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Kidney Function Test (KFT): Purpose, Types and Procedure



Kidneys play a critical role in eliminating metabolic body wastes and in maintaining the body's overall water and electrolyte balance. The kidney function tests (KFT) help you understand whether your kidneys are working efficiently or not by examining how effectively your kidneys are removing wastes from your body. A 24-hour urine sample, a blood test, or both may be required for kidney function evaluation.

What Do Your Kidneys Do?

Your genito-urinary system includes your kidneys, which are positioned just below your left rib cage at the back of your belly. Kidneys help your body in removing waste products through urine excretion. The additional functions of the kidneys include:

  • Production of blood pressure-maintaining hormones
  • Production of the oxygen-carrying red blood cells that circulate through your body
  • Production of vitamin D, which keeps your muscles and bones healthy

So, it is evident that taking care of your kidneys is of utmost importance. You can get a kidney function test (KFT) for a proper evaluation of your kidneys' current health.

What Symptoms Can be Caused By Kidney Problems?

Symptoms that may indicate a problem with your kidneys include:

  • Frequent urges to urinate
  • Difficulty beginning urination
  • Pain during urination
  • High blood pressure
  • Blood in the urine
  • Swelling of the hands and feet

Your doctor will evaluate your symptoms, correlates it with the test findings, and arrive at a diagnosis. Also, a single symptom may not always mean something serious.

What Are Kidney Function Tests?

Bodily waste or toxic substances including excess fluid are usually removed from the bloodstream by healthy functioning kidneys. Blood specimens and urine tests indicate how properly your kidneys are working and how effectively wastes are excreted from the body. Urine tests can help detect whether the kidneys are leaking any amount of excessive protein, which is a sign of kidney damage. 

Here we will discuss various tests that are used to understand kidney function. Most of these kidney function tests assess the glomerular filtration rate (GFR). GFR measures how well your kidneys remove waste from your system.

What are The Different Types of Kidney Function Tests (KFT)?

To diagnose the proper health of your kidneys your physician may prescribe different types of kidney function tests. The following are the different tests that are commonly included in KFT:

Serum Creatinine

The body's metabolism produces creatinine as a waste product. The kidneys remove it from the blood and excrete it via urination. Generally, creatinine is almost eliminated from the body through the kidneys. In this way, our bodies maintain a low level of creatinine because this creatinine excretion is an ongoing process. Therefore, a high creatinine level could be a sign of kidney issues. In general,

  • For adult men, the normal range of serum creatinine lies between 0.74 to 1.35 mg/dL
  • For adult women, the normal range of serum creatinine lies between 0.59 to 1.04 mg/dL

Uric Acid

When our body chemically breaks down organic compounds metabolically, uric acid is created. The kidneys filter and eliminate this uric acid waste product through urine. Therefore, both higher or lower uric acid levels could indicate kidney damage.

In general, the normal range of uric acid lies between 3.7-9.2 mg/dL.

Blood Urea Nitrogen (BUN)

When the body breaks down proteins, it results in urea nitrogen production. Urea nitrogen is also a waste product that the kidneys eliminate through urine. Generally, the level of urea nitrogen in your blood should fall between specific limits. Other than kidney issues, some medications may also cause a rise in urea nitrogen levels in our blood. Therefore, if your BUN level is greater than usual, talk to your doctor for a detailed diagnosis and also inform him about your current medications.

In general, the normal range of BUN lies between 7-25 mg/dL.


Electrolytes are minerals present in the blood and body fluids that facilitate several body functions. They can be positively or negatively charged. An electrolyte test helps monitor the body’s electrolyte levels and is a strong indicator of how well your kidneys are functioning. Sodium, potassium, and chloride are some of the main electrolytes. The normal range for each electrolyte can vary to some extent in men and women, and different age groups. 

Estimated Glomerular Filtration Rate (eGFR) 

The GFR calculates your kidneys' ability to filter waste materials from the body. Your normal GFR results may not always correspond to your normal serum creatinine level. To evaluate your proper renal function, it is, therefore, preferable to estimate glomerular filtration rate or eGFR, also known as the "gold standard" measurement. Your serum creatinine, age, race, and sex, all will be used to estimate your GFR. Because this test result roughly equates to your remaining kidney function, this test helps you get easy-to-interpret information regarding the degree of your kidney damage. 

In general,

  • The normal level of GFR is considered at 60 or above
  • A below 60 GFR test result may indicate kidney-related diseases
  • A below 15 GFR test results may indicate severe kidney failure

Additionally, your doctor may also conduct 24-hour urine testing, such as:

  • Microalbuminuria: This test searches for a specific protein known as albumin in your urine. In general, a urine albumin level below 30 is considered normal, whereas an albumin level above 30 indicates that you may have kidney problems.
  • Urinalysis: This test examines your urine and looks for blood and proteins.

Purpose of Kidney Function Tests

Conditions such as high sugar levels or diabetes and high blood pressure or hypertension are two major conditions that have an impact on how well the kidneys work. If someone has either of these conditions, their doctor may prescribe KFT or kidney function tests to monitor their progress.

Similarly, if one is presented with symptoms that point to kidney problems, the person may also require a kidney function test. Among these symptoms are:

  • increasing blood pressure
  • blood present in the urine
  • frequent urination
  • difficulty urinating
  • pain during urination
  • buildup of fluids in the body leading to swelling of the hands and feet

Are There any Preparations Needed Before the Kidney Function Test (KFT)?

No, you do not need to take any preparation before your KFT test. You can either visit your nearest laboratory for KFT tests or can have your blood drawn for the KFT test at your home by trained professionals.

Procedure of Kidney Function Tests

As mentioned in the article earlier, 24-hour urine samples and blood tests are usually key requirements for kidney function tests.

Urine Test After 24 Hours

A 24-hour urine sample culture is often used to determine creatinine clearance tests. It helps to identify the level or amount of creatinine a patient's body removes in a single day. Doctors provide a special container to store urination. During the collection process, it is advised to keep the container sealed and refrigerated. Make sure to properly mark the container and explain the reason to store it in the refrigerator to other family members.

Blood Samples

BUN and serum creatinine tests both require blood specimens to be taken in a lab or health clinic.  Before drawing blood, the technician ties a band around the upper arm. This highlights the veins from which blood needs to be drawn. After that, the technician cleans the area and inserts a hollow needle into the patient's vein through the skin. The blood will be collected with the help of a test tube and sent to a lab for further analysis.

When Should You Go for a Kidney Function Test?

KFT helps you detect any kidney-related health conditions that you might have. However if you have any of the following health conditions, or have certain lifestyle habits, kidney function tests are more crucial for you:

  • Any kidney-related health conditions
  • Any symptoms related to kidney damage
  • Any kidney-damaging health conditions, like high blood pressure or diabetes
  • Have a family history of kidney-damaging conditions
  • Aged above 60
  • A heavy smoker

If you think you have any of the above conditions, check your kidney health today. Book a kidney function test online and get tested from the comfort of your home by trained professionals.

Who Can Perform a Kidney Function Test (KFT)?

Generally, a healthcare provider, known as a phlebotomist, or any trained professional will draw your blood, for your kidney function tests. Your blood samples will be then sent to diagnostic laboratories for further diagnosis.

Can Your Kidney Function Get Better?

Kidney disease can be treated if diagnosed well within time. Advanced treatment options are also available to help delay or prevent kidney failure in severe kidney damage.

No matter what your results are:

  • Maintain your blood pressure, blood glucose, and blood cholesterol in your target range.
  • Cut back on salt and choose a balanced diet for kidneys.
  • Keep yourself physically active.
  • Take medicines the way your provider tells you to.
  • Get tested from time to time to keep an eye on kidney health.

Are Kidney Function Tests Risky?

The KFT blood tests are quite common and have no significant risk factors. However, at the time of blood collection, you may feel a little discomfort or pain which will go away eventually.


Kidney function tests help you ensure that your kidneys are functioning properly. Your body's ability to eliminate waste materials is dependent on your kidneys’ health. You may face poor kidney functions due to health conditions like diabetes, high blood pressure, or due to other health-related concerns. 

Book your kidney function test at Metropolis Healthcare which provides a wide range of blood testing and health check-up services. Qualified blood collection technicians will collect your blood by visiting your home at your convenience. Your blood sample will be processed at their cutting-edge laboratory using the 8-state MET Protocol. Your test reports will be sent to you through email. To download or share your reports, you may also download the Metropolis TruHealth app.

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