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What are kidney biomarkers and what can they tell me about my health?

All HOMED-IQ content is reviewed by medical specialists

Our kidneys are vital organs that play an important role in our bodies. The main function of the kidneys is to filter the body’s blood, removing waste products and water to create urine. The kidneys also regulate fluid levels in the body and produce hormones that control blood pressure, as well as regulate electrolyte balance. Therefore, it is important to ensure that our kidneys are healthy and free of disease or dysfunction. The health of our kidneys can be checked by looking at kidney biomarkers. But what exactly are kidney biomarkers, how do you measure them, and which biomarker levels are normal? In this article, we would like to examine these questions in more detail.

What do the kidneys do?

Around 1,800 liters of blood flow through the kidneys every day. About ten percent of this (~180 liters) is filtered out as primary urine and then concentrated into approximately two liters of urine. As such, both blood and urine play a vital role in diagnosing kidney problems. If a kidney disorder is suspected, a blood and urine sample is usually taken and tested.

When is a kidney test performed?

Kidney tests are generally performed when there is a suspicion of problems with the kidneys, or to periodically check kidney function if an individual has a known disease that impacts the kidneys, such as diabetes. 

Typical symptoms of kidney problems are dull lower back and flank pain, a sensitivity to cold, joint pain, and fatigue. However, early-stage kidney diseases often cause little to no symptoms. Because of this, testing is a useful tool in detecting kidney problems before irreversible damage occurs. 

What are kidney biomarkers?

Kidney biomarkers are molecules that appear in the blood or urine that show how well the kidneys are working and can be measured with a laboratory test. There are two ways to determine the value of kidney biomarkers; with a urine test, and with a blood test. However, there is not just one biomarker that indicates the health of the kidneys. Read on to learn about the primary biomarkers for checking kidney function and health.

Creatinine and eGFR

You may have heard of creatine as a dietary supplement among athletes, but did you know that creatine is also important outside of weight training? Creatine is a protein that is stored in the muscles, where it is used for energy. While the body can produce small amounts of this protein, most creatine is obtained through diet. Approximately one to two percent of creatine is broken down by the body every day into creatinine, which is then filtered out and excreted via the kidneys as urine. Since the amount of creatinine that is excreted varies depending on the amount consumed, the creatinine level that can be detected in a test also varies. The process by which creatinine levels are detected in urine and blood is also known as creatinine clearance. Muscles have a direct influence on creatinine levels, which means that athletes and muscular people often have a creatinine level above the normal range. However, an increased creatinine value can also be an indication of kidney disease. A creatinine value that is lower than normal is generally no cause for concern.

Another value that can be determined with a creatinine test is the estimated glomerular filtration rate (eGFR). eGFR is a measure of how well your kidneys are working, and is calculated based on the amount of creatinine in your blood as well as other personal factors such as age and sex.  Healthy kidneys filter creatinine out of the blood as urine. If the kidneys are not working properly, creatinine levels will build up in the blood. It is important to mention that this value can vary depending on age, gender, body type, and race. Furthermore, the eGFR is often not meaningful for people who are severely overweight, pregnant, or very muscular.

Urea

Urea nitrogen is a waste product created when the body breaks down protein from the food we eat. This non-toxic urea is formed when the liver creates ammonia, which is released when protein is broken down. Ammonia then combines with other elements to create urea, which travels from the liver to the kidneys via the bloodstream. Urea is then excreted through the kidneys. If the kidneys are not healthy, they may have trouble removing urea nitrogen, causing levels in the blood to rise. Blood urea nitrogen (BUN) that is higher than normal can be an indicator of chronic kidney disease. However, increased levels can also be caused by dehydration, tissue damage (such as burns), or due to a high protein diet.

Albumin

Albumin is a protein produced by the liver that carries substances such as hormones, drugs, and enzymes throughout the body. Albumin also helps prevent fluid in the blood from leaking into body tissues. In well-functioning kidneys, only a small amount of albumin will leak into the urine. In case of damage to the kidneys, higher amounts of albumin will be found in the urine. This is especially seen in people with high blood pressure or diabetes.

Microalbumin (also called the albumin/creatinine ratio) is the ratio between the amount of albumin and the creatinine excreted in a portion of urine. Urinary microalbumin levels can be increased by certain medications, recent exercise, urinary tract infections, and blood in your urine. If your microalbumin levels are elevated, please consult your GP- they may ask you to repeat the test.

What kidney biomarker values are normal?

Below you will find an overview of normal kidney biomarker values. Variation from these values can be normal depending on certain personal factors like age, gender, or lifestyles that naturally increase certain markers. 

A safe and easy way to check three important kidney biomarkers is with Homed-IQ’s Liver and Kidney Function Test. With this test, users can check their creatinine, eGFR, and microalbumin levels, as well as important liver biomarkers ALT, AST, GammaGT, bilirubin, and alkaline phosphatase. This self-test involves taking a blood and urine sample from home, followed by submitting the sample to a certified laboratory for analysis. You will receive a complete laboratory report that can be brought to your GP for further investigation if needed.

Kidney valuesMeasured inValue
CreatinineBlood59,2 to 103,4 μmol/l
eGFRBlood> 60 ml/min
Urea NitrogenBlood6 to 24 mg/dL
MicroalbuminUrine< 20 mg/L

What does it mean when kidney biomarkers are outside the normal range?

Kidney biomarkers that fall outside the normal range can indicate kidney damage or disease. However, other illnesses and personal factors can also impact kidney biomarkers. If your test results are abnormal, please take them to your GP for further investigation. You may need additional testing or to repeat a test to see if the result is still abnormal. Furthermore, if your test result is normal but you are still experiencing symptoms consistent with kidney dysfunction, visit your GP to check in. 

Biomarkers that are too low

Low kidney biomarkers are usually less significant than overly high values, but can still indicate potential problems in the body. Low creatinine levels, for example, can indicate a problem with the muscles or liver, but could also be due to something less serious, such as reduced muscle mass in older adults, or pregnancy. A low blood urea nitrogen value can be the result of a poor diet, malnutrition, overhydration, pregnancy, or liver damage. Microalbumin values that are below 20 mg/L are considered to be within the normal range. 

A low eGFR indicates that the kidneys may not be working as well as they should, but can also decrease with age. As with all test results, kidney disease cannot be diagnosed if one biomarker is out of range. If you receive a test result that is outside the normal range, your doctor will investigate potential causes, order additional tests if needed, and make a formal diagnosis.

Biomarkers that are too high

Early-stage kidney damage or disease can cause elevated kidney biomarkers before symptoms occur. High amounts of creatinine and urea nitrogen in the blood indicate the kidneys are not clearing these substances properly, and may not be working correctly. High levels of microalbumin in the urine can be a sign of early-stage kidney disease or kidney failure. However, there are other factors that can affect microalbumin levels, such as vigorous exercise, which will need to be investigated by your doctor. Finally, a high eGFR value is no cause for concern and indicates the kidneys are functioning well..

What should you do if your kidney function test results are abnormal?

If your kidney biomarkers are outside the normal range, visit your GP to learn more about the potential causes, whether disease is present, and what the treatment options are. You may need certain medications, additional testing, or to follow up with a nephrologist (a kidney specialist). 

You should also be aware that smoking, unmanaged high blood pressure, and excessive consumption of certain medications like ibuprofen, naproxen, and aspirin can impact kidney health. Long-term use of painkillers, antibiotics and other medications lead to kidney damage. People who are already struggling with existing kidney problems should keep a careful record of their medication dosages and doses and consult their doctor to see if medications or dietary supplements should be avoided altogether. Furthermore, it is important to correctly manage your blood pressure and blood sugar (in diabetics) if you have a known history of kidney damage. Following a health diet, maintaining a healthy weight, and not smoking are also ways to protect your kidney health.

Bibliography

Door, R. (2021, August 12). Kidney Values: Measure of kidney function. Pharmacy magazine. Retrieved August 2, 2022, from https://www.apotheken-umschau.de/diagnose/laborwerte/nierenwerte-mass-fuer-die-nierenfunktion-741527.html

Görgen, J. (2020, December 7). Kidney values: normal values and meanings. practicaldoctor. Retrieved on August 2, 2022, from https://www.praktikalarzt.de/Investigations/Blood Analysis/nierenvalues/

Machetanz, L. & Rudolf-Müller, E. (2017, November 20). kidney values. NetDoctor. Retrieved on August 2, 2022, from https://www.netdoktor.de/laborwerte/nierenwerte/

Stephan, R.M.H. (2021, August 22). All kidney values in the blood count simply explained. grossesblutbild.de. Retrieved on August 2, 2022, from https://www.grossesblutbild.de/nierenwerte.html

About the Author

Lauren Dobischok

Lauren is a health scientist and science communicator living in the Netherlands. She has completed a Research Master in Health Sciences at Erasmus University Rotterdam’s Netherlands Institute for Health Sciences (NIHES) with a specialization in epidemiology, and a B.Sc. in Health Sciences at Simon Fraser University. With a background in public health, her goal is to create accurate scientific content that is easy to understand and enables people to make informed decisions. Within Homed-IQ, Lauren serves as Product Developer and Content Lead, working closely with medical doctors and medical device scientists on Homed-IQ’s new products and written communications.