Kidney Function Test

A kidney function test is done to determine if you have kidney disease. Chronic kidney disease often does not have any significant symptoms until it goes in an advanced stage, which is often associated with other conditions, such as diabetes or cardiovascular disease. To catch it early and get proper treatment, consult your doctor about checking on your kidney function.

When Do You Need a Kidney Function Test?

Routine blood tests may include a kidney function test, which is a common procedure that is done:

When you want a general assessment of your health.
When you suspect dehydration and your urea levels increase.
When you are suspected to have kidney failure. High blood levels of creatinine and urea suggest that your kidneys are not working optimally. Blood creatinine levels serve as a marker of kidney function, and high levels indicate that the kidneys may be failing. This may suggest that you need dialysis treatment if creatinine levels reach a critical value.
When you want to make sure your kidneys are working properly before and after treatment with certain medications. Some medicines can cause kidney damage and it is important to check their function before and after therapy.

Routine Kidney Function Test: Blood Tests

To check if your kidneys are working properly, there are several kidney function tests that may be used in clinical practice. Among all the types, blood tests are often used as a routine test.

1. Serum Creatinine

This measures creatinine in the serum or blood, which is a waste product of normal metabolism. The amount of creatinine in the blood varies depending on various factors, such as age and size of your body. When elevated, it indicates an early sign of kidney dysfunction.

Normal range: 0.8 to 1.4 mg/dl (milligrams per deciliter). If creatinine level is greater than 1.2 mg/dl for women or 1.4 mg/dl for men, kidney disease may be suspected.

2. Glomerular Filtration Rate (GFR)

To measure how well your kidneys are removing waste and excess fluid from your blood, GFR is calculated using serum creatinine levels, your age, body size andweight.

Normal range: Normal GFR is 90 and above, with zero or little protein in the urine. A GFR value below 60 indicates that your kidneys are not working well. If below 15, kidney failure has set in.

3. Blood Urea Nitrogen (BUN)

After the body breaks down the protein from the foods you eat, urea nitrogen is produced (a waste product). If elevated, reduced kidney function is suspected.

Normal BUN range: 7 to 20mg/dl.

Other Kidney Function Tests

Although blood tests are routine tests, there’re often other kidney function tests that are required and performed by doctors to help make diagnosis and confirm your kidney function’s results, which include the following.

1. Urine Tests

Type of Urine Test	How It Works
Urinalysis	This includes a dipstick test and microscopic examination of your urine sample. The dipstick test examines the color and other characteristics of the urine, while microscopic analysis can detect other abnormalities such the presence of protein, blood, bacteria, pus and sugar. This test is used to screen for a variety of kidney and other disorders, including chronic kidney disease, urinary tract infection, kidney stones and diabetes.
Urine Protein	To determine the presence of excess amounts of protein in your urine (proteinuria), a dipstick test is done. A positive result (1+ or greater) suggests the need for an albumin-specific test or a quantitative test (albumin-to-creatinine ratio).
Microalbuminuria	This is a more sensitive test which can detect tiny amounts of protein, known as album, in in the urine. People who are at risk of developing kidney disease, diabetes and high blood pressure need to take this test if your standard dipstick test for protein is negative.
Creatinine Clearance	This test compares the creatinine level in your blood with that found in a 24-hour sample of your urine. It shows how much blood your kidneys are filtering out per minute. Normal range: 97 to 137 ml per minute in men and 88 to 128 ml per minute in women.

2. Imaging Tests

Ultrasound. This imaging test uses sound waves to obtain a picture of your kidneys. It can detect abnormalities in size, position and obstructions in the kidneys, including stones and tumors.
CT Scan. This technique takes a picture of the kidneys by using contrast dyes. It can detect structural abnormalities as well as obstructions in the kidneys.

3. Kidney Biopsy

A kidney biopsy involves taking a small tissue sample from the kidney by a small but sharp needle. The tissue is examined by a microscope to:

Identify abnormalities in the kidney
Evaluate the extent of kidney damage
Check why a transplanted kidney may not be functioning well

Important Note: Your results of a kidney function test could be affected by many medications and thus your doctor will ask you to stop taking certain medicines temporarily. However, it's not wise to stop taking your medicatins before talking to your doctor.