Kidney Function Test (KFT) Procedure, Types and Purpose

Kidneys are your body's ultimate filtration system. They filter blood, drain waste, balance fluids, regulate blood pressure, and perform other vital functions. But here is a sobering fact: over 850 million people are estimated to live with some form of kidney disease worldwide. This amounts to more than 10% of the world’s population. 

That is why early detection of any kidney-related problem is important. To check your kidney’s health, your urologist prescribes the Kidney Function Test (KFT), also called the Renal Function Test (RFT). So, read on to learn what the different kidney function test types are, why and how they are done, and what the normal ranges are. You will also understand the step-by-step procedure and how to interpret the results.

What are Kidney Function Tests and Why They Matter?

Kidney function tests are a set of blood and urine tests. They are also sometimes paired with imaging to assess how efficiently your kidneys filter waste and maintain balance in the body. The purpose of a kidney test is to identify one or more of the following problems with your kidneys: 

• Early kidney damage 
• Known kidney disease and its progression
• The right treatments, such as medicines, diet, or more. 
• The effect of other health issues, like diabetes, hypertension, on the kidneys
• Certain medications negatively affecting the kidneys

Kidney disease often has no symptoms until later stages. Therefore, regular KFTs are especially important if you have risk factors such as diabetes, high blood pressure, a family history of kidney disease, or being over a certain age.

What Are the Types of Kidney Function Tests?

Kidney function tests are segregated into different types to identify a specific problem. The most common tests included in KFT are as follows: 

Blood Tests

• Serum Creatinine: Creatinine is a waste product from muscle breakdown. High levels in the blood suggest the kidneys aren’t clearing it properly. 
• Estimated Glomerular Filtration Rate (eGFR): This is computed using serum creatinine, age, sex (and sometimes race). eGFR estimates how much blood your kidneys filter per minute. 
• Blood Urea Nitrogen (BUN): This test measures urea (a nitrogenous waste) in blood. Elevated BUN may hint at decreased kidney function, but can also be affected by dehydration, protein intake, etc. 

Urine Tests

• Urinalysis: This is conducted for basic screening of urine for protein, blood, sugar, casts, crystals, etc. A urinalysis can detect damage to your kidneys or other issues. 
• Urine albumin/albumin-to-creatinine ratio (uACR): This test checks for small amounts of protein (albumin) in your urine. Even small amounts (microalbuminuria) can signal early kidney damage. 
• 24-hour urine collection (for creatinine clearance or total protein): This test gives a clearer picture of how much creatinine or protein you excrete in the urine. That is why a 24-hour urine collection is important to estimate true GFR more accurately. 

Other/Optional Tests

• Electrolytes (sodium, potassium, phosphorus, etc.)
• Acid-base balance (e.g., bicarbonate)
• Imaging (ultrasound, CT scan) to assess kidney structure if needed
• Sometimes kidney biopsy is performed in cases where more detailed tissue-level information is needed. 

Normal Ranges in Kidney Function Tests

Kidney function test normal range can differ slightly between labs, populations, age, and sex. But here are commonly accepted values:

Stages of CKD are often defined using eGFR thresholds:

• Stage 1: eGFR ≥ 90 (with evidence of kidney damage)
• Stage 2: 60-89
• Stage 3a: 45-59
• Stage 3b: 30-44
• Stage 4: 15-29
• Stage 5: < 15 (kidney failure)

What is the KFT Procedure Step by Step?

Before going for the test, you might have multiple questions about the preparation or how KFT is done. So, here’s the KFT procedure step by step for you: 

1. Doctor’s Order / Indication

Firstly, the clinician will decide whether you need to get a KFT done. They will assess certain risk factors, symptoms, and perform a routine checkup to make a decision. 

2. Preparation
   • For blood tests, you will be asked to fast (nothing by mouth) for a few hours, especially if other tests are being done.
   • Tell your doctor about medications, supplements, and herbal remedies. They can interfere with results.
   • For a urine test, sometimes you’ll need a clean-catch sample, or for a 24-hour collection, instructions will be given.
3. Sample Collection
   • A nurse/phlebotomist will draw blood from a vein (usually your arm). They will collect a few tubes if your doctor has ordered multiple tests together. 
   • For urine collection, you will either have a spot sample (morning may be preferred) or a 24-hour collection. For 24 hours, you collect all urine over a full day in a large container. You will have to follow the instructions carefully. The most common instructions will be like start after the first morning pee, collect each time, and end on the morning next day.
4. Transport / Laboratory Analysis

The blood and urine will then be sent to a clinical laboratory. The sample will be tested for creatinine, BUN, albumin, electrolytes, etc. The lab also computes eGFR based on the standard formula.

5. Results & Interpretation

Once lab results are in (often same day to a few days, depending), the doctor looks at values with respect to normal ranges, patient history, and risk factors. The key things they check for are: Is eGFR above or below thresholds? Is there albuminuria or proteinuria? Are there electrolyte imbalances?

6. Follow-up

Depending on results:

• If everything is normal, routine monitoring will be advised (especially if risk factors are present).
• If mild abnormalities are present, your doctor will suggest certain interventions. For example, lifestyle changes (diet, fluid intake), controlling blood pressure/sugar, and avoiding nephrotoxic drugs.
• If there is a moderate-to-severe abnormality, your physician will refer you to a nephrologist, possibly for imaging, more frequent monitoring, or treatment.

Also Read: Foods that cause Kidney Stones

Who Should Get a KFT Done?

You should ask your physician for a KFT if you are one or more of the following: 

• Individuals with diabetes
• People with high blood pressure (hypertension)
• Family history of kidney disease
• Those with swelling in legs, feet, or around the eyes 
• People experiencing fatigue, nausea, or loss of appetite 
• Patients on long-term medications (like painkillers, antibiotics, chemotherapy drugs) 
• Adults above 60 years 
• Those with cardiovascular diseases 
• Individuals with abnormal urine output
• People recovering from severe infections

Keep Your Kidneys’ Health in Check With the Right Guidance! 

Kidney function tests are simple yet powerful tools. They give your physician insight into how well your internal filtration system is working, long before serious symptoms appear. As CKD affects nearly one in ten people globally, many people remain unaware. Therefore, you should go for regular and correct testing. 

So, reach out to Apollo Spectra today. We have a team of experienced physicians and urologists. They will guide you through the right medications and treatment approaches based on the results of different kidney function test types. You will get the best care from the most trusted hospital in the country.