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Kidney Function Tests

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What are Kidney Function Tests?

Kidney Function tests are a battery of blood and urine tests designed to measure the efficiency of the kidneys. The main functions of the kidneys are to filter out waste products, regulate the level of essential salts along with water in the body. Therefore, the rising levels of these products are a clear indication of how well the kidneys are performing. Besides this, it stimulates the production of red blood cells, regulates blood pressure and activates Vitamin D.

Normally, these tests consist of the following:

  • The first test that is carried out when kidney disease is suspected is a urine test that checks for protein or albumin in the urine.
  • Besides this blood tests that measure blood urea nitrogen, creatinine, estimated glomerular filtration rate and levels of various electrolytes are carried out.
  • A creatinine clearance test measures how much creatinine is cleared by the kidneys in a minute.

Why is it conducted?

The initial stages of kidney disease do not produce any noticeable symptoms. Generally these become obvious only when considerable irreversible damage has set in.

  • The purpose is to check whether any condition within the body has affected the functioning of the kidneys. If detected in the early stage, kidney damage can be considerably slowed or even reversed.  
  • They help to understand the extent of damage and to grade it from grade 1 to grade 5 for better clinical understanding.
  • Besides this, these tests can be used for follow up and to regulate treatment for chronic kidney disease (CKD).
  • These tests can help to gauge the need for dialysis to clear toxins from the body.

Who should go for it?

  • People with longstanding uncontrolled diabetes, hypertension or heart disease may be advised to undergo a kidney function test.
  • Some medicines, like nonsteroidal anti-inflammatory such as ibuprofen, are known to cause damage to the kidneys and persons who consume these regularly are advised this test to check for damage.
  • Persons who have noticeable swelling in hands and lower legs.
  • People who see blood in their urine may be ordered these tests if other symptoms point towards renal insufficiency.


A sample of urine is taken to check for albumin in the urine. For the blood tests, blood will be drawn from the vein. However, if you are having a creatinine clearance test, then all urine passed out within 24 hours is collected by the patient in the given container and brought in for testing.

Interpretation of results

  • Urine albumin: This should be below 30mg/L.
  • Blood Urea Nitrogen (BUN): The normal ranges for blood urea 6 to 20 mg/dL . an increase can be caused due to other factors also.
  • Creatinine: The normal range for a creatinine blood test is from .6 to 1.2 mg/dL.
  • Estimated glomerular filtration rate (eGFR): In the initial stage of kidney damage, this may be higher than 60 which is considered to be normal. GFR is always interpreted in relation to age as well as gender, as it falls with age. This can help to detect renal insufficiency only after 60% damage has already been done to the kidneys.
  • Creatinine clearance test: In this a comparison between blood creatinine and urine creatinine is made. Normal ranges for men are between 85 - 125 ml/min and or women 75-115ml/min.
  • Dissolved salts/electrolytes: sodium, potassium, bicarbonate and chloride: The kidneys maintain a fine balance of essential salts within the body for optimal functioning. Normal ranges for sodium are  135 - 145 mmol/L, potassium 3.5 - 5.0 mmol/L, bicarbonate 22-30 mmol/L and chloride 98 – 108 mmol/L

Written by: Nandita tripati

Date last updated: January 09, 2015