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There are many different types of kidney function tests, usually involving the blood or urine. A kidney function test may check to see if the kidneys are filtering waste products too slowly. Another type of test may see if the kidneys are leaking proteins into the urine.
A doctor who thinks a person may have a problem with their kidneys may order a kidney function test, but regular testing can be helpful for all adults.
As the National Kidney Foundation note, 1 in 3 adults in the United States is at risk for kidney disease, and many people with early forms of the disease have no symptoms. It is important to diagnose and treat the condition early before it can do any permanent damage.
Kidney damage can prevent the kidneys from filtering the waste properly, leaving it to remain in the body and cause dangerous symptoms. Regular testing may help identify issues such as kidney disease in very early stages, making it possible to halt the progress of the disease.
Doctors may also order other tests to get more information about the kidney, such as imaging tests or a biopsy. Urine tests may either require a small urine sample or all of the urine a person produces in a 24-hour period.
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, such as:
- blood
- 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
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 the kidneys filter too much albumin out in the urine, it may be a sign that they are not doing their job correctly.
A urine albumin result of 30 milligrams per gram (mg/g) or less is normal. Anything higher than this may be a sign of kidney disease.
The microalbuminuria is a much more sensitive test, which can detect even tiny amounts of the protein in the urine.
People who are at higher risk for kidney disease may need to take a microalbuminuria test even if other urine protein tests come back negative.
A creatine clearance test is both a blood and urine test. It involves collecting all the urine a person creates in 24 hours, as well as taking a small blood sample.
Creatine is a waste product in the body that occurs naturally from daily use in the muscles.
Doctors compare the amount of creatine in the urine sample to the levels of creatine in the blood. This comparison shows how much waste the kidneys are filtering out, which may be an indicator of their overall health.
For blood tests, a doctor or nurse will insert a needle into a person’s arm to draw a small sample of blood. The person may need to fast beforehand or do the test first thing in the morning.
Serum creatine levels that are too high may be a sign that the kidneys are having trouble doing their job. Doctors will also order a serum creatine test as part of the creatine clearance test.
The National Kidney Foundation note that serum creatine levels above 1.2 for women or 1.4 for men may be an early sign that the kidneys are not functioning as they should. These numbers may rise further as kidney disease progresses.
Doctors may also calculate a person’s glomerular filtration rate (GFR) using this test to confirm their diagnosis or order more tests to check their results.
The GFR test takes the results of a serum creatine test and adjusts them for a number of other factors, such as age, gender, and race. The typical GFR value is 60 or above.A GFR around 60 or below is a sign of kidney problems.
The blood urea nitrogen (BUN) test checks for other waste products in the blood, such as urea nitrogen.
Urea nitrogen occurs as proteins from food break down, and elevated levels may be a sign that the kidney is not filtering these waste products effectively.
A typical BUN level falls between 7 and 20milligrams per deciliter. Higher values could be a sign of an underlying condition affecting the kidneys.
With that said, many other things can affect BUN levels, such as medications or antibiotics. A diet that is very high in protein diet may also affect levels.