What Are the Different Types of Kidney Tests?

Every minute of the day, your kid­neys are hard at work.

The kid­neys — two bean-shaped organs that sit just below your rib cage — fil­ter waste and excess water out of your blood to cre­ate urine. When they’re func­tion­ing cor­rect­ly, they fil­ter about half a cup of blood per minute. How­ev­er, when your kid­neys don’t work prop­er­ly, waste col­lects in your body, mak­ing you sick. If kid­ney dis­ease gets worse, it can progress into kid­ney fail­ure — a dis­ease that’s fatal if not treated. 

While kid­ney dis­ease can’t be reversed, it can often be treat­ed if it is found in its ear­li­est stages. Unfor­tu­nate­ly, since kid­ney dis­ease usu­al­ly doesn’t cause symp­toms ear­ly on, many peo­ple only learn they have it once it has pro­gressed to an advanced state. In fact, 9 out of 10 peo­ple who are liv­ing with kid­ney dis­ease aren’t aware of it. 

The only way to know if your kid­neys are healthy is to get test­ed. Your provider may rec­om­mend a kid­ney test if you have: 

  • A con­di­tion that puts you at high risk for kid­ney dis­ease, like high blood pres­sure, dia­betes, or heart disease 
  • A fam­i­ly his­to­ry of kid­ney failure 
  • Symp­toms of kid­ney prob­lems, like blood in your urine, fre­quent­ly hav­ing to uri­nate, or pain with urination

Also read: Which Health Con­di­tions Could Put Me at High­er Risk for Heart Disease?

Urine Tests: Do You Have Signs of Kid­ney Disease? 

Your urine reveals a lot about what’s hap­pen­ing inside your body, from dehy­dra­tion to infec­tions to preg­nan­cy. It also offers a look into the state of your kid­neys. Dam­aged kid­neys may leak a pro­tein called albu­min into your urine. Hav­ing albu­min in urine (albu­min­uria) may be one of the first signs that you’re suf­fer­ing from kid­ney disease. 

Providers can check for albu­min­uria in one of two ways: 

Dip­stick Test 

The dip­stick urine test is sim­ple: You give a urine sam­ple at your provider’s office or lab, and the provider places a dip­stick (a chem­i­cal­ly treat­ed strip of paper) into the sam­ple. If the lev­el of albu­min in your urine is above what’s con­sid­ered nor­mal, the dip­stick changes color. 

This is just the first step. While it tells your provider if you have high albu­min lev­els, it doesn’t give an exact measurement.

Urine Albu­min-to-Cre­a­ti­nine Ratio 

The urine albu­min-cre­a­ti­nine ratio test goes more in-depth. It mea­sures the amount of albu­min in your urine, as well as the amount of cre­a­ti­nine (a nor­mal waste prod­uct found in your urine), and com­pares the two num­bers to cal­cu­late your urine albu­min-cre­a­ti­nine ratio (uACR). A nor­mal test result is a uACR of 30 or low­er. Any­thing above that could indi­cate that you have kid­ney dis­ease or are at an increased risk for kid­ney fail­ure, heart attack, or stroke. 

24-Hour Urine Collection 

A uACR test might be more com­plex than a quick trip to the lab. Your provider may need you to col­lect all of your urine for a full 24 hours so they can see how much albu­min goes into your urine dur­ing that time. The 24-hour test is often used as a fol­low-up after an abnor­mal result from a test based on a sin­gle sam­ple. It’s the most accu­rate way to mea­sure the amount of albu­min in your urine — but it’s not usu­al­ly ordered right away since it’s not as con­ve­nient as a one-time test. 

CALL TO ACTION/FEATURED TEXT: To learn more about kid­ney test­ing, sched­ule an appoint­ment with a Duly Health and Care nephrol­o­gist or your pri­ma­ry care provider

Blood Tests: How Are Your Kid­neys Functioning? 

Blood tests are anoth­er way to check kid­ney func­tion. There are sev­er­al types of blood tests, and you may need to have more than one. Three of the most com­mon are serum cre­a­ti­nine, glomeru­lar fil­tra­tion rate, and blood urea nitro­gen (BUN). 

Serum Cre­a­ti­nine Test 

Your kid­neys are respon­si­ble for fil­ter­ing cre­a­ti­nine — a waste prod­uct that your body makes nat­u­ral­ly — out of your blood. A serum cre­a­ti­nine test mea­sures how much cre­a­ti­nine is in your blood. If there is too much, it could be a sign that your kid­neys aren’t fil­ter­ing it out as well as they should — and that can indi­cate pos­si­ble kid­ney dis­ease. Because cre­a­ti­nine lev­els can vary based on your age, weight, diet, activ­i­ty lev­el, and oth­er fac­tors, there is no stan­dard lev­el to mea­sure your results against, but a low­er num­ber is con­sid­ered better. 

Glomeru­lar Fil­tra­tion Rate Test 

Because a serum cre­a­ti­nine test alone might not give enough infor­ma­tion to clear­ly mea­sure your kid­ney func­tion, it is usu­al­ly used along with addi­tion­al tests, such as your esti­mat­ed glomeru­lar fil­tra­tion rate (eGFR). The eGFR mea­sures the amount of blood that your kid­neys fil­ter out each minute. Since it’s a com­pli­cat­ed test, providers typ­i­cal­ly don’t mea­sure your eGFR direct­ly — they esti­mate it based on your serum cre­a­ti­nine, age, sex, height, and weight. A high­er rate is bet­ter. While the def­i­n­i­tion of a nor­mal” test result varies based on age, a val­ue of less than 60 is usu­al­ly a sign that there’s a prob­lem with your kid­neys, and a val­ue of less than 15 indi­cates kid­ney failure. 

Blood Urea Nitro­gen Test 

Urea nitro­gen is anoth­er waste prod­uct that your body makes nat­u­ral­ly. A blood urea nitro­gen (BUN) test checks how much urea nitro­gen is in your blood. It’s nor­mal to have a lit­tle bit of urea nitro­gen in your blood. How­ev­er, greater amounts could mean you have a con­di­tion dis­rupt­ing kid­ney func­tion. The amount that’s con­sid­ered nor­mal changes based on your age and sex, and typ­i­cal­ly increas­es as you get old­er. A BUN test is typ­i­cal­ly includ­ed in a Basic and Com­pre­hen­sive Meta­bol­ic Pan­el ordered by your pri­ma­ry care physi­cian dur­ing your annu­al phys­i­cal. A BUN test doesn’t define kid­ney fail­ure by itself. But if your result is high­er than it usu­al­ly is, and your cre­a­ti­nine lev­els are also high, you’re like­ly expe­ri­enc­ing kid­ney failure. 

Also read: Blood Work Basics: What to Know About Your Test 

When Your Provider Needs More Infor­ma­tion
Urine and blood tests are key for diag­nos­ing kid­ney prob­lems, but they don’t always tell the entire sto­ry. Your provider may want you to take oth­er types of tests to fur­ther exam­ine your kid­neys or mon­i­tor exist­ing prob­lems. Some of the oth­er tests you may need include: 

  • Blood pres­sure mon­i­tor­ing. High blood pres­sure can make kid­ney prob­lems worse, and dam­aged kid­neys have trou­ble reg­u­lat­ing blood pressure. 
  • Imag­ing tests, like com­put­er­ized tomog­ra­phy (CT) scans, mag­net­ic res­o­nance imag­ing (MRI), or ultra­sounds. These tests cre­ate detailed images of your kid­neys so your provider can look for signs of dam­age or dis­ease and see how well blood flows to your kidneys. 
  • Biop­sy. A biop­sy is a pro­ce­dure where your provider removes a small sam­ple of kid­ney tis­sue to exam­ine under a micro­scope for evi­dence of dam­age or disease.

The Next Steps After Kid­ney Testing 

If you find out that you have kid­ney dis­ease, it’s crit­i­cal to start treat­ment as soon as pos­si­ble and keep up with all of your check-ups. The ear­li­er you begin treat­ment, the greater your like­li­hood of keep­ing it from get­ting worse. And if you can pre­vent it from get­ting worse and you con­tin­ue treat­ment, you may still be able to live a long life — and keep up your qual­i­ty of life.

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