The kidney function tests are a group of tests performed to assess how well your kidneys are working. They measure levels of various substances, including several minerals, electrolytes, proteins, and glucose in the blood. They can be used as part of general health screening, for someone who is at risk of developing kidney disease, or to monitor someone who has been diagnosed with reduced kidney function or kidney disease.

What is being tested?

A kidney function panel is a group of tests that may be performed together to evaluate kidney (renal) function. The tests measure levels of various substances, including several minerals, electrolytes, proteins, and glucose (sugar), in the blood to determine the current health of your kidneys.

The kidneys are a pair of bean-shaped organs located at the bottom of the ribcage to the right and left of the spine. They are part of the urinary tract and perform a few essential roles and functions within the body.

• Within the kidneys are about a million tiny blood filtering units called nephrons. In each nephron, blood is continually filtered through a cluster of looping blood vessels, called a glomerulus, which allows the passage of water and small molecules but retains blood cells, proteins such as albumin, and larger molecules.
• Attached to each glomerulus are tubes (tubules) that have a number of sections that collect the fluid and molecules that pass through the glomerulus, reabsorb what can be re-used by the body, add other molecules through a process called secretion and, finally, adjust the amount of water that is eventually eliminated along with the waste as urine.
• Besides eliminating wastes and helping to regulate the amount of water in the body, these activities allow the kidneys to maintain normal chemical balance in the body. Among the important substances the kidneys help to regulate are sodium, potassium, chloride, bicarbonate, calcium, phosphorus, and magnesium. The right balance of these substances is critical. When the kidneys are not working properly, the concentrations of these substances in the blood may be abnormal and waste products and fluid may build up to dangerous levels in the blood, creating a life-threatening situation.
• Kidneys also have a number of other miscellaneous roles in maintaining a healthy body, including the production of a hormone that stimulates red blood cell production (called erythropoietin), production of a hormone that helps maintain a normal blood pressure (called renin), and turning one form of vitamin D into a more active form, which enhances calcium absorption.

If the kidneys are not functioning properly, waste products can accumulate in the blood and fluid levels can increase to dangerous volumes, causing damage to the body or a potentially life-threatening situation. Numerous conditions and diseases can result in damage to the kidneys. The most common causes of and main risk factors for kidney disease are diabetes and hypertension. 

The individual tests included in a kidney function panel can vary by laboratory, but the tests typically performed include:

Electrolytes – electrically charged chemicals that are vital to normal body processes, such as nerve and muscle function; among other things, they help regulate the amount of fluid in the body and maintain the acid-base balance. Electrolytes include:

• Sodium
• Potassium
• Chloride
• Bicarbonate (Total CO2)

Minerals

• Phosphorus – a mineral that is vital for energy production, muscle and nerve function, and bone growth; it also plays an important role as a buffer, helping to maintain the body's acid-base balance.
• Calcium – one of the most important minerals in the body; it essential for the proper functioning of muscles, nerves, and the heart and is required in blood clotting and in the formation of bones.
   

Protein

• Albumin – a protein that makes up about 60% of protein in the blood and has many roles such as keeping fluid from leaking out of blood vessels and transporting hormones, vitamins, drugs, and ions like calcium throughout the body.

Waste products

• Urea – urea is a nitrogen-containing waste product that forms from the metabolism of protein; it is released by the liver into the blood and is carried to the kidneys, where it is filtered out of the blood and eliminated in the urine.
• Creatinine – another waste product that is produced by the body's muscles; almost all creatinine is eliminated by the kidneys.

Energy Source

• Glucose – supplies energy for the body; a steady amount must be available for use, and a relatively constant level of glucose must be maintained in the blood.

A calculated value may also be reported with a kidney function panel:

• Estimated Glomerular Filtration Rate (eGFR) – a calculated estimate of the actual glomerular filtration rate (GFR, the amount of blood filtered by the glomeruli in the kidneys per minute) derived from creatinine levels in the blood; the formula takes into account the person's age, gender, race, and sometimes height and weight.

How is it used?

A kidney function panel may be used to evaluate kidney function, to help diagnose kidney-related disorders, to screen those who may be at risk of developing kidney disease or to monitor someone who has been diagnosed with kidney disease.

When is it requested?

A healthcare practitioner may order a kidney function panel when someone has signs and symptoms of kidney disease, though early kidney disease often does not cause any noticeable symptoms. It may be initially detected through routine blood or urine testing. Examples of some signs and symptoms include:

• Swelling or puffiness, especially around the eyes or in the face, wrists, stomach, thighs or ankles
• Urine that is foamy, bloody, or coffee-coloured
• A decrease in the amount of urine
• Problems urinating, such as a burning feeling or abnormal discharge during urination, or a change in the frequency of urination, especially at night
• Mid-back pain, below the ribs, near where the kidneys are located

A kidney function panel may also be ordered at regular intervals when someone is being treated for kidney disease for monitoring purposes.

What does the result mean?

Kidney function panel test results are not diagnostic but rather indicate that there may be a problem with the kidneys and that further testing is required to make a diagnosis and determine the cause. Results of the panel are usually considered together, rather than separately. Individual test result can be abnormal due to causes other than kidney disease, but taken together with risks and/or signs and symptoms, they may give an indication of whether kidney disease is present.

The following table summarises what results might mean in relation to kidney.

Is there anything else I should know?

Additional testing may be performed, such as kidney imaging or a kidney biopsy, if blood and urine testing indicate the possibility of kidney disease. 

More information

Healthdirect Australia: Kidney function tests