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Encyclopedia > Blood urea nitrogen

The blood urea nitrogen (BUN) test is a measure of the amount of nitrogen in the blood that comes from urea. Urea is a substance secreted by the liver, and removed from the blood by the kidneys. Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula CON2H4 or (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Non-proprietary Names (rINN) in use in Europe. ... The liver is an organ in vertebrates, including humans. ... Kidneys viewed from behind with spine removed The kidneys are bean-shaped excretory organs in vertebrates. ...

Contents


Methodology

The test as originally carried out was by flame photometry; now chemical colorimetric tests are more widely used.


Physiology

The liver produces urea in the urea cycle as a waste product of the digestion of protein. Normal human adult blood should contain between 7 and 25 mg of urea nitrogen per 100 ml of blood. Individual laboratories may have different "usual clinical ranges", and this is because the procedure may vary. The Urea Cycle is a cycle of biochemical reactions occurring in many animal organisms that produces urea from ammonia. ... Digestion is the process whereby a biological entity processes a substance, in order to chemically convert the substance into nutrients. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... The milligram (symbol mg) is an SI unit of mass. ... The millilitre (spelled milliliter in American English and German) is a metric unit of volume that is equal to one thousandth of a litre. ...


Interpretation

The most common cause of an elevated BUN, azotemia, is due to renal failure. This can be due to a temporary condition such as dehydration or shock, or could even be a result of too much protein in the diet. Another, less common cause is a gastrointestinal hemorrhage; blood proteins are reabsorbed by the gut and modified, increasing turnover in the urea cycle. Heart attacks also raise BUN. A greatly elevated BUN (>100 mg/dl) usually indicates renal failure. Azotemia is a medical condition characterized by abnormal levels of urea, creatinine, various body waste compounds, and other nitrogen-rich compounds in the blood as a result of insufficient filtering of the blood by the kidneys. ... Renal failure is the condition where the kidneys fail to function properly. ... Dehydration is the removal of water (hydor in ancient Greek) from an object. ... In medicine, shock (hypoperfusion) is a life-threatening medical emergency characterized by inability of the body to supply enough oxygen to meet tissue requirements. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Gastrointestinal hemorrhage can be roughly divided into two clinical syndromes: upper gastrointestinal bleed, characterized by hematemesis and lower gastrointestinal bleed, characterized by melena or hematochezia. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... The Urea Cycle is a cycle of biochemical reactions occurring in many animal organisms that produces urea from ammonia. ... A myocardial infarction occurs when an atherosclerotic plaque slowly builds up in the inner lining of a coronary artery and then suddenly ruptures, totally occluding the artery and preventing blood flow downstream. ...


A low BUN usually has little significance, but its causes include liver problems, poor nutrition (insufficient protein or some vitamins), or excessive alcohol consumption. Overhydration, possibly from intravenous fluids, can also result in a low BUN. Pregnancy also lowers BUN. A pregnant woman It is the carrying of one or more embryos or foeti by female mammals, including humans, inside their bodies. ...


A serum creatinine level is a somewhat more specific measure of kidney function. Creatinine is a breakdown product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass). ... In medicine (nephrology) renal function is an indication of the state of the kidney and its role in physiology. ...


BUN, which measures urea concentration, is marker. It has little clinical significance in of itself, as urea is non-toxic. This was demonstrated by Johnson et al. by adding large amounts of urea to the dialysate of hemodialysis patients for several months and finding no ill effects.[1] This article is about clinical dialysis; for the laboratory technique, see Dialysis (biochemistry) In medicine, dialysis is a method for removing waste such as urea from the blood when the kidneys are incapable of this, i. ...


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 measured in mg/dL. To convert BUN to a urea concentration in mmol/L multiply by 0.357. Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula CON2H4 or (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Non-proprietary Names (rINN) in use in Europe. ...


See also

Kt/V - a dimensionless number used to quantify hemodialysis and peritoneal dialysis treatment adequacy. ... The urea reduction ratio (URR), is a dimensionless number used to quantify hemodialysis treatment adequacy. ... Standardized Kt/V, also std Kt/V, is a way of measuring (renal) dialysis adequacy. ...

Reference

  1. ^ Johnson WJ, Hagge WW, Wagoner RD, Dinapoli RP, Rosevear JW. Effects of urea loading in patients with far-advanced renal failure. Mayo Clin Proc. 1972 Jan;47(1):21-9. PMID 5008253

External link


  Results from FactBites:
 
Blood urea nitrogen - definition of Blood urea nitrogen in Encyclopedia (265 words)
The blood urea nitrogen (BUN) test is a measure of the amount of nitrogen in the blood that comes from urea.
Urea is a substance secreted by the liver, and removed from the blood by the kidneys.
Another, less common cause is a gastrointestinal hemorrhage; blood proteins are reabsorbed by the gut and modified, increasing turnover in the urea cycle.
  More results at FactBites »

 
 

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