What is kidney function test- types, purpose & procedure?

What are the kidney function tests?

Kidney function test (KFT) is a broad term used for a group of certain tests, which are done to evaluate the overall functioning of the kidneys. To understand how efficiently the kidneys are doing their job of eliminating waste from the body. The natural filtration system of the body performs many important functions like removing metabolic waste from the bloodstream, water balance regulation in the body, and maintains the pH level of the body fluids. A nephrologist understands the kidney functioning in the best possible way so he must be consulted in case of any kidney problems.

kidney function

Both the kidneys are placed on either side of the spine below the rib cage being approximately of human fist size. Their min vital job is to eliminate excess water in the form of urine from the body. They also control the water levels and minerals in the body. Further, they play an essential role in the production of several hormones which regulates many body essentials like the most important one is blood pressure.

Need for kidney function test arises whenever the physician of patient thinks that the kidneys are not properly working. Doctors recommend the kidney test over the time to observe the impact of diseases like diabetes and high blood pressure on a kidney.

Different types of this tests?

The main tests include: urine and blood analysis tests

Urine analysis tests

  • Creatinine test:

    In this test, it becomes evident how efficient the kidneys are in removing creatinine from the blood. Creatinine is a waste metabolic product of muscle energy. Within few days, the whole filtration process of creatinine excretion is done by kidney through urine. Due to which its clearance from blood becomes an important task for kidney and its proper functioning. A urine sample is collected over 24 hours prior the test is performed. In order to calculate the urine clearance blood creatinine levels are also required. Creatinine albumin ratio in urine must also be calculated. This is one of the main tests of urinalysis.

  • Urea test:

    Urea is a byproduct of the protein metabolism, excretion in the urine is indeed. The clearance test of urea requires a blood sample to calculate the actual amount of urea in the main bloodstream. The filtering or eliminating process of the kidney into the urine,  this two urine sample collection is done in a difference of nearly one hour.

  • Osmolality test:

    It is a measurement of a number of dissolved particles in the urine. It is more precise to calculate osmolality rather than the specific gravity for evaluating kidney ability to concentrate or dilute the urine. If fluid intake is increased then kidneys are supposed to excrete more water into the urine and if fluid intake is decreased kidneys will excrete less water in urine making it concentrated. Urine sample for the test is collected as a first urine of the day and a cumulative sample is collected over a 24 hour period. High protein diet and no fluid intake at night recommended few days prior the test is conducted.

  • Urine protein test:

    Kidneys filter all proteins from the main bloodstream and reabsorb them, as doctors recommend very low protein in urine. Excess protein levels in urine sample indicate malfunctioning of the kidney. If screen test for protein comes out to be positive in urinalysis. Then later for more precise results, a random urine sample is followed up with a 24-hour urine sample.

Blood Analysis

  • Serum creatinine test: This blood test determines creatinine build up in the blood. The kidneys clear entire creatinine from the blood by filtration. The presence of an increased level of creatinine in the blood indicates a kidney problem. A creatinine value – 1.2 milligrams/deciliter (mg/dL) for women and 1.4 mg/dL for men indicates kidney problems.

kidney function

  • Blood urea nitrogen: The evaluates all waste metabolic byproducts like blood urea nitrogen (BUN) in the blood is done. It measures nitrogen amount in the blood. Urea nitrogen is a byproduct of protein. However, the elevated level of the BUN is not the only way to indicate kidney damage. Certain analgesic medications, which even include aspirin high doses and few antibiotics, also cause an increase in BUN values. Share all medication history with your physician to avoid false results before the test. Doctor recommend the normal level of the BUN, between 7 and 20 mg/DLA. A higher value then this might indicate kidney problems.
  •       Estimated GFR:  This test helps in estimating how efficiently the kidneys filter waste from the blood. It further depends on factors like height, weight, age, gender, race of the patient and test results of creatinine. Results of EGFR less than 60 milliliters/minute/1.73m2 indicates kidney disease.

Normal test values for many tests evaluated based on the patient’s age, and gender is as follows:

Urine tests

  • Creatinine clearance: For a 24-hour urine sample collection, its normal results must be 90 mL/min–139 mL/min for males<40, and 80–125 mL/min for females<40, above 40 the values decrease by 6.5 mL/min per decade of life.
  • Urine osmolality: With limited fluid intake for concentration testing the osmolality must be >800 mOsm/kg of water. However with increased intake for dilution testing the osmolality must<100 mOSm/kg in at least one specimen, 24-hour urine osmolality must be between 300–900 mOsm/kg upon an average, random urine osmolality must be between 500–800 mOsm/kg upon an average.
  • Urine protein: In a 24-hour urine sample it must contain<150 mg of protein.
  • Urine sodium: In a 24-hour urine sample sodium must be between 75–200 mmol/day.

Blood tests

  • Blood urea nitrogen (BUN) must be between 8–20 mg/dL upon an average.
  • Creatinine must be between 0.8–1.2 mg/dL for the males, and 0.6–0.9 mg/dL for the females.
  • Uric acid levels for the males must be between 3.5–7.2 mg/dL and for the females 2.6–6.0 mg/dL.

Other tests include:

  • Complete blood analysis for electrolyte presence in the blood like sodium, potassium, chloride, and bicarbonate.
  • A complete blood count test.

What is the purpose of kidney function test?

  • Kidney tests are very important especially for people who have any underlying diseases like diabetes, blood pressure or any cardiac problems. Such diseases leave an impact on the renal system over the time.
  • Evaluate the presence of all electrolytes in the blood.
  • KFT monitoring evaluate the impacts of excess intake of few harmful medications on kidney
  • In case of the pre-existing kidney, disease tests are necessary to monitor the condition.
  • To prevent any abnormal levels of creatinine, urea or electrolytes worsen kidney condition, understanding kidney test results becomes very important. One should follow a healthy after knowing the results.
  • Few symptoms including abnormal urine, painful or frequent urination, edema, and difficulty in urination might require kidney function test to evaluate and diagnose the main cause.

Explain the procedures for this test?

Kidney function tests normally require a 24-hour urine sample along with a blood sample for the blood test.

24-hour urine sample

A 24-hour urine sample test is a creatinine clearance test. It evaluates the expulsion of creatinine by the body in a single day. The person has to pass first urine normally like any other day, on the day 1 when the test starts. For the rest of the days and even nights, collect urine in a special container for the test. Properly label it and store separately. The 24-hour urine sample collection process then completes on the day 2 first morning urine collection in the same sample. The physician, then collect sample deposited back for the analysis.

Blood sample collection

For BUN and serum creatinine tests blood samples are taken in a lab by the lab technician or in the office of the physician.

kidney function

The technician first tie an elastic band around the upper arm, making the veins visibly appears and clean the entire area, before drawing the blood, and the insert the hollow needle to take blood, the sample is then, sent for test analysis.

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