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Exploring the Role and Function of the Kidneys

Classifying Chronic Kidney Disease

A good indicator to determine if there is a decrease in kidney functioning is assessing the glomerular filtration rate (GFR). GFR is the volume of blood filtered by the glomerulus each minute. Normal GFR is within the limits of 120-125ml/min. If your GFR is <60mL/min, it is a primary indicator of impaired renal functioning.  In comparison, kidney failure is defined as a GFR of <15 mL/min.

Renal function tests use measurements of GFR to provide information on kidney function. Such tests are called clearance tests which determine the amount of blood cleared by a particular substance. Healthcare professionals may determine renal function by reviewing:


Classifying Chronic Kidney Disease

A 24-hour urine collection involves the patient collecting all of their urine in a container for a 24-hour period. A urine collection, allows a healthcare professional to examine whether there was an increase or decrease in urine output, which may indicate renal impairment.  Increased urine volume may indicate kidney dysfunction, as the ability to concentrate urine is lost. Decrease in urine output may indicate kidney obstruction or renal failure.

24 hour Urinary Output


Polyuria (production of large amounts of urine)


Normal adult

1500 ml/day

Oliguria (production of small amounts of urine)

<500 ml/day

Anuria (failure of kidneys to produce urine)



Creatinine filters in the glomerulus but is not reabsorbed back into the blood. In healthy kidneys, serum creatinine levels remain around 120ml/min and stays fairly constant. When our kidney’s ability to filter our blood is impaired, creatinine levels are elevated in the body.

‚ÄčAlbuminuria also known as proteinuria is the abnormal loss of albumin or blood proteins found in the urine. This occurs when the glomerulus in our nephrons become damaged. As a result, proteins that are in our blood tend to leak into our urine. Therefore it is used as the earliest marker for glomerular disease. It is associated with hypertension, obesity, and vascular disease that damage our kidney’s ability to filter blood appropriately.  How we assess proteinuria is through a measurement called a urine- to-creatinine ratio (UACR). If the urine sample contains more than 30 mg or every gram of creatinine (30mg/g), this is an indication of a kidney problem.

Signs of proteinuria:

  • Urine looks foamy in the toilet
  • Swelling in the hands, abdomen, legs, and feet. This symptom is called edema. Proteins create an oncotic pull that draws water into the blood. When protein is lost in our urine, this function is lost and water accumulates in our extremities.