Kidney function tests are simple procedures that use either blood or urine to help identify kidney problems. There are a few types of kidney function tests, which investigate various aspects of kidney function.
A kidney function test may check how well the kidneys filter waste products. Another type of test may check whether the kidneys are leaking protein into the urine.
A doctor who thinks a person may have a kidney problem may order a kidney function test, but testing on a regular basis can be helpful for all adults.
According to the National Kidney Foundation, about 1 in 3 adults in the United States are at risk of kidney disease, and many people with early forms of the disease have no symptoms. Early diagnosis and treatment are important to effectively manage the disease and help
In addition to blood and urine tests, a doctor might order imaging tests to look at the kidneys.
In this article, we’ll talk about the various kidney function tests and what doctors can determine with their results.
Kidney function tests use either blood or urine to measure different aspects of kidney function.
Often, doctors will order more than one test at a time to get a broader picture of overall kidney function.
The kidneys play an essential role in keeping the body healthy. Their main job is to filter waste materials from the blood and send them out of the body in the urine.
Kidney damage can prevent the kidneys from properly filtering waste, and waste that remains in the body can cause dangerous symptoms.
Regular testing can help doctors identify kidney disease in very early stages and may make it possible to
Doctors may also order other tests, such as imaging scans or a biopsy, to get more information about the kidneys.
Urine tests may require either a small urine sample or all the urine a person produces in a 24-hour period.
Urinalysis
Urinalysis is a broad urine test that helps doctors identify underlying issues or determine which test to use next. Urinalysis may help identify many undesirable particles in the urine, including:
- blood
- minerals
- pus
- bacteria
- sugar
- protein
If the test comes back positive for one or more of these particles, it may indicate an underlying issue, such as:
- kidney or bladder infections
- kidney disease
- kidney stones
- diabetes
Microalbuminuria and urine albumin-to-creatinine ratio (uACR) tests
These two tests require a small urine sample. They both help identify levels of albumin in the urine.
Albumin is an important protein in the blood. If there is too much protein, it’s a sign that the kidneys are unable to filter correctly.
A uACR test result of 30 milligrams per gram (mg/g) or higher indicates too much albumin in the urine.
Microalbuminuria is a condition in which there is a tiny bit more albumin in the urine than there should be. Identifying microalbuminuria requires a much more sensitive test, which can detect even tiny amounts of the protein in the urine.
People who are at higher risk of kidney disease may need to take a microalbuminuria test even if other urine protein tests come back negative.
Creatinine clearance test
A creatinine clearance test requires both blood and urine. It involves
Creatinine is a waste product in the body that occurs naturally as a result of daily use of the muscles.
Doctors compare the amount of creatinine in the urine sample to the levels of creatinine in the blood. This comparison shows how much waste the kidneys are filtering out, which may be an indicator of overall kidney health.
For blood tests, a healthcare professional will insert a needle into a person’s arm to draw a small sample of blood. The person may need to fast beforehand or have the test first thing in the morning.
Serum creatinine test
Serum creatinine levels that are too high may be a sign that the kidneys are having trouble doing their job. Doctors will also order a serum creatinine test as part of the creatinine clearance test.
According to the National Kidney Foundation, serum creatinine levels can change depending on a person’s age, sex, body size, and other factors. A lower number is better. High numbers can be a sign of chronic kidney disease or kidney injury.
Glomerular filtration rate
Doctors may also calculate a person’s glomerular filtration rate (GFR) and use it to confirm their diagnosis or order more tests to check their results.
The GFR test takes the results of a serum creatinine test and adjusts them for other factors, such as age and sex. The typical GFR value is 90 or above. A GFR value of less than 90 can be a sign of kidney problems.
Blood urea nitrogen test
The blood urea nitrogen (BUN) test checks for urea nitrogen, a waste product, in the blood.
Urea nitrogen occurs as proteins from food break down, and elevated levels may be a sign that the kidneys are not effectively filtering these waste products.
BUN levels can change as a result of many factors besides kidney disease. Dehydration, burns, a recent heart attack, and certain medications can all increase BUN levels. Malnutrition, liver disease, and a lack of dietary protein can lead to abnormally low BUN levels. A person’s sex and age also affect the results.
Doctors typically compare these results to the results of a creatinine test to better understand how well the kidneys are filtering this waste.
Imaging tests may help doctors identify physical changes such as swelling or hydronephrosis, injuries, or kidney stones.
Ultrasounds
Ultrasound scans use sound waves to create real-time images of the inside of the body. Doctors may order an ultrasound to look for changes in the shape or position of the kidneys or to identify renal cysts.
CT scans
A CT scan uses a series of X-ray images to create a more in-depth, 3D picture of the kidneys. It may help doctors identify any structural changes in a kidney and see any potential tumors.
Sometimes a CT scan requires an injection of dye, which can be problematic for people who may have kidney disease.
MRI scans
An MRI also captures a detailed picture of the kidneys to allow healthcare professionals to look for structural changes or areas of concern, such as tumors. This technology uses radio waves and strong magnets. Like some CT scans, an MRI might require an injection of contrast dye.
Biopsies
In some cases, doctors may want to perform a kidney biopsy. This process involves inserting a small needle into the kidney to remove tissue. The doctor will then send the tissue to a lab for testing.
Doctors might order a biopsy when they need to identify a specific disease and see how well it may respond to treatment. They might also use a biopsy to determine the progression of kidney disease.
Positive results on multiple tests are signs that a person may have an underlying kidney issue.
The results of each of these tests help doctors get a better picture of a person’s overall kidney health. The tests can also identify markers of kidney disease and justify ordering more tests.
Once they have identified an issue with the kidneys, doctors will work to diagnose the problem and develop a treatment plan.
Many underlying conditions can lead to the loss of kidney function. A thorough diagnosis is key to finding the correct treatment in each case.
Kidney function tests are a vital part of diagnosing and treating health conditions that affect the kidneys. Some people may need regular testing, even if they do not have any symptoms.
The
- high blood pressure
- diabetes
- heart disease
- a family history of kidney disease or kidney failure
- obesity
Regular kidney function tests can help identify problems in the kidneys early, when the outlook is best.
By following a treatment plan, people can help slow the progression of kidney disease. Working directly with a doctor is the best way to monitor and manage any signs of kidney damage or underlying conditions.
