hematology and oncology
Megaloblastic Macrocytic Anemias
Diagnosis of Megaloblastic Macrocytic Anemias
Complete blood count (CBC), RBC indices, reticulocyte count, and peripheral smear B12 and folate levels Megaloblastic anemia is suspected in anemic patients with macrocytic indices. It should also be considered in patients with risk factors who have unexplained paresthesias and/or a high RBC distribution width (RDW). Diagnosis is usually based on Peripheral smear . When fully developed, the anemia is macrocytic, with mean corpuscular volume The RDW is high. Howell-Jolly bodies are common. Reticulocytopenia is present. Hypersegmentation of the granulocytes develops early; neutropenia develops later. Thrombocytopenia is often present in severe cases, and platelets may be bizarre in size and shape. Although iron deficiency can mask macrocytosis, Howell-Jolly bodies and granulocyte hypersegmentation should still be present. Serum B12 and folate levels should be measured. A B12 level < 200 pg/mL (< 147.6 pmol/L), folate level < 2 ng/mL (< 4.53 nmol/L), or RBC folate level < 150 ng/mL (< 340 nmol/L) is generally diagnostic of deficiency. Vitamin B12 levels between 200 and 300 pg/mL (147.6 to 221.3 pmol/L) are nondiagnostic. When vitamin B12 levels are not diagnostic, both a methylmalonic acid (MMA) and homocysteine (HCY) level should be checked. Serum levels of both methylmalonic acid and homocysteine are elevated in vitamin B12 deficiency, while only homocysteine is elevated in folate deficiency. Renal insufficiency elevates the methylmalonic acid level. If vitamin B12 deficiency is confirmed, testing for the presence of autoantibodies to intrinsic factor should be done. Evaluation to determine the cause of the vitamin deficiency should also be done. 