Kidney Function Testing

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Definition

What is Kidney Function Testing?

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.

Urinalysis

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.

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.

Estimated 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
  • Age
  • Gender
  • Race
  • Height
  • Weight

Why is Kidney Function Testing performed?

Kidney tests are very important for people who have diabetes, high blood pressure or heart disease. Your doctor might request these tests if:

  • They suspect your kidneys are not working properly
  • You have kidney disease and your treatment is being monitored
  • Your doctor is concerned about the levels of potassium or other minerals in your blood
  • You are taking medication that might affect your kidneys.

Precaution/Warnings

What should I know before receiving Kidney Function Testing?

Tests for kidney function don’t pose any risk. If you have any concern, don’t hesitate to consult with your doctor.

Process

How to prepare for Kidney Function Testing?

Kidney function tests don’t require any specific preparation. However, 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.

What happens during Kidney Function Testing?

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 day.

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.

Follow your doctor’s instructions about where to drop the sample off. You may need to return it either to your doctor’s office or a laboratory.

Blood samples

BUN and serum creatinine tests require blood samples taken in a lab or doctor’s office.

The technician drawing the blood first ties an elastic band around your upper arm. This makes the veins stand out. The technician then cleans the area over the vein. They 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.

What happens after Kidney Function Testing?

Kidney function testing doesn’t require any special aftercare. You may resume your daily activities unless instruced otherwise by your doctor.

If you have any questions about the Kidney Function Testing, please consult with your doctor to better understand your instructions.

Explanation of results

What do my results mean?

According to the National Kidney Foundation (NKF), a creatinine level higher than 1.2 milligrams/deciliter (mg/dL) for women and 1.4 mg/dL for men is a sign of a kidney problem.

A normal BUN level is between 7 and 20 mg/dL. A higher value could suggest several different health problems.

Any GFR result lower than 60 milliliters/minute/1.73m2 may be a warning sign of 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 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 painkillers, 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 your condition.

Depending on the laboratory and hospital, the normal range for Kidney Function Testing may vary. Please discuss with your doctor any questions you may have about your test results.

 

Hello Health Group does not provide medical advice, diagnosis or treatment.

Sources

Review Date: November 5, 2018 | Last Modified: November 5, 2018

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