The body needs vitamin B₁₂ to produce red blood cells and to maintain a healthy nervous system. Too little vitamin B₁₂ can result in low levels of hemoglobin, the substance in red blood cells that carries oxygen. Low levels of vitamin B₁₂ can also cause problems with the nervous system, including memory loss, dementia, and damage to the nerves supplying the hands and feet (peripheral neuropathy).

A vitamin B₁₂ deficiency can be caused by a lack of the vitamin in the diet or, more commonly, by a problem with absorbing the vitamin from the intestines. A substance called intrinsic factor helps the intestines absorb vitamin B₁₂. The inability to absorb vitamin B₁₂ properly may be due to a lack of intrinsic factor or to a problem with the intestines.

The Schilling test evaluates the body's ability to absorb vitamin B₁₂ (see Vitamin B₁₂ test). It measures the amount of vitamin B₁₂ passed in urine after a person swallows a known amount of vitamin that is tagged with a radioactive substance. If the intestines are able to absorb vitamin B₁₂ normally, a certain percentage of the vitamin (up to 25% of the amount swallowed) will be passed in the urine. If the intestines cannot absorb the vitamin normally, very little or no vitamin B₁₂ will be present in the urine.

A Schilling test with abnormal results (no vitamin B₁₂ in the urine) may be repeated after giving the person intrinsic factor by mouth. This repeat test can tell whether the vitamin deficiency is due to a lack of intrinsic factor or due to a problem with the intestines.

The amount of radioactive vitamin B₁₂ is usually measured in a sample of all the urine the person produces over 24 hours (24-hour urine sample).

Schilling Test
Results

Normal

Normal values may vary from lab to lab.

If the Schilling test is normal but blood levels of vitamin B₁₂ are low, it may mean that you are not getting enough vitamin B₁₂ in your diet. It may also mean that blood levels of vitamin B₁₂ may have appeared low when they were actually normal.

Lower than normal values may mean

• First test abnormal (less than 7% of the radioactive vitamin B12 found in the urine). This means a second test with the addition of intrinsic factor is needed to find the cause of the problem.
• Second test normal (adding intrinsic factor results in normal levels of radioactive vitamin B12 in the urine). This means that you have pernicious anemia and are not producing the intrinsic factor you need to absorb vitamin B₁₂ from your intestines.
• Second test abnormal (adding intrinsic factor does not produce normal levels of radioactive vitamin B12 in the urine). This result means a problem other than a lack of intrinsic factor. Causes of a second abnormal Schilling test include an intestinal disease (such as sprue or celiac disease), liver disease, or an underactive thyroid gland (hypothyroidism).
• Third test normal (after receiving antibiotics or pancreatic enzymes). A third test may be done after you receive antibiotics to kill bacteria in the intestine. If the third test is normal (adding intrinsic factor results in normal levels of radioactive vitamin B₁₂ in the urine), it may mean you have an overgrowth of bacteria in your intestine. A third test may also be done after you receive a course of pancreatic enzymes if your doctor suspects your pancreas is not working properly. If the third test is normal, it may mean that your pancreas is not working properly.