Renal function test (RFT) or Kidney function test (KFT)

Renal function test (RFT) is also called kidney function test (KFT). This test is performed to check whether your kidneys are functioning normally. This is a simple test which determines the levels of various factors in blood and urine which indicates functioning of the kidney.

Kidney functions

To know details of kidney function tests, first briefly see what the function of the kidneys is. Human beings normally have two kidneys. They function normally throughout the day and night to maintain the normal body. The functions done by kidneys are as follows:

  • Maintaining the electrolyte balance of the body fluids.
  • Removing the toxic substances from the blood like urea and creatinine.
  • Maintaining the water balance of the body.
  • Kidneys also play an important role in production of Vitamin D.
  • Kidneys also produce hormones needed to produce RBCs called erythropoietin.
  • Maintaining the acid base balance of the body.

Manifestations of kidney diseases

When kidneys are unable to do their normal function some symptoms and signs are produced. These symptoms and signs can be mild to severe in intensity and may be life threatening in extreme cases.

Following are some symptoms produced by the kidney diseases:

  • Swelling of limbs especially the lower limbs.
  • Swelling of periorbital region.
  • Generalized swelling of the body.
  • Frequent or decreased urination.
  • Presence of blood in urine.
  • Rapid breathing.
  • Severe anaemia.
  • Hypo or hyperkalemia leading to heart failure.
  • Hypo or hypernatremia leading to various neurological symptoms.
  • Acidosis presenting with altered consciousness and rapid breathing.
  • Alkalosis.
  • Pain in the back of the lumbar region.
  • Pallor because of severe anaemia.
  • Frequent fractures because of decreased ability to produce Vitamin D.
  • Growth failure in children.
  • Loss of appetite.
  • Increased blood pressure is called hypertension.

If you have one or many symptoms your doctor may want to know whether your kidneys are functioning properly. 

Why to do RFT or KFT test?

We have seen the symptoms of kidney diseases in about paragraphs. This symptom may appear in some other diseases also. There are many kidney diseases with the same presentation. 

The treatment of kidney disease depends on its cause. So to find out the cause is important to do the test. The treatment and prognosis of the disease depends upon the cause of the underlying illness.

Apart from kidney diseases in many other diseases kidney function gets deranged. Patient doesn’t feel good until the renal function is restored. So even in other illnesses we need to observe the kidney function or renal function with a renal function test.

Which tests are done in a renal function test?

For the assessment of the proper functioning of the kidneys following different tests are needed.

Urine analysis

In this status freshly voided for a sample of the urine is taken. You have to collect midstream urine. From the first urination in the morning. It is collected in sterile urine containers. This sample is submitted to the lab for the test.

This sample is tested for its colour, volume, osmolarity, PH protein content and sugar content, number of RBC, WBC and epithelial cells. In urine analysis the urine sample is tested for its biochemistry and microbiology under a microscope.

Urine analysis gives an idea about protein urea that is excessive protein excretion in the urine. It also gives an idea about the presence of blood in urine measuring the red blood cells. It gives a fair idea about reasons and number of WBC cells in the urine suggesting urinary tract infection.

24 hr urine collection

Sometimes a single examination of urine analysis cannot give a fair idea about the functioning of the kidneys. In such cases 24 hour urine collection and then examination of the urine is needed. For this your doctor or lab will provide you a can to collect urine samples. 

You need to avoid the first urine of the day in the toilet. Then next time you repeat every time you need to store your urine in the provided container. You need to submit this sample to the lab after voiding the first urine of the next morning.

Blood test

Renal function tests also include blood tests. For a few ml of blood is taken from the peripheral vein. It is stored in the blood collection bulb without anticoagulant. 

After sometime the serum is formed from the blood. This serum is examined for the presence of urea, creatinine levels and also levels of sodium, potassium and chlorides.

Creatinine level more than 1.2 is considered as the presence of kidney disease and deranged kidney function. Normal range of serum creatinine level depends upon your age, sex, race, and also height and weight. 

Blood urea level may be high because of kidney disease or many other causes. Blood urea may rise because of dehydration or other drugs like antibiotics.

Maintaining the electrolyte balance is the main function of the kidneys. In acute or chronic kidney failure patient may suffer from electrolyte imbalance. Electrolyte imbalance can be detected in the form of decreased or increased sodium levels in serum for decreased or increased levels of serum potassium.

Other parameters that can be examined on blood test hemoglobin level, vitamin D level and serum erythropoietin level. But by the time this parameter side arranged renal function is so severely affected that renal failure has already been diagnosed.

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