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Understanding your kidney function results

An illustration showing blood going into your kidney, filtered blood coming out and wastes (urine) going to your bladder.The most common test to check how well your kidneys are working is a blood test called a kidney function or renal function test.

Doctors may check your kidney function before or after you start a medicine that can affect your kidneys or as part of a wellbeing check.

Your kidneys balance the salt and water content in your body and get rid of some waste products. They do this by acting like a filter system for your blood.

It's good to know what your blood results can tell you about your kidney health. If you've had a kidney function blood test, talk to your health professional who can explain what your results mean.

Terms used

Na: this is sodium, one of the salts in your blood that your kidneys help to control. Sodium helps your body create energy and keep the right balance of salt and water.

K: this is potassium, another one of the salts in your blood that your kidneys control. Potassium is important for your muscles and nerves to work properly.

Urea: this is a waste product that comes from protein. Your kidneys get rid of it through your urine.

Creat: this is creatinine, a waste product that comes from normal muscle activity. Your kidneys get rid of it through your urine.

eGFR: this stands for estimated glomerular filtration rate, a calculation that tells how much kidney function you have. When you look at your result, it's important to know that kidney function decreases with age even in people without kidney disease.

Normal results

If you have a copy of your test results, it will show your results and a normal range for each test. The normal ranges may vary depending on your gender and age group and whether you're pregnant or have any underlying health conditions. So, the normal ranges shown on your test results may not be exactly right for you. Discuss your results with your doctor or practice nurse if you're unsure.

High results

If your urea or creatinine levels are high, it can be a sign of kidney damage or dehydration (not enough fluid).

A high sodium level is usually a sign of dehydration.

A high potassium level could be a false reading due to a problem with the blood sample. It could also be a sign of kidney damage.

Low results

Low sodium could mean your blood has too much water in it, or it could be due to a medication you're taking.

Low potassium means your body has lost too much potassium through your urine or from vomiting and diarrhoea.

If your eGFR is low, your kidneys aren't filtering as well as they should do. This is a sign of kidney damage.

Next steps

If your blood results are too high or too low, talk to your doctor or nurse.

Talk to your health provider if you have more questions about your kidney function test or if want to know more about how you can help to look after your kidneys.

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Written by HealthInfo clinical advisers. Last reviewed March 2019. Last updated July 2021.

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