D XYLOSE TEST

[shigella123]

I'm not really clear about this concept so please correct me if I'm wrong.

D-xylose absorption needs intact mucosa for absorption so if the mucosa is damaged by bacterial or inflammation then it won't be absorbed and so you will have normal levels in urine and blood?

In case of terminal ileum disease such as crohns, since we have damaged mucosa then D-xylose will be normal to decreased in urine and blood since we have skipped lesions and some will be absorbed? Gosh I'm so confused...

Let me try again... in terminal ileum dz we have decreased bile salts so no fat absorption, also bacteria de-conjugates bile salts so further decrease in fat absorption. Increase bacteria will use up the monosaccharide D-xylose and so there will be decreased excretion in Urin and blood? After treatment with antibiotics there will be normal D-x in urine and blood?

I also read if there is no increase in D-x after antibiotic Rx then there's no bacteria involved and so if the intestinal mucosa is damaged then its by whipples, celiac, tropical sprue, gardeneralla, hookworm, etc?
And there is increased in D-x value in Hodgkins and scleroderma?

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[Apoplexy__]

Hahaha hopefully this breakdown will clear things up:
-D-xylose is a monosaccharide, so all you need to absorb it is intact intestinal villi.
-D-xylose showing up in the urine is a normal sign, because that means it was intestinally absorbed. It's not metabolized, so it just ends up in the urine filtrate. D-xylose in urine = negative test.
-A positive test (no absorption, decreased urine output) means that there's something wrong with absorption at the mucosa: Crohn's, villous blunting (post-gastroenteritis or sprue), etc.
-A negative test means that it could be anything else that causes malabsorption with nothing to do with the villi (pancreas, gallbladder, enzyme deficiency, etc.)
-The only confounder of this test is the antibiotics twist: Bacteria can uptake D-xylose and cause false positives. If you suspect bacterial overgrowth, you can give antibiotics, which should turn the test from positive to negative if it was because of bacteria. If it wasn't, the test will stay positive (urine output of D-xylose will stay decreased)
-Not sure about those weird ones like Hodgkin's and scleroderma...but if the mechanism that was proposed by whatever source you learned those from included mucosal damage/villous blunting, then the D-xylose test would be positive.

 

[Fatalis]

IMPORTANT: if you give an ab and the results are still the same, you CAN NOT rule out whipple disease, the infection takes months to cure! So in short, if you suspect bacterial overgrowth, and the test improves with an ab it was bacterial overgrowth; if the results do not improve with an ab use, it can still be whipples disease

 

[Modeselektor]

Pretty much @kirbymiester covered it.

Another cool thing to know is that another way to differentiate malabsorption occuring from non-pancreatic causes (eg: celiac) vs. chronic pancreatitis look at the blood:

You need pancreatic enzymes to absorb B12,
You only need an intact bowel wall to absorb iron.

If a patient has iron deficiency anemia, it's not chronic pancreatitis, it's celiac or something along those lines.

 

[shigella123]

Thank you everyone!

I'll be back soon with more questions for you guys.. lol...

 

[shigella123]

Got it.. just read the experience threat...won't ask step 2 question just yet... Thanks again everyone!