Attached to each glomerulus is a tiny tube (tubule) that collects the fluid and molecules that pass through the glomerulus and then reabsorbs what still can be used by the body. The glomerulus allows the passage of water and small molecules but retains blood cells and larger molecules. In each nephron, blood is continually filtered through a microscopic cluster of looping blood vessels, called glomerulus. Within them are about a million tiny blood filtering units called nephrons. The kidneys are a pair of bean-shaped organs that are located at the bottom of the ribcage in the right and left sides of the back. However, when the kidneys cannot filter wastes out of the blood due to disease or damage, then the level of urea in the blood will rise. Since this is an ongoing process, there is usually a small but stable amount of urea nitrogen in the blood. Urea is formed in and released by the liver into the blood and is carried to the kidneys, where it is filtered out of the blood and released into the urine. Urea and urea nitrogen are referred to somewhat interchangeably because urea contains nitrogen and because urea/urea nitrogen is the 'transport method' used by the body to rid itself of excess nitrogen. Nitrogen is a component of both ammonia and urea. Sometimes, a BUN to creatinine ratio is calculated to help determine the cause of elevated levels. This test measures the blood urea nitrogen (BUN) level in the blood.

This process produces ammonia, which is then converted into the less toxic waste product urea. Urea is a waste product formed in the liver when protein is metabolized into its component parts (amino acids). The GFR estimates the percentage of kidney function you have left. To do this, you may have a blood sample taken to calculate your estimated glomerular filtration rate (GFR). Your doctor may also test how well your kidneys are removing waste from the blood. High levels of creatinine in your blood may be a sign of kidney damage. If kidney problems are the main concern, the creatinine levels in your blood will likely also be measured when your blood is tested for urea nitrogen levels.Ĭreatinine is another waste product that healthy kidneys filter out of your body through urine. To help determine the effectiveness of dialysis treatment if you're receiving hemodialysis or peritoneal dialysisĪs part of a blood test group to help diagnose a number of other conditions, such as liver damage, urinary tract obstruction, congestive heart failure or gastrointestinal bleeding - although an abnormal BUN test result alone doesn't confirm any of these conditions. If your kidney function needs to be evaluated If your doctor suspects that you have kidney damage The filtered waste products leave your body through urine.Ī BUN test can reveal whether your urea nitrogen levels are higher than normal, suggesting that your kidneys or liver may not be working properly. Healthy kidneys filter urea and remove other waste products from your blood. The urea travels from your liver to your kidneys through your bloodstream. The nitrogen combines with other elements, such as carbon, hydrogen and oxygen, to form urea, which is a chemical waste product. Your liver produces ammonia - which contains nitrogen - after it breaks down proteins used by your body's cells. Here's how your body typically forms and gets rid of urea nitrogen: A BUN test measures the amount of urea nitrogen that's in your blood.

A common blood test, the blood urea nitrogen (BUN) test reveals important information about how well your kidneys and liver are working.

Normal bun blood range