you are at risk of kidney disease from another condition, such as diabetes or high blood pressure. But because urea levels can be affected by many factors, testing for kidney function is more often done by measuring levels of creatinine, another waste product that is filtered by your kidneys.

When urea testing is performed, a test for electrolytes and creatinine is usually ordered at the same time. This is called a U&E test. The U&E tests are performed together because they provide a comprehensive assessment of kidney function, fluid balance and electrolyte levels in your blood.

High urea levels

High urea levels suggest that your kidneys are not working as well as they should. This may be due to kidney disease but there are many other things that can affect urea levels such as:

• High protein diet
• Serious illness (such as sepsis, heart attack, or severe burns)
• Dehydration
• Intestinal bleeding
• Kidney obstruction or reduced flow (such as kidney stones or congestive heart failure)
• Drugs (such as steroids, and diuretics)

Low urea levels

Low urea levels are not common although they can be seen in a range of conditions, but other tests are generally used to diagnose or monitor these conditions. Possible reasons for low urea levels include:

• Pregnancy (especially in the final weeks)
• Liver failure
• Malnutrition
• Androgens (such as growth hormone and insulin treatment)
• Urea cycle disorders (genetic conditions that interfere with the way the body breaks down protein)

Dialysis: If you are having dialysis treatment, urea and creatinine testing will be used to make sure your kidneys are staying healthy. Dialysis is intended to remove about two thirds of urea in each dialysis episode, with levels rising between dialysis sessions.

Nutrition: urea can be used as a nutritional marker to monitor eating disorders or to estimate how much protein someone needs to include in their diet (such as someone who is seriously ill).

Other uses: Urea can also be used along with other tests to detect conditions such as liver disease or damage, congestive heart failure or urinary tract obstruction. If someone has a serious infection such as pneumonia, urea testing can help identify if they are at a greater risk of a poor outcome and be used to guide management.

Urea urine testing

Very occasionally, urea is measured in a urine sample. This can involve testing all the urine you pass over a 24-hour period, but it can also sometimes be measured as a single test.

Testing urine for urea is mainly used to check how much protein someone has taken in from their food and to estimate the protein intake in their diet. It is usually performed for severely ill people.

Having the test

Sample

Blood or urine (24-hour or single sample)

Preparation

Diet and medications can influence urea test results.

• Avoid high-protein meals before taking the test to help ensure accurate results.
• Certain medications, such as diuretics, corticosteroids and antibiotics can affect urea levels. It’s important to inform your doctor about any medications or supplements you’re taking before the test.

Your results

Reading your test report

Your doctor will consider your age, medical history, and other factors when interpreting your results.

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

Reference intervals

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• When compared against them your results may be flagged high or low if they sit outside this range.
• Many reference intervals vary between labs so only those that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.

Reference intervals for urea

Reference intervals for serum urea in adults are typically 3.0 - 10.0 mmol/L. There may be slight variations depending on age and gender.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods, medications or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

Get further trustworthy health information and advice from healthdirect.