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Retired NBME 22 Answers

 +17  upvote downvote
submitted by โˆ—bubbles(79)
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Chronic renal insufficiency:

1) poor phosphate clearance --> high serum inorganic phosphorous

2) high serum phosphate --> complexes with divalent cation Ca --> Ca falls

3) Ca falls --> triggers PTH axis

4) kidney failure --> decreased activity of 1-hydroxylase at the kidney --> less calcitriol

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makinallkindzofgainz  this guy renals +9
paperbackwriter  Someone please help me with this (always trips me up): PTH causes increased vit D production in kidney... are we assuming the increased PTH can't catch up with the kidney failure? Is it the level prior to PTH compensation that they want? D: +
miriamp3  @paperbackwriter what it works for me ;;;; is find the first abnormality so CKD low calcitriol (no D vit) ---> is gonna increase PTH ---> the kidney are not working (chronic, they don't tell u recently- you can;t revert a CKD so the kidney never going to catch up) --> increase inorganic phosphorus.--> always start with the problem. I also use this for celiac and types of shocks. start with the problem, and trust yourself. +4
paperbackwriter  @miriamp3 thank you! I will try out your strategy next time!! :) +1
snripper  I thought renal insufficiency -> inability to reabsorb phosphate at PCT -> decreased phosphate? +3
skonys  Can someone explain why calitriol is low? Is it just that his kidneys are fucked and he can't make it? So PTH is increasing to try to lower the phos and raise the vit d but the kidneys are like "lol, I can't" +
madamestep  @skonys pretty much yup! In early renal failure you'll see high PTH levels but NORMAL Ca and Phos. Becuase it's able to keep up but barely. At a certain point though, the kidney bows out and PTH is high, Phos is high, Ca2+ is low, EPO is low, calcitriol is low, Creatine is high, BUN is high. +



 +0  upvote downvote
submitted by โˆ—cassdawg(1780)
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If the patient is taking calcium acetate (a phosphate binder), why is his phosphorus level increased?

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 -8  upvote downvote
submitted by โˆ—sne(59)
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Since she has celiac spruce --> fat vitamin malabsorption, thus Vit. D is decreased Low vit. D = low calcitriol, low absorption of phosphate from intestine, and low absorption of Ca2+ causing an increase PTH

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