Kidney Function Tests

Understanding Your Renal Function Test Results

urine sample, urine specimen
A Urine Sample For Urinalysis.

What the Kidneys Do

In order to understand kidney function tests, also known as a renal panel, it is important to understand what the kidneys do. The kidneys filter the blood and remove unwanted waste from the bloodstream.  They also remove excess water from the body, helping to regulate blood pressure and the fluid balance of the body.

When the kidneys are functioning well, there is very little unwanted waste in the body.

When these waste levels in the blood begin to climb, they can indicate that the kidneys are no longer functioning as well as they should.

Why Kidney Function Tests Are Performed

Kidney function tests are performed for a variety of reasons, including something as simple as a yearly checkup, or a urinary tract infection is suspected. They may also be performed if an individual is ill and a diagnosis has not been made, as a screening test for a patient planning or recovering from surgery, or as a way to track kidney disease. Urinary tract infections are common after surgery, and some patients experience kidney dysfunction after a procedure, so these tests are frequently performed on patients recovering from surgery.

Kidney function tests are a reliable way of testing the kidneys, but it is important to remember that they can also change dramatically with illness or dehydration. Many individuals can have an acute (temporary) problem with the kidneys that resolves after receiving fluids or other treatment.

Common Kidney Function Tests

Urinalysis

The urinalysis is the most common and basic test that is performed on urine, and is not strictly considered a kidney function test but is an examination of urine. It is used to detect urinary tract infections, the presence of blood and protein in the urine. This test can often rule out the need for further testing, or can be a sign that more tests should be performed.

Blood is not normal in urine, but can be the result of a woman’s menstrual cycle. Protein is also not typical in urine. Both of these may be present during a urinary tract infection.

For this test, a small sample of urine is collected, typically using the “clean catch” method, where the individual starts to urinate then collects a sample of urine from the middle of the urine stream.

Serum Creatinine

Normal Lab Values: Men: .7-1.3, Women: .6-1.1 mg/dl

This test is a blood test that looks at how much creatinine is in the blood stream. One of the primary functions of the kidneys is to remove creatinine, which is the waste product of muscle breakdown, from the bloodstream. Too much creatinine in the blood can mean that the kidneys are not performing their job. Very high levels of creatinine can mean that the patient is experiencing kidney failure, which can be a temporary condition or a permanent problem.

Estimated Glomerular Filtration Rate

Normal Lab Value 90-120 ml/minute, 60 ml/minute or less indicates kidney damage may be present

Kidneys can filter up to 150 quarts of blood each day in the body of the average adult. The Estimated Glomerular Filtration Rate (EGFR) is a way of estimating the ability of the kidneys to filter blood. Using a formula that includes creatinine level, a lab can estimate the number of liters of blood the kidneys are filtering.

BUN

Normal Lab Value 8-25 mg/100ml

The BUN, or Blood Urea Nitrogen test, is another way to determine if the kidneys are successfully filtering the blood. Urea nitrogen is normal in the blood at small levels, but higher levels may indicate that the individual is experiencing kidney problems.

24 Hour Urine or Timed Urine Sample

This test requires that urine be collected for an entire 24 hour period, there are other variations of this test that require urine to be collected for 4 hours, 12 hours, or another length of time. Kidney function can fluctuate through the course of a day, so this test provides a look at the average function of the kidneys.

The lab typically provides the patient with a jug that is kept in the refrigerator while the sample is being collected. The test begins by discarding the first urine in the 24 hour period, and collecting each sample that follows. At the end of the 24 hour period, the patient should attempt to empty their bladder one final time and collect the sample.

For many patients, remembering to collect the urine each time is a challenge, and may result in restarting the test after a sample is flushed. Some individuals will leave a reminder taped to the toilet lid so they do not forget to collect the urine each time.

Source

Renal Panel. Lab Tests Online. Access October, 2015. https://labtestsonline.org/understanding/analytes/renal-panel/tab/test

Continue Reading