Intrinsic factor (IF), or anti-intrinsic factor, intrinsic factor " “blocking antibody, type 1 intrinsic factor antibody, IFAB, is a glycoprotein produced by the gastric parietal cells. It binds to, transports, and facilitates absorption from the terminal ileum of the very small amount of vitamin B12 in the diet. If there are antibodies to the parietal cells, the B12-binding site of IF, or the binding site of IF to the ileum, the patients ability to absorb dietary B12 by the IF route will be reduced. Over time, the presence of these antibodies leads to a reduction in B12 stores and ultimately to vitamin B12 deficiency, the consequences of which vary. The presence of circulating autoantibodies to IF is a very specific indicator of PA. Antibodies against IF are found in approximately 50% of cases but rarely in other conditions.
Normal range: negative.
Use
Diagnosis of PA
Evaluation of patients with decreased vitamin B12 levels
Interpretation
Increased in PA
Limitations
Cyanocobalamin may give a false-positive test result.
Methotrexate and folic acid may give false-positive test results.
Negative or inconclusive test results do not exclude the diagnosis of PA.
Some patients with other autoimmune diseases may have positive test results, particularly in patients with autoimmune thyroid disease or type 1 DM.