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Kidney Function Tests Explained

Timely and regular testing is the best way to determine kidney function levels and diagnose chronic kidney disease (CKD). Taking action at each stage of kidney disease can help keep your kidneys healthy and working longer. Kidney function tests—or renal function tests—are simple and can be done in the comfort of your doctor’s office.

If you receive a kidney disease diagnosis, you’ll be tested regularly to track your progression. With early diagnosis and a personalized treatment plan, you may be able to slow the progression of kidney disease and preserve your remaining kidney health.

Who should get a kidney function test?

Be your own advocate by talking to your doctor about any concerns you have about your kidney health. CKD should be treated as early as possible to slow progression. While regular kidney function tests are beneficial for everyone, it’s especially important to get tested once a year if you are:

At higher risk for kidney disease

Those with conditions such as diabetes, high blood pressure, obesity, or lupus should consider themselves at higher risk for kidney disease. Also, your age, weight, family history, and overall health may put you at greater risk for CKD. If you have any of these risk factors, talk to your doctor about getting tested at least once a year.

Experiencing symptoms of CKD

If you have any potential CKD symptoms, talk to your doctor immediately about scheduling laboratory tests to identify whether or not you’re in a normal range of kidney function.

Diagnosed with CKD

For those already diagnosed with chronic kidney disease, a regular kidney function test can help your nephrologist (kidney doctor) develop or adjust your personalized treatment plan to help preserve your overall kidney health.

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What tests are done to check kidney function?

There are several different types of tests your doctor might order—each serving a different purpose—depending on your unique health condition.

Blood tests

  1. A serum creatinine test measures the level of creatinine in your blood—a waste product that is produced when your muscles are used. Results greater than 1.2 for women and 1.4 for men may indicate possible kidney damage.
  2. A blood urea nitrogen (BUN) test measures the level of urea nitrogen in your blood—a waste product that is produced when your body breaks down proteins in food. BUN levels of 20 or greater may indicate decreasing kidney function, or dehydration.
  3. A renal function panel measures the amount of certain substances in your blood. High or low amounts of a given substance can signal improper kidney function.

Urine tests

  1. An albuminuria-to-creatinine ratio (ACR) test measures the amount of protein—or albumin—in urine. Results higher than 30 mg/gm could mean a possible sign of kidney disease.
  2. A urine protein test measures the level of protein released into urine by the kidneys. Normal elimination is less than 150 mg/day and less than 30 mg of albumin/day. Excess amounts of protein in the urine can lead to a condition called proteinuria.
  3. A urinalysis detects acidity (pH), bacteria, blood, white blood cell levels, pus, or excess amounts of protein in urine, which can all be signs of kidney damage.

Imaging tests

  1. A CT scan provides a series of detailed X-ray images of the kidneys in order to assess any damage or abnormalities.
  2. Ultrasound imaging sends sound waves into your body to create images that measure the size, location, and shape of the kidneys and related structures, such as the ureters and bladder. These images can help detect cysts, tumors, abscesses, obstructions, fluid collection, and infection within or around the kidneys.

Other tests

  1. A kidney biopsy reveals what an ultrasound or other tests cannot detect. By extracting a kidney tissue sample, your doctor can determine the primary causes of abnormal kidney function tests—such as scarring, swelling, and protein deposits.

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How is chronic kidney disease (ckd) diagnosed?

Abnormal kidney function test results may signal the first step of your CKD journey. After a simple blood test, your doctor will help determine your unique needs by:
1. Calculating your glomerular filtration rate (GFR)

Your GFR is a measurement of how well your kidneys are functioning. While your exact GFR cannot be measured directly, your estimated glomerular filtration rate (eGFR) is a calculation that indicates your level of kidney function, based on multiple factors. One of these factors is how much creatinine is in your blood. After measuring your creatinine levels in a serum creatinine test, your eGFR can be calculated using age, gender, and body size.

2. Determining your kidney function level

Normal kidney function levels can vary by age. However, if your eGFR is 30–44, your primary care physician will likely refer you to a nephrologist for additional tests. These tests will help you detect abnormalities that signal CKD.

3. Developing a treatment plan

With your eGFR blood test and additional test results, your doctor will be able to measure your level of kidney function. From there, you’ll receive a full diagnosis and personalized treatment plan. The sooner your doctor can confirm a diagnosis for CKD, the earlier you can get the care and support you need.

The importance of kidney function tests

Getting tested to check your kidney health is easy, non-invasive, and critical to your current and future well-being. Whether you and your doctor are seeking a diagnosis or monitoring how well your treatment plan is working, acting early is always best. For CKD, the sooner your doctor can confirm a diagnosis, the earlier you can get started on an effective treatment plan to help preserve kidney function and slow progression.

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Use this list of questions to start a discussion with your kidney doctor and other care team members.
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