Why hyperuricemia in Crohn's disease? - USMLE Forums
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Old 03-01-2011
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Question Why hyperuricemia in Crohn's disease?

Can someone explain this, please?
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Old 03-01-2011
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From what I have read, it looks like the hyperuricemia is secondary to diarrhea. Diarrhea can lead to a metabolic alkalosis and thus more acidic urine. Uric acid formation is favored with low urine pH (this is why treatment for uric acid stones includes alkalanizing urine).

Hydrogen ions + Urate (soluble) = Uric acid (insoluble) --> This is favored by low pH
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Old 03-01-2011
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Quote:
Originally Posted by apx85 View Post
From what I have read, it looks like the hyperuricemia is secondary to diarrhea. Diarrhea can lead to a metabolic alkalosis and thus more acidic urine. Uric acid formation is favored with low urine pH (this is why treatment for uric acid stones includes alkalanizing urine).

Hydrogen ions + Urate (soluble) = Uric acid (insoluble) --> This is favored by low pH
Doesn't Diahrrea lead to a metabolic acidosis? (Increased excretion of HCO3) That will lead to a decreased pH!
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Old 03-01-2011
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@patelMD

Increased loss of HCO3- is indeed the mechanism of Metabolic acidosis in diarrhea, but it is lost through the GI tract, not the urine. The kidney will try to compensate for the loss of HCO3- in diarrhea by increasing the reabsororption of HCO3- and increasing renal losses of H+

Thus, the the urine will become more acidic.
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Old 03-01-2011
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Quote:
Originally Posted by apx85 View Post
@patelMD

Increased loss of HCO3- is indeed the mechanism of Metabolic acidosis in diarrhea, but it is lost through the GI tract, not the urine. The kidney will try to compensate for the loss of HCO3- in diarrhea by increasing the reabsororption of HCO3- and increasing renal losses of H+

Thus, the the urine will become more acidic.

Yes, that makes complete sense. Thanks!
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Old 03-01-2011
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Quote:
Originally Posted by apx85 View Post
From what I have read, it looks like the hyperuricemia is secondary to diarrhea. Diarrhea can lead to a metabolic alkalosis and thus more acidic urine. Uric acid formation is favored with low urine pH (this is why treatment for uric acid stones includes alkalanizing urine).

Hydrogen ions + Urate (soluble) = Uric acid (insoluble) --> This is favored by low pH
Thanks a lot.
I just wondering could uric acid stones be also caused by increased cell turnover or by some medications used in treatment of Crohn?
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Old 03-02-2011
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@Pav100

I'm not sure. The explanation I read on UptoDate mentioned the diarrhea but not anything about cell turnover
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Old 03-02-2011
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[QUOTE=apx85;30237]@Pav100



(just to nail this concept), is this correct that any chronic diarrhea can potentially lead to uric stone formation?
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Old 03-02-2011
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I found this online:

Hyperuricosuria develops in chronic diarrhea, high purine intake, and is associated with tumor lysis after chemotherapy or radiation. Oddly enough, calcium stones may develop in patients who excrete too much uric acid (hyperuricosuria). When urine is less than pH 5.5, uric acid crystals develop and calcium crystals then begin layering around this crystal to form a calcium oxalate stone.

So chronic diarrhea can lead to increased uric acid in the urine with increased risk of both uric acid and calcium oxalate stones.

NOTE: This is might be more for Step 2 (I came across it in the step 2 forum) but patients with Crohn's disease have very high risk for calcium oxalate stones. Calcium binds to the malabsorbed fat, leaving oxalate available for absorption. This increases oxalate in the blood, which then concentrates in the urine and forms calcium oxalate stones.
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Old 06-17-2011
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Correct Answer tnx

thanks. I think your answer is true. my answer is similar to yours.
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Old 06-17-2011
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@apx85
I didnt understand the explanation of hyperuricemia in diarrhea. Plz elaborate.i read that diahrrhea causes hyperchloremic acidosis due to loss of HCO3. i get that acidosis cause more HCO3 reabsorption and more acidic urine ,but non anion gap acidosis doesnt cause hyperuricemia. ?
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Old 06-17-2011
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Quote:
Originally Posted by sandy_presto3 View Post
@apx85
I didnt understand the explanation of hyperuricemia in diarrhea. Plz elaborate.i read that diahrrhea causes hyperchloremic acidosis due to loss of HCO3. i get that acidosis cause more HCO3 reabsorption and more acidic urine ,but non anion gap acidosis doesnt cause hyperuricemia. ?
Unfortunately I can't really elaborate any further. This is not a very high yield concept at all for Step 1 so I wouldnt worry about it. There are so many ways to get hyperuricemia that I highly doubt the mechanism will be tested unless it is the classic increased cell turnover, chemotherapy, or some metabolic disease.
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