Blood urea nitrogen

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Blood urea nitrogen

The blood urea nitrogen (BUN) test is a measure of the amount of nitrogen in the blood in the form of urea, and a measurement of renal function

Renal function

Renal function, in nephrology, is an indication of the state of the kidney and its role in renal physiology. Glomerular filtration rate describes the flow rate of filtered fluid through the kidney....
. Urea
Urea

Urea is an organic compound with the chemical formula 2carbonoxygen.Urea is also known by the International Nonproprietary Name carbamide, as established by the World Health Organization....
is a substance secreted by the liver

Liver

The liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, a few of which are detoxification, protein synthesis, and production of biochemicals necessary for digestion....
, and removed from the blood by the kidneys.

liver produces urea in the urea cycle

Urea cycle

The urea cycle is a cycle of biochemistry reactions occurring in many animals that produces urea 2carbonoxygen from ammonia . This cycle was the first metabolic cycle discovered ....
as a waste product of the digestion

Digestion

Digestion is the mechanical and chemical breaking down of food into smaller components, to a form that can be Absorption, for instance, by a blood stream....
of protein

Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
. Normal human adult blood should contain between 7 to 21 mg of urea nitrogen per 100 ml (7-21 mg/dL) of blood.

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Encyclopedia

The blood urea nitrogen (BUN) test is a measure of the amount of nitrogen in the blood in the form of urea, and a measurement of renal function

Renal function

Liver

Physiology

The liver produces urea in the urea cycle

Urea cycle

Digestion

Digestion is the mechanical and chemical breaking down of food into smaller components, to a form that can be Absorption, for instance, by a blood stream....
of protein

Protein

Interpretation

The most common cause of an elevated BUN, azotemia
Azotemia

Azotemia is a medical condition characterized by abnormal levels of nitrogen-containing compounds, such as urea, creatinine, various body waste compounds, and other nitrogen-rich compounds in the blood....
, is poor kidney function, although a serum creatinine

Creatinine

Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body ....
level is a somewhat more specific measure of renal
Kidney

The kidneys are Organ that have numerous biological roles. Their primary role is to maintain the homeostasis balance of bodily fluids by filtering and secreting Metabolomics#Metabolitess and minerals from the blood and excreting them, along with water , as urine....
function (see also renal function

Renal function

Renal function, in nephrology, is an indication of the state of the kidney and its role in renal physiology. Glomerular filtration rate describes the flow rate of filtered fluid through the kidney....
).

A greatly elevated BUN (>60 mg/dL) generally indicates a moderate-to-severe degree of renal failure. Impaired renal excretion of urea may be due to temporary conditions such as dehydration

Dehydration

Dehydration is the removal of water from an object. In Physiology terms, it entails a relative deficiency of water molecules in relation to other dissolved solutes....
or shock, or may be due to either acute or chronic disease of the kidneys themselves.

An elevated BUN in the setting of a relatively normal creatinine
Creatinine

Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body ....
may reflect a physiological response to a relative decrease of blood flow to the kidney (as seen in heart failure or dehydration

Dehydration

Dehydration is the removal of water from an object. In Physiology terms, it entails a relative deficiency of water molecules in relation to other dissolved solutes....
) without indicating any true injury to the kidney. However, an isolated elevation of BUN may also reflect excessive formation of urea without any compromise to the kidneys.

Increased production of urea is seen in cases of moderate or heavy bleeding in the upper gastrointestinal tract (e.g. from ulcers). The nitrogenous compounds from the blood are resorbed as they pass through the rest of the GI tract and then broken down to urea by the liver

Liver

The liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, a few of which are detoxification, protein synthesis, and production of biochemicals necessary for digestion....
. Enhanced metabolism of proteins will also increase urea production, as may be seen with high protein diets, steroid

Steroid

A steroid is a terpenoid lipid characterized by a carbon skeleton with four fused rings, generally arranged in a 6-6-6-5 fashion.Steroids vary by the functional groups attached to these rings and the oxidation state of the rings....
use, burns, or fevers.

A low BUN usually has little significance, but its causes include liver problems, malnutrition

Malnutrition

Malnutrition is a general term for a medical condition caused by an improper or inadequate diet and nutrition.According to the World Health Organization, hunger and malnutrition are the single gravest threats to the world's public health and malnutrition is by far the biggest contributor to child mortality, present in half of all cases....
(insufficient dietary protein), or excessive alcohol consumption. Overhydration from intravenous fluids can result in a low BUN. Normal changes in renal bloodflow during pregnancy

Pregnancy

Pregnancy is the carrying of one or more offspring, known as a fetus or embryo, inside the uterus of a female. In a pregnancy, there can be multiple gestations, as in the case of twins or Multiple birth....
will also lower BUN.

Urea itself is not toxic. This was demonstrated by Johnson et al. by adding large amounts of urea to the dialysate of hemodialysis

Hemodialysis

File:Plugged into dialysis.jpgIn medicine, hemodialysis is a method for removing waste products such as potassium and urea, as well as free water from the blood when the kidneys are in renal failure....
patients for several months and finding no ill effects.. However, BUN is a marker for other nitrogenous waste. Thus, when renal failure leads to a buildup of urea and other nitrogenous wastes (uremia

Uremia

Uremia is a term used to loosely describe the illness accompanying renal failure , in particular the nitrogenous waste products associated with the failure of this organ....
), an individual may suffer neurological disturbances such as altered cognitive function (encephalopathy

Encephalopathy

Encephalopathy /?n?s?f?'l?p??i/ literally means Disorder or disease of the brain. ...
), impaired taste (dysgeusia

Dysgeusia

Dysgeusia is the distortion or decrease of the sense of taste. Dysgeusia is associated with zinc deficiency and some drugs designed to treat hypertension and anxiety, including lithium....
) or loss of appetite (anorexia

Anorexia (symptom)

Anorexia is the decreased sensation of appetite. While the term in non-scientific publications is often used interchangeably with anorexia nervosa, many possible causes exist for a decreased appetite, some of which may be harmless, while others indicate a serious clinical condition, or pose a significant risk....
). The individual may also suffer from nausea and vomiting, or bleeding from dysfunctional platelets. Prolonged periods of severe uremia may result in the skin taking on a grey discolouration or even forming frank urea crystals ("uremic frost") on the skin.

Because multiple variables can interfere with the interpretation of a BUN value, GFR and creatinine clearance are more accurate markers of kidney function. Age, sex, and weight will alter the "normal" range for each individual, including race. In renal failure or chronic kidney disease (CKD), BUN will only be elevated outside "normal" when more than 60% of kidney cells are no longer functioning. Hence, more accurate measures of renal function are generally preferred to assess the clearance for purposes of medication dosing.

Units

BUN is reported as mg/dL in the United States. Elsewhere, the concentration of urea is reported as mmol/L. To convert from mg/dL of blood urea nitrogen to mmol/L of urea, divide by 2.8 (each molecule of urea having 2 nitrogens, each of molar mass 14g/mol) Urea (in mmol/L) = BUN (in mg/dL of nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
) / 2.8

convert BUN to urea in mg/dL by using following formula: Urea= BUN*2.14 MW of urea =60 urea nitrogen : 28 = 60/28

Methodology

See also: Wikibooks: wikibooks:How to make a blood urea nitrogen (BUN) test

The test as originally carried out was by flame photometry; now chemical colorimetric tests are more widely used. Three methods are common: Diacetyl Monoxime, Urograph and Modified Berthelot Enzymatic methods: