Schilling Test - MADE SIMPLE

Schilling test: Is a Medical investigation tool used for patients with B12 Deficiency to determine the underlying cause.

1. Stage 1: Give ORAL vitamin B12 “Radiolabeled B12” + Intramuscular Vitamin B12 “Unlabeled B12” and we wait 24 Hours and measure patients Urine for "Radiolababeled Vitamin B12"

The reason for Intramuscular injection of B12 is to saturate all B12 receptors in the liver with NORMAL B12 (unlabeled b12) so we PREVENT binding of oral vitamin B12 “Radiolabeled B12”. Therefore if Radiolabeled vitamin B12 is absorbed from the GI tract, it will get excreted into the urine. After 24 hours the patients urine is collected for assessment.

• A NORMAL result shows High Radiolabeled Vitamin B12 in the urine over the first 24 hours and this gives your gives your diagnosis as "Dietary Deficiency of B12".
• If there is Low levels of Radiolabeled in the urine, then we go to the next stage (stage 2).

NOTE: We will give Intramuscular B12 only ONCE in the beginning since it takes years for B12 to be depleted from the body, therefore B12 receptors are going to be fully saturated after the first injection and there is no need for more B12 injection for the remaining steps of this test.

2. Stage 2--> Vitamin B12 + Intrinsic Factor

The reason we give Intrinsic Factor to our patient is to investigate to see if our patient has Intrinsic Factor deficiency. 

• If the patient's urine collection comes out normal (high Radiolabeled B12), we will then conclude that there is Intrinsic factor Deficiency (e.g. Pernicious Anemia which is an Autoimmune Gastritis)
• If the urine still has LOW radiolabeled B12, we will move onto stage 3.

3. Stage 3 --> Vitamin B12 + Antibiotics.

• If now the Urine collection is Normal (High Radiolabeled B12) then we conclude that patients B12 deficiency was due to Bacterial Overgrowth Syndrome which causes malabsorption. The Terminal ilium is very narrow due to the fact that it contains many lymphoid tissues known as (Peyer’s patches) which are responsible for secretion of IgA antibodies which defend the G.I. against bacterial invasion.
• If the urine still has LOW radiolabeled B12, we will move onto stage 3.

4.Stage4 --> Vitamin B12 + Pancreatic Enzymes (protease)

• If the Urine Collection is now NORMAL (HIGH Radiolabeled B12) then we conclude that the patient B12 Deficiency was due to Pancreatic Insufficiency (e.g. Chronic Pancreatitis). Because Pancreas contains many enzymes that aid digestion. One of these enzymes is called "protease" which is responsible for breaking off this group of protein called "R-proteins that is bound to Vitamin B12. The job of protease is to get rid of the "R-protein" so B12 can become a free and  bind to Intrinsic Factor which will help vitamin B12 absorption in the terminal ilium. Without protease, B12 will remind connected to R-protein and therefor will not be able to bind Intrinsic factor, and it will not get absorbed through the terminal ilium resulting in its malabsorption.

Vitamin B12 Deficiency Symptoms:

• Megaloblastic anemia ( look for Hypersegmented neutrophils)
• Neurological manifestations (e.g. Paresthesia, which is burning and tingling sensation in the extremities) 
• Homocystinuria which causes kyphosis, lens subluxation and atherosclerosis.