What we measure
This test measures three markers of health that indicate whether the kidneys are working properly. The kidneys filter out waste from the blood and then transform it into urine so it can be passed out of the body. The below markers can tell us how well that process is working, which can signal whether the kidneys are functioning normally.
Creatinine
Creatinine is a waste product made by your muscles as part of their regular activity. Your kidneys usually filter creatinine out, so if its levels are high this can be a sign of kidney disease.
Estimated glomerular filtration rate (eGFR)
This is a calculation that estimates how much waste your kidneys can filter per minute. It takes into account your creatinine levels, age, the sex you were assigned at birth, and ethnicity, and can tell us whether your kidneys are functioning normally.

This test can help indicate if you’ve got kidney disease.
Your kidneys’ main job is to remove toxins and waste from your blood, and to make sure these are passed out of your body as urine. They also make sure your body has the amount of water it needs to function and release a number of essential hormones.
When your kidneys can’t do these jobs properly, waste products (like urea and creatinine) and excess fluid can accumulate in the body and cause health problems.
A blood test is the main way to investigate whether you’ve got kidney disease. You may need one if you’ve got symptoms of kidney disease, including fatigue, decreased appetite, weight loss, shortness of breath, and blood in your urine.
In the early stages, kidney disease doesn’t usually have any symptoms, so a test may be recommended if you’re at a high risk of it developing. People with diabetes, high blood pressure, or a family history of kidney disease fall into this camp.
Your results:
what to expect
Your test results will tell you how much urea and creatinine are in your blood, plus a calculation of your eGFR, and whether each of these readings fall within normal ranges.
If your urea and creatinine levels are higher than normal, and/or if your eGFR is lower than normal, this can indicate that your kidneys are not functioning properly.
eGFR results are given in stages from 1-5, with stage 1 being normal function and stage 5 being the most severe level of kidney damage.
Abnormal levels of urea and creatinine can also be caused by reasons other than the kidneys. So, if you get a high result for either of these, it’s best to speak with a doctor who will be able to investigate further.

Need help? Speak with an expert
Don’t quite understand your results or simply want to see a doctor? We’ve got you sorted.
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Just fill out an online form and find a time that’s convenient.
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Need to get your medication? Our GPs can write private prescriptions.
Tell the GP what the problem is during your consultation and they’ll take it from there. Prescriptions can be picked up at your local pharmacy.
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FAQs
Blood tests are the main way to test for kidney disease. Your eGFR is considered the most accurate way to identify changes in kidney function, which is calculated using the amount of creatinine in your blood.
Depending on your situation, your doctor might suggest other tests to assess your kidney health, such as an ultrasound scan or urine test.
If you think you have kidney stones, your doctor may suggest a blood or urine test. If you have passed any stones, they may want to examine those as well.
A kidney function test can indicate kidney stones, as they can cause eGFR to drop. However, your test result can’t diagnose kidney stones on its own.
If you have abnormal results, your doctor may wish to run further tests that are specifically focused on identifying kidney stones (for example that look for levels of minerals in the blood that can cause stones to form) rather than kidney health more generally.
Yes, a blood test can evaluate whether your kidney is working as it should be. Your eGFR is considered the most accurate measure of this.
Blood test results are not a diagnosis in themselves but they are often an important step towards getting one. Your results can help doctors decide whether and how they should investigate further, and can be used alongside other findings to diagnose disease.
Nope, fasting isn’t required for this test, but it’s recommended that you avoid meals high in protein as this can increase levels of creatinine and urea.
Yes, it can. Staying hydrated is super important for kidney health. If you don’t drink enough water, the kidneys reabsorb whatever is in your system rather than passing it out as urine. This can cause waste products to build up inside the body, which can increase levels of urea.
Alcohol is a diuretic, which means that it dehydrates you. Being dehydrated can affect your results.
You can reduce the risk of dehydration by drinking within the recommended limits, which is 14 units of alcohol per week for an adult in the UK, and by drinking glasses of water in between alcoholic beverages.
