RENAL FUNCTION TEST (RFT)
ALSO CALLED AS KIDNEY FUNCTION TEST (KFT)
Analysis of blood and urine samples can be essential for the evaluation of kidney (renal) function. The following are some of the basic renal function tests.
Blood urea nitrogen (BUN) provides a rough measurement of the glomerular filtration rate, the rate at which blood is filtered in the kidneys. Urea is formed in the liver as an end product of protein metabolism and is carried to the kidneys for excretion. Nearly all kidney diseases cause inadequate excretion of urea, elevating BUN levels in the blood. (Other causes of high BUN levels include gastrointestinal bleeding and steroid treatment.) It can be done to determine the amount of urea nitrogen in the blood.
Creatinine is a breakdown product of creatine, an important component of muscle. The production of creatinine depends on muscle mass, which varies very little. Creatinine is excreted exclusively by the kidneys, and its level in the blood is proportional to the glomerular filtration rate. The serum creatinine level (serum is the clear liquid that remains after whole blood has clotted) provides a more sensitive test of kidney function than BUN because kidney impairment is almost the only cause of elevated creatinine. It can also be measured with a urine test.
Creatinine clearance rate determines how efficiently the kidneys are clearing creatinine from the blood and serves as an estimate of kidney function. For renal function test, urine and serum levels of creatinine are measured, as well as the volume of urine excreted over a 24-hour period. The creatinine clearance rate is then calculated and expressed as the volume of blood, in milliliters, that can be cleared of creatinine in 1 minute. A low creatinine clearance value indicates abnormal kidney function. It requires both a urine and blood sample.
OVERVIEW 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.
SYMPTOMS OF KIDNEY PROBLEMS
Symptoms that may indicate a problem with your kidneys include:
- 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.
TYPES 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 disease.