Pernicious Anemia - Diagnosis

Diagnosis

The insidious nature of the disease may mean a diagnosis is delayed. PA is suspected when the patient's blood smear shows large, fragile, immature erythrocytes (megaloblasts).

IF antibodies are highly suggestive for a diagnosis of PA, and are found in nearly 100% of patients, with a sensitivity of around 70%. Antiparietal cell antibodies are inferior to intrinsic factor antibodies, as they are less sensitive and less specific. Elevated gastrin levels and decreased pepsinogen I levels may also be found, although these findings are less specific to pernicious anemia.

The Schilling test is the classic test for PA, but it is no longer widely used, as there are other quicker and easier methods (in addition to difficulties with the radiolabelled agent). The other main diagnostic signpost of low levels of serum B₁₂ cannot be relied upon, as sufferers can have high levels of serum B₁₂ and still have pernicious anemia. Blood and urine tests for methylmalonic acid may indicate a B₁₂ deficiency, even though serum B₁₂ is within the normally acceptable range. Serum B₁₂ is not necessarily an indicator of efficient use by the body, in the muscles, for example.

A diagnosis of PA first requires demonstration of megaloblastic anemia (through a full blood count), which evaluates the mean corpuscular volume (MCV), as well the mean corpuscular hemoglobin concentration (MCHC). Pernicious anemia is identified with a high MCV and a normal MCHC (that is, it is a macrocytic, normochromic anemia). Ovalocytes are also typically seen on the blood smear, and a pathognomonic feature of megaloblastic anemias (which include PA and others) is hypersegmented neutrophils.

Pernicious anemia can also be diagnosed by evaluating its direct cause, vitamin B₁₂ deficiency, by measuring B₁₂ levels in serum. A Schilling test can then be used to distinguish pernicious anemia from other causes of B₁₂ deficiency (notably malabsorption).

The diagnosis of atrophic gastritis type A should be confirmed by gastroscopy and stepwise biopsy. Approximately 90% of individuals with PA have antibodies for parietal cells; however, only 50% of all individuals in the general population with these antibodies have pernicious anemia.