Laboratory investagation of vitamin B12 deficiency

Vitamin B-12 deficiency is not uncommon, particularly in certain patient populations such as elderly, neuropsychiatric, and psychiatric patients. Historically, presentation of vitamin B-12 deficiency was recognized as megaloblastic anemia, which is now rarely seen in Western society. Hematological changes, including macrocytic anemia, are a more well-known symptom, but are not always present or are revealed later in the disease course, However, the advances over the last few decades, from the use of the obsolete Schilling test and total serum vitamin B-12 level to newer methods such as holo-transcobalamin II, the metabolites methylmalonic acid and homocysteine, antibody testing, and gastrin levels, have created a more accurate diagnosis of the disease. Total serum vitamin B-12 level, though sometimes misleading, remains a mainstay of clinical diagnosis. In this work, we will discuss vitamin B-12 deficiency, various diagnostic tests, and an algorithm used in the investigation of vitamin B-12 deficiency.