nonmegaloblastic

Nonmegaloblastic describes a set of conditions in which macrocytosis or anemia occurs without the megaloblastic changes seen in impaired DNA synthesis, such as the presence of megaloblasts in the bone marrow. In megaloblastic anemia, deficiency of vitamin B12 or folate disrupts nuclear maturation, producing large, immature red blood cell precursors. By contrast, nonmegaloblastic states produce macrocytosis or anemia through other mechanisms, and hypersegmented neutrophils or megaloblasts are typically absent.

Common causes include liver disease and chronic alcohol use, both of which can enlarge red blood cells without triggering megaloblastic bone marrow changes. Hypothyroidism, reticulocytosis from acute blood loss or hemolysis, and certain medications or toxins can also lead to macrocytosis without megaloblastic features. Some drugs (and scenarios with increased reticulocyte production) raise the red cell size independently of DNA synthesis defects.

Diagnosis relies on a combination of laboratory and clinical findings. Complete blood count often shows an elevated mean corpuscular volume (MCV). Peripheral blood smear may reveal macrocytosis or macrocytes but lacks the hypersegmented neutrophils and other megaloblastic features. Serum levels of B12 and folate are typically normal, though values may be equivocal in mixed conditions. Assessment of liver function, thyroid function, alcohol use, drug history, and reticulocyte count helps identify the underlying cause. Bone marrow examination is usually not required unless diagnosis remains uncertain.

Management focuses on addressing the underlying cause (e.g., treating liver disease, reducing alcohol intake, correcting thyroid dysfunction, or adjusting medications).