Schilling Test

[SBK]

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Can anyone explain this to me?

I understand that you give the person radio-labelled B12 + IM injection to ensure that there is circulating B12.

Low excretion during this phase means that your body took up some of the labelled B12...meaning the patient had a poor diet

So now you know there is absorption issues (P. anemia or intestine problem)

So know you give B12 + IF.

UWOLRD now says "if the cause of impaired absorption is lack of IF, urinary excretion would increase"

How does this make sense? If IF was the problem, wouldnt your body immediately absorb it since it is there complexed to B12, implying a lower excretion rate?

 

[RySerr21]

Can anyone explain this to me?

I understand that you give the person radio-labelled B12 + IM injection to ensure that there is circulating B12.

Low excretion during this phase means that your body took up some of the labelled B12...meaning the patient had a poor diet

So now you know there is absorption issues (P. anemia or intestine problem)

So know you give B12 + IF.

UWOLRD now says "if the cause of impaired absorption is lack of IF, urinary excretion would increase"

How does this make sense? If IF was the problem, wouldnt your body immediately absorb it since it is there complexed to B12, implying a lower excretion rate?

You are confused about why you give the injection. You are trying to saturate the bodies stores of B12. Therefore, ANY OTHER SOURCE OF B12 THAT IS ABSORBED WILL BE PEED OUT. So, if you check their urine and there is no B12, you know it was never absorbed from the intestine, b/c if it was it would have been peed out and not used by teh body.


First phase: radiolabled B12 + injection of non radiolabeled

The injection is to saturate the bodies stores of B12 so that if the radiolabled B12 is absorbed, it will be peed out and detected in the urine.

If you detect radiolabeled B12 in this stage, then the person was just deficient in B12 (you did nothing but give them B12). If you do not detect radiolabeled B12, then there is soething wrong with the absorption process...proceed to phase two.


Phase two: injection of nonradiolabeled and given oral radiolabeled B12 WITH INTRINSIC FACTOR. At this stage, if you detect B12 in the urine, you can say that the patient was deficient in intrinsic factor (b/c you just gave them it and it worked). If still nothing happens, then you the problem is not with a lack of B12 or a lack of IF. The problem must be down stream, either a worm or maybe the pt has absorption problems in the terminal ileum.

 

[spicedmanna]

Can anyone explain this to me?

I understand that you give the person radio-labelled B12 + IM injection to ensure that there is circulating B12.

Low excretion during this phase means that your body took up some of the labelled B12...meaning the patient had a poor diet

So now you know there is absorption issues (P. anemia or intestine problem)

So know you give B12 + IF.

UWOLRD now says "if the cause of impaired absorption is lack of IF, urinary excretion would increase"

How does this make sense? If IF was the problem, wouldnt your body immediately absorb it since it is there complexed to B12, implying a lower excretion rate?

The Schilling test is outdated, but I guess still tested on the boards. I haven't seen anybody use it, except when they aren't sure and need something to confirm suspicions.

There are several stages to the test:

Stage I: Unlabeled-B12 given IM + Radiolabeled-B12 given PO. Here you are testing how much radiolabeled-B12 gets absorbed through the GI tract. You give enough Unlabeled-B12 to saturate the receptors in the liver and other body tissues. Therefore, the Radiolabeled-B12 that gets absorbed through the GI tract will be excreted in the urine. A 24hr urine is sampled to see how much of it passes through. If it's greater than or equal to 5%, then your gut is absorbing B12 adequately.

Stage II: If the patient fails Stage I (i.e., excretes less than 5% in a 24hr period), then you move onto Stage II. Here, you repeat Stage I, but also add Intrinsic Factor (IF) PO. You collect a 24hr urine. If this normalizes the abnormality seen in Stage I, you know that the patient lacks IF and has Pernicious Anemia. If, however, the abnormality still exists, then you know low or absent IF is not the cause, but some other kind of malabsorption issue, like worms (the infamous Diphyllobothrium latum), hepatobiliary or pancreatic problems, Celiac or Whipple's Disease, bacterial overgrowth syndrome, etc.

Stage III: If the patient fails Stage II, and you suspect bacterial overgrowth, you repeat the test and also give ABX, to see if that is the problem.

Stage IV: If the patient fails Stage II, and you suspect pancreatic problems, you repeat the test and also give pancreatic enzymes.

Reference: http://en.wikipedia.org/wiki/Schilling_test