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 Correct normal BUN/creatinine ration  

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Hi there,

Heard that Goljan said 10/1 is normal, then I read Qbank says 12-20 to 1--who is correct?

Thank you.


One more thing--why would liver dz cause low BUN/creatinine? I thought the liver partially breaks down urea--isn't that how you get the hand-flapping in cirrhosis patients (astigymus? or some such name)? Or was that ammonia?? If ammonia, doesn't urea and ammonia share some biochem transofmative reaction?? ARRRRRRRRRRRRRRGGGGGGGGGGGGGGGGGGG!!!


You'd think (or at least I would) that with a failing kidney, you'd increase your BUN/creatine. I am quoting this stuff straight from Qbank (that devil's tool)


Continuing to reply to myself then: so is it because you don't reabsorb urea in ATN that the BUN/creatinine ratio drops off? But then, you must filter the urea through first for it to get into the tubule and not be reabsorbed--and I thought the kidney wasn't filtering or reabsorbing or functioning period in ATN.

G-d damn it!!!!!!!!!!!!! :evil: :evil: :evil: :evil: :evil: :evil: :evil: :evil:


ATN affects the tubules, and the glomerulus still remains intact. The BUN/creatinine ratio should drop due to a lack of reabsorption of urea, like you said.

In liver failure, urea production is decreased (remember that the urea cycle occurs in the liver). Ammonia builds up in cirrhotic patients since the ammonia is not used for urea production (the ammonia is formed from deamination).


Thanks for saving my sanity Sakaki--and I think the word I was looking for was "asterixises" sp?? :wink:

Following on the BUN/creatinine in CHF and bleeding, then (I think mdwannabe tried to help me on this earlier, but I want to see if I understood by trying to reason this out correctly here), will you increase reabsorbtion of things including urea through the tubules, and thereby increase the BUN/creatinine ratio?

Also, in ARF & CRF (acute and chronic renal failure)--will BOTH the glomerulus not filter and the tubules not reabsorb, or what? My guess is that the glomerulus will not filter and the tubules will not reabsorb.. so the BUN/creatinine should stay in the same proportions just rising.

Anyone up for a critique of my reasoning/answers? Please do!

Thank you!


Yes, the BUN:creatinine ratio rises in CHF. The urea would rise due to decreased renal plasma flow (prerenal azotemia), and it is likely that creatinine would rise too, but not as fast as urea.

In ARF and CRF, it is obvious that GFR decreases. At the same time, urea reabsorption is increased at low urine flow rates (ref. Schrier's Atlas of the Kidney .... or something like that, and it states that the reason is unknown). In either case, the net result is that BUN:creatinine ratio rises in ARF and CRF.


The normal BUN/creat ratio is 10-15:1. once its more than 20:1 then it is considered to be a pre-renal disease(unless there are other things going on)

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