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Old 06-28-2012
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Help Renal Pathology

Can someone help me explain a little bit why, in renal azotemia, BUN:Cr <=15? More clearly, how to understand that there is the extrarenal loss of urea?

All kinds of discussion here are welcomed! Let's make progress together!

Thanks a lot!
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Old 06-28-2012
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serum BUN :creatinine (Cr) ratio
Cr is filtered and is neither reabsorbed nor secreted ,urea is filtered and partly reabsorbed.BUN:Cr normal ratio is 15.azotemia refers to an increase in serum BUN and Cr.there are prerenal,renal and postrenal azotemia
prerenal azotemia
BUN: Cr ratio 15
caused by a decrease in cardiac output -hypoperfusion of the kidneys decreases GFR-causes creatinine and urea to back up in blood,ratio remains unchanged ,because of proportionate increase.after filtration proportionately more urea is reabsorbed into the blood due to PoPh.all creatinine is excreted in the urine .proportionately more urea in blood increases ratio to 15
renal azotemia
BUN:Cr ratio 15
caused by parenchymal damage to the kidneys ,decreased GFR causes Cr and urea to back up in blood,increased extrarenal loss of urea.ratio is already 15.after filtration both urea and creatinine are lost in the urine ,ratio remains 15.
postrenal azotemia
BUN:Cr ratio 15
caused by urinary tract obstruction below the kidneys ,obstruction to urine flow decreases GFR-back up urea and Cr in the blood-proportionate increase at this poin,ratio unchanged .increased tubular pressure causes back -diffusion of urea not Cr into blood-disproportionate increase in urea increases ratio to 15
persistent obstruction damages tubular epithelium causing renal azotemia ,ratio 15 .postrenal azotemia :initially ratio 15,if obstruction persists- ratio 15

Last edited by irakly; 06-28-2012 at 09:11 PM.
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Quote:
Originally Posted by belindalimm View Post
Can someone help me explain a little bit why, in renal azotemia, BUN:Cr <=15? More clearly, how to understand that there is the extrarenal loss of urea?

All kinds of discussion here are welcomed! Let's make progress together!

Thanks a lot!
in renal azotemia Dysfunctional tubular epithelium results in decreased reabsorption of BUN (serum
BUN:Cr ratio < 15)
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Quote:
Originally Posted by irakly View Post
in renal azotemia Dysfunctional tubular epithelium results in decreased reabsorption of BUN (serum
BUN:Cr ratio < 15)
In renal azotemia, what is the extrarenal loss of urea? Does it mean the less reabsorption of urea from tubule due to tubular epithelium necrosis?
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Quote:
Originally Posted by belindalimm View Post
In renal azotemia, what is the extrarenal loss of urea? Does it mean the less reabsorption of urea from tubule due to tubular epithelium necrosis?
if u have goljan rr see p 393, fig 19-1c
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Quote:
Originally Posted by belindalimm View Post
In renal azotemia, what is the extrarenal loss of urea? Does it mean the less reabsorption of urea from tubule due to tubular epithelium necrosis?
before glomerulus ratio is already less than 15 because extrarenal loss of urea by skin ,GI, no reabsorbtion due to tubular damage so ratio remains less than 15
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