of Kidney Function Tests
You have two kidneys on either side of your spine that are each
approximately the size of a human fist. They’re located posterior to your
abdomen and below your rib cage.
Your kidneys play several vital roles in maintaining your health.
One of their most important jobs is to filter waste materials from the blood
and expel them from the body as urine. The kidneys also help control the levels
of water and various essential minerals in the body. In addition, they’re
critical to the production of:
- vitamin D
- red blood cells
- hormones that regulate blood pressure
If your doctor thinks your kidneys may not be working
properly, you may need kidney function tests. These are simple blood and urine
tests that can identify problems with your kidneys.
You may also need kidney function testing done if you have
other conditions that can harm the kidneys, such as diabetes or high blood
pressure. They can help doctors monitor these conditions.
of Kidney Problems
Symptoms that may indicate a problem with your kidneys
- high blood pressure
- blood in the urine
- frequent urges to urinate
- difficulty beginning urination
- painful urination
- swelling of the hands and feet due to a buildup
of fluids in the body
A single symptom may not mean something serious. However,
when occurring simultaneously, these symptoms suggest that your kidneys aren’t
working properly. Kidney function tests can help determine the reason.
of Kidney Function Tests
To test your kidney function, your doctor will order a set
of tests that can estimate your glomerular filtration rate (GFR). Your GFR
tells your doctor how quickly your kidneys are clearing waste from your body.
A urinalysis screens for the presence of protein and blood
in the urine. There are many possible reasons for protein in your urine, not
all of which are related to disease. Infection increases urine protein, but so
does a heavy physical workout. Your doctor may want to repeat this test after a
few weeks to see if the results are similar.
Your doctor may also ask you to provide a 24-hour urine
collection sample. This can help doctors see how fast a waste product called
creatinine is clearing from your body. Creatinine is a breakdown product of muscle tissue.
Serum Creatinine Test
This blood test examines whether creatinine is building up
in your blood. The kidneys usually completely filter creatinine from the blood.
A high level of creatinine suggests a kidney problem.
According to the National Kidney
Foundation (NKF), a creatinine level higher than 1.2 for women and 1.4 for
men is a sign of a kidney problem.
Blood Urea Nitrogen (BUN)
The blood urea nitrogen (BUN) test also checks for waste
products in your blood. BUN tests measure the amount of nitrogen in the
blood. Urea nitrogen is
a breakdown product of protein. However, not all elevated BUN tests are due to
kidney damage. Common medications, including large doses of aspirin and some
types of antibiotics, can also increase your BUN. It’s important to tell your
doctor about any medications or supplements that you take regularly. You may
need to stop certain drugs for a few days before the test.
A normal BUN level is between 7 and 20. A higher value could
suggest several different health problems.
Estimated Glomerular Filtration Rate (GFR)
This test estimates how well your kidneys are filtering
waste. The test determines the rate by looking at factors, such as:
- test results, specifically creatinine levels
Any result lower than 60 may be a warning sign of kidney
the Tests Are Obtained
Kidney function tests usually require a 24-hour urine sample
and a blood test.
24-Hour Urine Sample
A 24-hour urine sample is a creatinine clearance test. It
gives your doctor an idea of how much creatinine your body expels over a single
On the day that you start the test, urinate into the toilet
as you normally would when you wake up.
For the rest of the day and night, urinate into a special
container provided by your doctor. Keep the container capped and refrigerated
during the collection process. Make sure to label the container clearly and to
tell other family members why it’s in the refrigerator.
On the morning of the second day, urinate into the container
when you get up. This completes the 24-hour collection process.
Cap and label the container, and follow your doctor’s
instructions about where to drop it off. You may need to return it either to
your doctor’s office or a laboratory.
BUN and serum creatinine tests require blood samples taken
in a lab or doctor’s office.
The technician drawing the blood will tie an elastic band
around your upper arm. This makes the veins stand out. The technician will
clean the area over the vein. They will then slip a hollow needle through your
skin and into the vein. The blood will flow back into a test tube that will be
sent for analysis.
You may feel a sharp pinch or prick when the needle enters
your arm. The technician will place gauze and a bandage over the puncture site
after the test. The area around the puncture may develop a bruise over the next
few days. However, you shouldn’t feel severe or long-term pain.
of Early Kidney Disease
Your doctor will focus on treating the underlying condition
if the tests show early kidney disease. Your doctor will prescribe medications
to control the blood pressure if the tests indicate hypertension. They’ll also
suggest lifestyle and dietary modifications.
If you have diabetes, your doctor may want you to see
an endocrinologist. This
type of doctor specializes in metabolic diseases and can help ensure that you
have the best blood glucose control possible.
If there are other causes of your abnormal kidney function
tests, such as kidney stones and excessive use of pain killers, your doctor
will take appropriate measures to manage those disorders.
Abnormal test results mean you’ll probably need regular kidney
function tests in the months ahead. These will help your doctor keep an eye on