BUN:serum creatinine ratio in acute tubular necrosis

[Oh_Gee]

both pathoma (pg 126, 2017) and first aid (pg 571, 2017) say acute tubular necrosis will have BUN:Cr < 15 b/c the damaged tubular epithelium can't reabsorb BUN like in normal physiology.

i'm confused b/c if ATN results in blockage of the tubules, BUN can't even get into the tubules. So why would it matter that it can't be reabsorbed?

Uptodate says "BUN/serum creatinine ratio is normal at 10 to 15:1 in ATN" (Etiology and diagnosis of prerenal disease and acute tubular necrosis in acute kidney injury in adults)

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[ASM student]

So why would it matter that it can't be reabsorbed?
It didn't matter, BUN:creat ratio is normal in ATN, they both rise but with the normal ratio maintained.

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[Oh_Gee]

So why would it matter that it can't be reabsorbed?
It didn't matter, BUN:creat ratio is normal in ATN, they both rise but with the normal ratio maintained.

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so first aid and pathoma are wrong and uptodate is right?

also of note, robbins pathology does't mention creatine but it does say BUN rises

 

[68PGunner]

both pathoma (pg 126, 2017) and first aid (pg 571, 2017) say acute tubular necrosis will have BUN:Cr < 15 b/c the damaged tubular epithelium can't reabsorb BUN like in normal physiology.

i'm confused b/c if ATN results in blockage of the tubules, BUN can't even get into the tubules. So why would it matter that it can't be reabsorbed?

Uptodate says "BUN/serum creatinine ratio is normal at 10 to 15:1 in ATN" (Etiology and diagnosis of prerenal disease and acute tubular necrosis in acute kidney injury in adults)

Alright, dude. Blockage of the tubule will decrease the filtration of both BUN and Cr, so the ratio will stay at 15, above, or whatever normal is. But, you will see an elevated BUN or Cr level from your baseline for each of these components.


However, in acute tubular necrosis, BUN reabsorption will be less due to the damage in the tubules; Cr doesn't get reabsorbed in the tubules. Therefore you might start to see the BUN:Cr ratio gradually decreasing from the normal baseline. In this last scenario, BUN and Cr serum conc will individually be elevated from the baseline. This is the case for pre renal, intra-renal, and post renal problems.

 

[ASM student]

so first aid and pathoma are wrong and uptodate is right?

also of note, robbins pathology does't mention creatine but it does say BUN rises

No one is wrong, they're all saying the same thing, the normal BUN:Creat ratio is < 15 which will be maintained in ATN.

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