Tests For Kidney Function: Purpose Of Kidney Diagnostic Tests

Purpose Of Kidney Diagnostic Tests
6 Jan 2022
9 mins
Table Of Content
Tests For Kidney Function: Purpose Of Kidney Diagnostic Tests

    The kidneys are vital organs that maintain a balance in fluids, electrolytes, acids and base substances. They help in the absorption of several substances crucial for the body’s development and excrete waste products. Considering these significant functions, it is vital to detect abnormalities earlier to prevent further damage to the kidneys.


    Read further to know in depth about kidney diagnostic tests, i.e., urine and blood test for kidney function, and renal tests involving imaging techniques.


    What Are The Important Tests For Kidney Function?


    Various diagnostic tests are employed to detect the status of kidney function. Generally, the kidney diagnostic tests start with routine urine examination, serum creatinine, blood urea content and eventually, the specific tests to determine the ability of your kidneys to eliminate wastes, i.e., clearance tests for kidney function. 


    1. Blood Test For Kidney Function:


    There are three important blood tests for kidney function to determine the extent of damage caused in your kidneys and predict how well your kidneys are functioning. 


    • Blood Urea:


    This blood test for kidney function determines the extent of kidney damage by assessing the amount of urea and creatinine present in your blood.

    • Serum Creatinine:


    Creatinine is an excretory product released by the muscles. It releases at a constant rate and is independent of the body’s metabolism and diet. Serum creatinine test is a more accurate blood test for kidney function than the urea test. It can vary according to an individual’s size and age. A creatinine level greater than 1.2mg/dl for women and 1.4mg/dl for men indicates that the kidneys are not working sufficiently. As the condition progresses, the level of creatinine in the blood rises.


    • Glomerular Filtration Rate:


    Approximately 1200ml of blood containing 650ml of plasma passes through the kidneys every minute. Out of this, the kidneys filter about 120-125ml per minute. This is referred to as the Glomerular Filtration Rate (GFR). This value can be estimated using your serum creatinine value. Your GFR value tells how well your kidneys are removing wastes and excess fluid from the blood.


    GFR value of 90 indicates kidney damage with normal GFR. GFR value less than 15 indicates kidney failure that requires renal replacement therapy like dialysis and kidney transplant.

    2. Urine Tests For Kidney Function:


    These are simple kidney diagnostic tests to find conditions that might require treatment, like infections or kidney problems. Urinalysis or urine tests also help detect conditions like diabetes, liver damage, and chronic kidney disease. You have to urinate in a clean cup called a specimen cup and send the sample to a laboratory for testing.

    a. Clearance Tests For Kidney Function:


    The clearance tests are the most useful kidney diagnostic tests that measure the quantity of a substance cleared by the kidney in a minute.

    • Creatinine Clearance Test:


    The kidney component called glomerulus filters creatinine and is only secreted by the tubules on trace levels. The creatinine clearance value is close to GFR; therefore, this test is sensitive and effectively determines how well the glomerulus is working. 

    Creatinine clearance is defined as the volume of blood plasma that is free of creatinine in a minute. The normal range of creatinine clearance is 120-145ml/min. Lower creatinine clearance value signifies decreased GFR value due to poorly functioning kidneys. This kidney diagnostic test effectively compares the creatinine in the 24-hour urine sample to the creatinine in the blood. This measures the amount of waste products your kidneys filter each minute. 

    • Urea Clearance Test:


    Urea is the final product of protein metabolism. After being filtered by your kidneys, it gets reabsorbed in the tubules. Urea content is influenced by dietary protein intake. Hence urea clearance test is not as strong a determining factor as the creatinine clearance test.


    Urea clearance is defined as the plasma volume in the blood that is free of urea per minute. The normal value of standard urea clearance is 54ml/min. A urea clearance value below 75% is suggestive of kidney damage.


    b. Albumin: Creatinine Ratio:


    When your kidney has abnormalities, it allows a small fraction of a protein called albumin to leak into urine. A small quantity of albumin in the urine is called microalbuminuria. In this case, the ratio has a value between 30 and 300. On the other hand, a value above 300 refers to severely increased albumin in urine, also termed as macroalbuminuria.


    c. Routine Urine Analysis:


    Your sample will be checked visually for its colour and appearance. Foam-like urine could be a sign of kidney problems. After visual examination comes the pH test. Urine with a pH above the normal range indicates the presence of kidney stones, urinary infection, kidney problems or other disorders.

    d. Protein In Urine:


    Healthy kidneys remove waste products but leave behind substances that are beneficial to your body, one of them being protein. If protein is detected in your urine, it means your kidneys are not functioning enough to filter the waste products. 

    e. Urine Culture:


    This test involves examining your urine sample under the microscope to detect the presence of infection. The presence of blood in urine indicates infection, kidney problem or heavy exercise.

    3. Other Significant Kidney Diagnostic Tests:

    • Imaging Tests (Ultrasound/ CT scan):


    Imaging tests can give a clear picture on the status of your kidney by showing the size and shape of your kidneys and urinary tract. It can also detect stones, tumours and other issues.


    An ultrasound test sends sound waves to get a picture of the kidneys. It detects abnormalities in the size and the positioning of the kidneys and also checks for the presence of stones and tumours.


    CT scan refers to an imaging method that uses X-rays to analyse the kidneys. This imaging technique detects structural abnormalities and the presence of an obstruction in the kidneys. This test needs contrast dye which could be a cause of concern for people diagnosed with kidney disease.

    •  Kidney Biopsy:


    Kidney biopsy is a renal test involving the process of extracting tiny pieces of your kidney tissues to evaluate under a microscope. Not everyone requires a kidney biopsy. A kidney biopsy can analyse the cause of your kidney problem and the extent to which your kidney is damaged.


    Know About Your Kidney By Testing:


    The only way to know about the health of your kidney is to get tested. If you are diabetic, or having high blood pressure, or a family history of kidney disease then periodic testing is very important. Kidney damage usually cannot be fixed, but can be prevented from getting worse by finding and treating kidney disease early.


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    BhairaviContent Writer
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