Azotemia

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Azotemia is a medical condition characterized by abnormally high levels of nitrogen-containing compounds, such as urea, creatinine, various body waste compounds, and other nitrogen-rich compounds in the blood. It is largely related to insufficient filtering of blood by the kidneys.[1]

Contents

Types

Azotemia has three classifications, depending on its causative origin, but all three types share a few common features. All forms of azotemia are characterized by a decrease in the glomerular filtration rate (GFR) of the kidneys and increases in blood urea nitrogen (BUN) and serum creatinine concentrations. The BUN-to-creatinine ratio (BUN:Cr) is a useful measure in determining the type of azotemia. A normal BUN:Cr is less than 15.[2]

Prerenal azotemia

Prerenal azotemia is caused by a decrease in blood flow to the kidneys, which can be caused by shock, decreased cardiac output, volume depletion, narrowing of the renal artery, etc.,[2] resulting in inadequate blood supply to the kidneys. There is no inherent kidney disease. It can occur from hemorrhage, shock, volume depletion, and congestive heart failure; among other things.[1]

The BUN:Cr in prerenal azotemia is greater than 20.{http://libdb.sjfc.edu:4107/online/content/topic.do?topicKey=renlfail/10967&selectedTitle=1%7E62&source=search_result#H10} The reason for this lies in the mechanism of filtration of BUN and creatinine. GFR levels are decreased due to hypoperfusion, leading to a general greater increase in BUN than creatinine. Since the kidney is functioning correctly, the response to decreased GFR is to increase reabsorption rates. The increased reabsorption of Na leads to increased water and urea reabsorption from the proximal tubules of the kidney back into the blood. In contrast, creatinine is actually secreted in the proximal tubule. This generally leads to a BUN:Cr ratio > 20 and a fractional excretion of Na of < 1% and an elevated urine osmolarity.

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