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What is the kidney function test (KFT) and why is it done?

The kidneys are a pair of bean-shaped organs present on either side of the spinal cord. The kidneys are of the size of our fists. They play a critical

The kidneys are a pair of bean-shaped organs present on either side of the spinal cord. The kidneys are of the size of our fists. They play a critical role in our body and their main functions are as follows:

  • It filters all the waste and harmful materials from the bloodstream and expels them from the body in the form of urine. 
  • It helps to maintain the water level and other essential minerals in the body. 
  • It helps in the production of various important things such as Vitamin D, red blood cells, and several hormones that help in the regulation of blood pressure. 

When is a KFT test required?  

  • The kidney function test or the KFT test is recommended by the doctor when one or more of these symptoms are seen in the patient:
  • The patient is consistently having high blood pressure. 
  • There is blood in the urine. 
  • The patient is feeling the urge to urinate very frequently. 
  • The patient cannot urinate easily. 
  • The process of urination is painful 
  • Swelling up of limbs due to the accumulation of body fluids. 
  • When these symptoms are seen in the patient, the medical practitioner recommends the patient to take a KFT test. A KFT test can be suggested by the doctor for the following purposes too:
  • Detection of renal (about the kidney) diseases. 
  • Monitor the efficacy of treatment on diseases of the kidney. 
  • Detects if the patient is at risk of any renal disease. 
  • To check if conditions like high blood pressure and diabetes have affected the kidneys. 
  • To evaluate or detect any chronic disease of the kidneys. 

What are the components of Kidney Function Tests?

Four different tests are done to get an understanding of how well the kidneys are working. The four components that are tested are Blood Urea Nitrogen, Uric Acid, and Creatinine.

  • Blood Urea Nitrogen

The Blood Urea Nitrogen is indicative of the amount of urea present in the bloodstream. Urea is a by-product of the proteins assimilated by our digestive system. The urea in turn contains nitrogen. Thus, the urea present in our bloodstream is indicative of the amount of nitrogen that is present in our blood; albeit in the form of urea. This excess urea is expelled from our body by the kidneys in the form of urine. Medications like aspirin may increase the blood urea nitrogen level, so some medication may be required to stop before undertaking this test. 

An increased level of urea nitrogen may be indicative of kidney failure, shocks, burn injuries, dehydration, blockage of the urinary tract due to stones in the kidney, and prostate gland enlargement. 

Low levels of blood urea nitrogen may be due to liver failure and nephrotic syndrome. 

  • Uric Acid:

Uric Acid is formed by the breakdown of purines- which are an essential part of our DNA. It is also produced from the breakdown of foods containing high protein during digestion. Uric acid is expelled from our body through urine and stool after it is filtered by the kidney. The testing of uric acid in the blood is indirectly indicative of the proper functioning of the kidney. 

High levels of uric acid in the bloodstream are known as hyperuricemia and may be indicative of the following conditions; kidney disease, some types of cancer, gout, alcohol addiction, tophi, and hypothyroidism. 

Low levels of uric acid in the bloodstream may be caused by low levels of protein consumption and severe kidney diseases. 

  • Creatinine: 

Creatinine is formed by the process of the breakdown of muscles in the body. The entirety of creatinine produced in our body is excreted via urine after it is filtered out of the bloodstream by the kidney. 

High levels of creatinine found in the bloodstream are indicative of nephrotoxic drugs, kidney failure, hypothyroidism, and urinary tract obstruction. High levels may be caused by excess burnout of muscles, consumption of excess protein supplements or cooked meat. 

Low levels of creatinine show a decrease in muscle mass. 

How is the KFT test carried out?

There are two steps to complete a KFT test collection. 

  • Urinalysis: 

Urinalysis is used to check the levels of protein and the presence of blood in the urine. Urine is collected by the patient over 24 hours in a special container provided by the laboratory or hospital. This sample is then tested by the laboratory to check how fast creatinine is cleared from the body. Although there might be higher levels of creatinine in the urine for various reasons, this test is quite an accurate representation of the rate of creatinine clearance. 

  • Blood Samples:

The second step in a KFT test is the collection of the blood sample. The technician first wraps a tourniquet on the upper part of the arm to expose the veins. Then he cleans the area and draws blood to take to the lab to test the blood urea nitrogen and uric acid levels. 

What are the normal ranges of the various components of the KFT test?

The normal level of urea is estimated to be between 2.5 and 7.8 mmol/L. 

The normal level of BUN is estimated to be between 7 and 20 mg/dL. 

The level of uric acid that is considered to be normal is different for males and females. For females, the levels should be between 2.4 and 6.0 mg/dL, and for males, it must be between 3.4 and 7.0 mg/dL. For children, it should be at a level between 3 and 4 mg/dL. 

The normal level of creatinine is also different for males and females. For adult males, it should be 0.6 to 1.2 mg/dL and for adult females, it must be at 0.5 to 1.1 mg/dL. 

An abnormal level of any of these parameters may be indicative of many other conditions other than health disorders. These normal levels may also vary from laboratory to laboratory. Overall, the KFT test is really useful in understanding the health of the kidneys.