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Blood urea nitrogen (BUN) is a medical test that measures the amount of urea nitrogen found in blood. The liver produces urea in the urea cycle as a waste product of the digestion of protein . Normal human adult blood should contain 7 to 18 mg/dL (0.388 to 1 mmol/L) of urea nitrogen. [ 1 ]
In medicine, the urea-to-creatinine ratio (UCR [1]), known in the United States as BUN-to-creatinine ratio, is the ratio of the blood levels of urea (mmol/L) and creatinine (Cr) (μmol/L). BUN only reflects the nitrogen content of urea (MW 28) and urea measurement reflects the whole of the molecule (MW 60), urea is just over twice BUN (60/28 ...
Blood urea nitrogen (BUN) - Also measured using a BMP or CMP, blood urea nitrogen is an indicator of how much nitrogen is in the blood at the time of the phlebotomy. The kidney is responsible for excreting nitrogenous substances in the urine, so an elevated BUN usually indicates that the kidney is not functioning appropriately.
In 1851, E.T. Frerich described clinical uremic syndrome and suggested that a toxicity was the mechanism of its cause. It was in 1856 that J. Picard developed a sensitive method to reproducibly measure blood urea. He was able to detect a 40% decrease of urea concentration between the renal artery and the renal vein.
Measurements of urea and creatinine (Cr) in the blood are used to assess renal function. For historical reasons, the lab test measuring urea is known as "blood urea nitrogen" (BUN) in the US. The BUN:Cr ratio is a useful measure in determining the type of azotemia and will be discussed in each section below.
Outside the United States, blood tests made up of the majority of the same biochemical tests are called urea and electrolytes (U&E or "U and Es"), or urea, electrolytes, creatinine (UEC or EUC or CUE), and are often referred to as 'kidney function tests' as they also include a calculated estimated glomerular filtration rate. The BMP provides ...
An alternative estimation of kidney function can be made when interpreting the blood plasma concentration of creatinine along with that of urea. BUN-to-creatinine ratio (the ratio of blood urea nitrogen to creatinine) can indicate other problems besides those intrinsic to the kidney; for example, a urea concentration raised out of proportion to ...
The functions of the kidney include maintenance of acid-base balance; regulation of fluid balance; regulation of sodium, potassium, and other electrolytes; clearance of toxins; absorption of glucose, amino acids, and other small molecules; regulation of blood pressure; production of various hormones, such as erythropoietin; and activation of vitamin D.