Schilling Test

You have a patient who has Macrocytic Anemia and you have done neuro exam and have determined there are neuro problems so now you know that your patient has a Vitamin B12 deficiency not a folate deficiency. 

How do you determine what is causing the Vitamin B-12 deficiency?

The answer is the Schilling test but let's break it down further. The point of the Schilling test is to determine if the B-12 deficiency is from Lack of dietary intake or Pernicious Anemia, or Malabsorption

Step 1 = Inject the patient with pure B-12 and this will saturate all the B-12 storage places (liver). now have the patient drink radio labeled B-12 and when the radio-labeled B-12 gets to the liver and tries to get stored it is turned away as there is no room left because of the pure B-12 previously injected. When it is turned away it goes to the kidney and gets pissed out. 

 

Normal = 5%: 

If the patient's urine has 5% radio-labeled B-12 in it then it is normal and you have ruled out malabsorption issues including pernicious anemia (lack of intrinsic factor). Patient is Normal. So the B-12 deficiency could be to plain lack of dietary intake. Tx = vitamin b- 12 supplements.

Deficient = less than 5%:

If the patients urine contains less than 5% radio-labeled B-12 then you know that the patients B-12 deficiency is caused by pernicious anemia (loss of Intrinsic factor) or other malabsorption problems

Step 2: Now to distinguish between pernicious anemia and other malabsorption pathology:

Inject pure B-12 with Intrinsic Factor. Then have the patient drink radio labeled B-12. 

If the patient's urine contains 5% radio-labeled B-12 you will know that the Vitamin B-12 deficiency is due to lack of Intrinsic Factor (Pernicious Anemia). 

If the patient's urine has less 5% radio-labeled B-12 then you have ruled out pernicious anemia, which means that the B-12 deficiency is due to other malabsorption issues which has numerous causes. 

Step 3: To rule out Chronic Pancreatitis as a cause of malabsorption leading to B-12 deficiency, You can give the patient pancreatic enzymes and the follow it with radio-labeled B-12. If the 24 hour urine has 5% B-12 the you have Diagnosed B-12 deficiency due to chronic pancreatitis. Pancreatitis causes B-12 deficiency because there are pancreatic enzymes necessary to cleave the R-factor off of the B-12 - R-factor complex. If these enzymes are absent then the body can't absorb the B-12. If there is less than 5% B-12 in the urine then you have ruled out Chronic Pancreatitis. 

Step 4: Now you can rule out Bacterial overgrowth by giving the patient a 10 day coarse of broad spectrum antibiotics followed by radio-labeled B-12. Then if the patient's 24 hour urine has 5% (normal) B-12 in it then you have diagnoses Vit B-12 deficiency due to Bacterial Overgrowth. If there is less than 5% B-12 in the urine then you have ruled out bacterial overgrowth.

If you make it to this point with the patient and you still do not have you diagnosis you must assume the B-12 deficiency is due to something other than what you ruled out. There are many other causes but the Schilling Test rules out or rules in the more common causes. Some other causes could be:

Crohn's disease, Diphyllobothrium latum (fish tape worm), and others.