Postrenal Azotemia, pathoma vs F Aid

[anbuitachi]

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So in pathoma it says for post renal azotemia

Long standing obstruction is BUN/CR<15, FENA is>2%, and urine osm is <500


For First aid, they didn't mention initial or long standing, and just wrote
Postrenal: urine <350, FeNa>2%, and BUN/Cr >15.

These two sources seem to contradict. one says greater than 15, other less than 15.

Can someone explain this please? I don't see this in their errata so im assuming I'm missing something.. Thanks!

 

[Charles_Carmichael]

It depends on early vs. long-standing. Earlier on during postrenal azotemia, you don't really have tubular damage yet -- since tubular function is still intact, you're able to reabsorb BUN and have a BUN/Cr > 15, reabsorb Na+ and have a FENa < 1%, etc. As this progresses, however, you start damaging tubules and impair their function -- now they're reabsorbing less BUN and Na+, so you get a BUN/Cr < 15, FENa > 2%, etc.

So, really, it's a spectrum and depends on where you are in the disease progression. Hope that helps.

Edit: FWIW, eMedicine says that in postrenal azotemia, the BUN/Cr < 20:

http://emedicine.medscape.com/article/238545-workup

 

[anbuitachi]

It depends on early vs. long-standing. Earlier on during postrenal azotemia, you don't really have tubular damage yet -- since tubular function is still intact, you're able to reabsorb BUN and have a BUN/Cr > 15, reabsorb Na+ and have a FENa < 1%, etc. As this progresses, however, you start damaging tubules and impair their function -- now they're reabsorbing less BUN and Na+, so you get a BUN/Cr < 15, FENa > 2%, etc.

So, really, it's a spectrum and depends on where you are in the disease progression. Hope that helps.

Edit: FWIW, eMedicine says that in postrenal azotemia, the BUN/Cr < 20:

http://emedicine.medscape.com/article/238545-workup

thanks i guess i'll go w/ pathoma's early vs late, as opposed to first aids set of #s for post renal

 

[MLT2MT2DO]

thanks i guess i'll go w/ pathoma's early vs late, as opposed to first aids set of #s for post renal

If you understand what is happening you're probably better off than just memorizing. Pathoma, I felt, did an excellent job of explaining of what is going on.