Development and Validation of an Automated Chemiluminometric Immunoassay for Human Intrinsic Factor Antibodies in Serum

Abstract

The cobalamins, also referred to as vitamin B12, are a group of closely related enzymatic cofactors involved in the conversion of methylmalonyl-coenzyme A to succinyl-coenzyme A and in the synthesis of methionine from homocysteine (1)(2)(3). Vitamin B12 deficiency can lead to megaloblastic anemia and neurologic deficits (4). The latter may exist without anemia or precede it. Adequate replacement therapy will generally improve or cure cobalamin deficiency. Unfortunately, many other conditions, which require different interventions, can mimic the symptoms and signs of vitamin B12 deficiency (4). Moreover, even when cobalamin deficiency has been established, clinical improvement may require different dosages or routes of vitamin B12 replacement, depending on the underlying cause (3)(4). In particular, patients with pernicious anemia, possibly the commonest type of cobalamin deficiency in developed countries, require either massive doses of oral vitamin B12 or parenteral replacement therapy (3)(4)(5). The reason is that in pernicious anemia, patients suffer from gastric mucosal atrophy, which leads to diminished or absent gastric acid, pepsin, and intrinsic factor (IF) production. Because gastric acid, pepsin, and IF are required for liberation of cobalamin from binding proteins and efficient cobalamin absorption in the gut, respectively, vitamin B12 deficiency ensues (3)(4). Most of these patients have autoantibodies against gastric parietal cells or IF, with the latter being very specific but present in only ∼50% of cases (1). The aim of the work-up of patients with suspected vitamin B12 deficiency is therefore to confirm the presence of deficiency and to establish its most likely etiology. Many different testing algorithms have been proposed to achieve maximum sensitivity and specificity for both tasks, but almost all involve measurement of serum vitamin B12 and IF antibodies (IFABs) at …