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.
Why get tested?
There is not one type of kidney disease, rather, many different conditions that can cause a reduction in kidney function.
How the kidneys work
Your kidneys are located just at the bottom of your ribcage on either side of your spine. Inside are about a million tiny blood filtering units. These filter your blood and remove wastes and excess fluid from your body, which is disposed of as urine.. If the kidneys are not working properly, waste products can build up, and the chemical balance is disturbed and the levels of sodium, potassium, phosphate and calcium are not regulated correctly. Fluid levels can increase to dangerous levels, causing damage and serious conditions.
Blood enters the kidneys where it passes through 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. Attached to the glomerulus are looping tubes, called tubules. The glomerulus filters your blood, and the tubules return what can be re-used by the body to your blood and remove wastes.
As the blood passes through the glomerulus the thin walls allow smaller molecules, wastes, and fluid to pass into the tubule. Larger molecules, including proteins such as albumin and blood cells are kept behind.
As the filtered fluid moves along inside the tubule, almost all the water, along with the minerals and nutrients your body needs are absorbed. The remaining fluid and waste materials, including excess acids, are sent to the bladder as urine.
The kidneys ensure that the make-up and volume of fluids in the body is correct and they maintain the chemical balance. They help to regulate electrolytes such as sodium, potassium, bicarbonate, chloride, phosphorus, calcium, and magnesium. Having the right balance 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.
Kidneys also have several other roles in maintaining a healthy body, including producing the hormone erythropoietin that stimulates red blood cell production, producing the hormone renin that helps maintain a normal blood pressure, and turning one form of vitamin D into a more active form, which enhances calcium absorption.
Although the tests in a kidney function panel can vary between laboratories, these tests are typically performed:
|TESTS||WHAT IS BEING MEASURED|
These are 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. They include:
|Albumin||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 calcium throughout the body.|
|Urea and creatinine (waste products)|
|Glucose||Glucose – supplies energy for the body and a steady amount must be available. A relatively constant level of glucose must be maintained in the blood.|
|Cystatin C||Cystatin C is used for detecting and monitoring the progression of kidney disease. It may be slightly more sensitive to early kidney disease as levels might rise sooner than creatinine. Cystatin C is more costly and a less available test than creatinine.|
|Estimated glomerular filtration rate (eGFR)||Estimated Glomerular Filtration Rate (eGFR) – a calculated estimate of the actual glomerular filtration rate. This is the amount of blood filtered by the glomeruli in the kidneys per minute. The calculation is based on creatinine levels in the blood and the formula takes into account a person's age, gender, race, and sometimes height and weight.|
Blood tests are often ordered together with a urinalysis. This measures levels of chemicals and proteins in your urine and checks your urine concentration and pH (acid) level. Moderately raised albumin to creatinine ratio (ACR) levels can indicate early kidney disease which is often caused by diabetes.
Having the test
Blood and urine
You may be asked to fast for 8 -12 hours (no food, only water) before the test.
Reading your test report
Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.
Kidney function test results cannot diagnose a condition and can only show if there may be a problem with your kidneys. Further testing will be required to make a diagnosis and identify the likely cause.
Results from the test panel are usually considered together. Individual test results can be abnormal due to causes other than kidney disease, but taken together with your symptoms and health history, they can provide a good overview of your kidney health.
|Concentrations of electrolytes in the blood can be affected by kidney disease in different ways depending on the cause, with some concentrations decreasing while others increase. In general, impaired kidney function or kidney disease can cause an imbalance among the electrolytes. When these positively and negatively charged ions are out of balance, it can affect the fluid balance and/or pH of the blood. As kidney function worsens, complications such as metabolic acidosis may result.|
|Phosphorous||High blood concentrations are associated with kidney disease.|
|Calcium||High blood concentrations are associated with kidney disease.|
A low blood concentration may suggest that albumin
is leaking through the kidneys into the urine and being lost.
|Urea||High levels suggest impaired kidney function caused by acute or chronic kidney disease, damage, or failure, or due to another condition causing decreased blood flow to the kidneys, such as congestive heart failure (CHF) or dehydration, or causing obstruction of urine flow, such as prostate disease or kidney stones.|
|Creatinine||High blood concentrations suggest impaired kidney function due to conditions listed for urea.|
|Glucose||High blood concentrations indicate diabetes, a common cause of kidney disease.|
|Cystatin C||A high cystatin C result indicates a low GFR (glomerular filtration rate).|
|eGFR||This is a calculation taken from the blood creatinine test result. An eGFR below 60 mL/min suggests that some kidney damage has occurred. An eGFR below 15 indicates kidney failure.|
Additional testing may be performed, such as kidney imaging or a kidney biopsy, if blood and urine testing indicate the possibility of kidney disease.
Questions to ask your doctor
The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.
You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.
Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:
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