Schillings on USMLE/COMLEX

[docmo83]

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I am new on this site and this is my first thread!😀 So I hope it comes in handy!

My question has to do with the Schillings test on the usmle/comlex exam. I did some questions on UW pertaining to this test and their explanations threw me off. So...can anybody explain it to me perhaps in a clearer fashion? If anybody has taken the exam already, can they remember how they asked it?

Thanks much!

 

[FutureInternist]

For some reason I cannot attach stuff so here goes.

Give pt IM B12 to saturate the tissues, then p.o. radiolabelled B12 to see how much ends up in the body. Collect urine after 24 hrs & see how much radio-B12 is in there. Normal is 10% while <5% is abnormal

After the first try if you get a normal response (i.e. 10% or more) then there is nothing wrong w/ absorption & so patient is either not eating enough B12 or losing too many RBCs

If you get an abnl response then absorption is a problem.....so either pt has no IF (needed for B12 absorption), bad villi, or mechanical obstruction

So step 2 of test is to add IF & repeat test. If you get normal response now, pt has pernicious anemia (i.e. IF deficiency - which you fixed), if response still abnormal then you give antibiotics & repeat test a third time. If response now normalises then pt had bacterial overgrowth, impeding absorption (which got killed by Abx). If however you still get an abnormal response then the patient has one of the other malabsoprtion syndromes (Crohn's, Whipple's, short ileum etc)

Hope that helps. I have a sweet algorithm on excel but can't attach for some reason.
Can email to you if you PM me your email address

 

[ACE Stimulator]

For some reason I cannot attach stuff so here goes.

Give pt IM B12 to saturate the tissues, then p.o. radiolabelled B12 to see how much ends up in the body. Collect urine after 24 hrs & see how much radio-B12 is in there. Normal is 10% while <5% is abnormal

After the first try if you get a normal response (i.e. 10% or more) then there is nothing wrong w/ absorption & so patient is either not eating enough B12 or losing too many RBCs

If you get an abnl response then absorption is a problem.....so either pt has no IF (needed for B12 absorption), bad villi, or so mechanical obstruction

So step 2 of test is to add IF & repeat test. If you get normal response now, pt has pernicious anemia (i.e. IF deficiency - which you fixed), if response still abnormal then you give antibiotics & repeat test a third time. If response now normalises then pt had bacterial overgrowth, impeding absorption (which got killed by Abx). If however you still get an abnormal response then the patient has one of the other malabsoprtion syndromes (Crohn's, Whipple's, short ileum etc)

Hope that helps. I have a sweet algorithm on excel but can't attach for some reason.
Can email to you if you PM me your email address

i have problem with this as well...thanks for the explanation.

 

[FutureInternist]

Ok.....so the "me not being able to attach stuff" is not an SDN problem, but my computer....Will try to fix it & post here......but don't hold your breath 🙂

 

[Booner]

Thanks for the stepwise explanation, I had only read about step 2 in your response, nice to have the additional steps for further clarification of the possible issues.

 

[FutureInternist]

Q via PM

See, what throws me off is why does a high excretion mean normal absorption? If it is absorbed, shouldn't it not be in the urine? And vice versa, if B12 is low in the urine, shouldn't that mean the patient absorbed it? That is what confuses me.

Well since you're giving them p.o. radio- B12 the only way for it to show up in the urine is to get absorbed into the blood & then go into the urine. The reason it doesn't stay in the body is that you already saturated the body w/ normal B12 so when your body absorbs the radio-B12, there is an excess & that extra radio-B12 is out the urine

 

[ACE Stimulator]

Ok.....so the "me not being able to attach stuff" is not an SDN problem, but my computer....Will try to fix it & post here......but don't hold your breath 🙂

have you tried screencapture and attach it as an image?

 

[FutureInternist]

Fixed the computer 😀
Hope this helps

 

[equilibr8]

Sorry to bring back an old thread, but I had question about Schillings test.

"Give pt IM B12 to saturate the tissues, then p.o. radiolabelled B12 to see how much ends up in the body. Collect urine after 24 hrs & see how much radio-B12 is in there. Normal is 10% while <5% is abnormal."

If the patient has < 5% radioactive B12 in urine, the rest of the radioactive B12 is in stool? So my question for you is, why don't you collect a stool sample? Is urine test easier?