Kidney disease is common in the US. Official statistics from the CDC indicate that more than 1 in 7 adults has chronic kidney disease. However, up to 90% of those affected are unaware that they have chronic kidney disease. This is because kidney damage often causes no symptoms in the early stages. It’s not until later stages of the disease that people begin to experience serious health consequences.
Learning these facts may leave you wondering how to check kidney function. It’s entirely possible that your kidneys are not functioning well, but you don’t know this yet. Is there a blood test for kidney disease? How do you know if you have normal kidney function levels?
How to Test for Kidney Function
There are a few different tests that can be used to measure how well the kidneys are working. These can be known as kidney function tests or renal function tests – both terms mean the same thing. The specific tests used may differ depending on a person’s medical situation.
- A blood test is used to measure creatinine, which is a waste product that’s normally filtered out by the kidneys.
- A blood test may also be used to measure blood urea nitrogen (BUN), another waste product that the kidneys normally remove. The ratio between BUN and creatinine can be used to distinguish between different types of kidney disease.
- Urine tests may also be used to evaluate kidney function. These may look for creatinine in the urine, and also a protein called albumin. Albumin is a protein in the blood that the kidneys normally don’t allow to pass through; if it’s present in the urine, this can indicate kidney dysfunction. The ratio of albumin to creatinine can be useful in evaluating kidney disease.
- The urine tests may also look for blood in the urine, which can be an indicator of certain types of kidney diseases (including infections and kidney stones). It can also look for bacteria and proteins in the urine.
There are various types of urine tests that may be used. Blood, protein, and bacteria are often tested for in a single urine sample. Creatinine and albumin may also be evaluated in a single urine sample, but in order to get a more accurate determination of the levels of these substances in the urine, a 24-hour urine sample may be used. Because these levels can vary according to your activity level, diet, and other factors, a 24-hour urine collection is a more accurate way to test the average levels of these substances in your urine. Taking a 24-hour urine test requires you to collect all of your urine over a 24-hour period.
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What’s the link between creatinine levels and kidney function?
Levels of creatinine are the most common blood test for kidney function. Creatinine is created by the breakdown of proteins in the muscles. This process occurs on a daily basis, as proteins in the muscle break down and are replaced regularly.
The kidneys normally filter creatinine out of the blood. In people with a lower level of kidney function, the level of creatinine in the blood will rise, as the kidneys are not filtering it out. The measured level of creatinine is used to calculate the estimated glomerular filtration rate (eGFR), which estimates how quickly the kidneys are filtering the blood.
Although there is a link between creatinine levels and kidney disease, there are other conditions that can also increase creatinine. For example, anything that increases the breakdown of protein in the muscle will also lead to an increase in creatinine. Very athletic people sometimes have higher levels of creatinine, both because they have more muscle mass and because their frequent workouts increase the breakdown of protein in their muscles. Even if they have normal kidney function, their kidney function blood test may look as though their kidney function is impaired, because of the higher creatinine level. This is why an increased creatinine level needs to be evaluated in light of a patient’s specific situation.
Should you check kidney function regularly?
Certain groups of people are at higher risk for kidney disease. It’s recommended that people who have the following conditions get a blood test to check kidneys at least once a year:
- High blood pressure
- Heart disease
- History of conditions that can damage the kidneys, such as kidney infections or kidney stones
- Family history of kidney disease
You can go to a laboratory to give the samples for your testing, or you may choose to order a home testing kit. This allows you to take your samples in the privacy of your own home, and mail them to a laboratory. You then get your results online. If you have any abnormal kidney blood tests, then you’ll have the opportunity to discuss your results with a medical professional via telemedicine, in order to make a plan for what to do next.
People who currently have symptoms that could indicate kidney disease (such as fatigue, trouble sleeping, swelling of the hands and feet, or frequent need to urinate) should visit their doctor to discuss these. Your doctor will evaluate your symptoms and consider the various possible causes. Depending on this evaluation, they may order a urine and/or blood test to check kidneys, and might also order various other tests in order to arrive at the right diagnosis. The symptoms of many different conditions can overlap, and it can sometimes be tricky to tell different diseases apart, so it’s a good idea to get professional guidance rather than trying to diagnose yourself.
Chronic Kidney Disease in the United States, 2021. Centers for Disease Control and Prevention. https://www.cdc.gov/kidneydisease/publications-resources/ckd-national-facts.html. Accessed 21 June 2022.
Chronic kidney disease. National Health Service. https://www.nhs.uk/conditions/kidney-disease/diagnosis/. Accessed 21 June 2022.
Kidney Function Tests. Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/21659-kidney-function-tests. Accessed 21 June 2022.
Testing and Treatment: Find it Early, Treat it Early. Centers for Disease Control and Prevention. https://www.cdc.gov/kidneydisease/publications-resources/annual-report/ckd-testing-treatment.html. Accessed 21 June 2022.