What does megaloblast mean?
A megaloblast is an abnormally large, immature red blood cell precursor formed in the bone marrow. Megaloblasts are especially associated with megaloblastic anemia, a group of disorders commonly linked to deficiencies of vitamin B12 or folate, although other causes are possible. Their development reflects impaired DNA synthesis, which prevents the cells from dividing and maturing normally; as a result, large megaloblasts may accumulate in the marrow and abnormally formed red cells may appear in the blood. The term is chiefly used in medical and hematological contexts. In those settings, it distinguishes an abnormal red-cell precursor from an ordinary erythroblast, which is the more general term for an immature red blood cell. “Megaloblastic” is the corresponding adjective, as in “megaloblastic anemia” or “megaloblastic changes.”
nounA large, immature red blood cell precursor that develops abnormally in the bone marrow, especially in megaloblastic anemia.
- An abnormally large immature red blood cell precursor, typically found in the bone marrow in megaloblastic anemia.
- Historically, a large erythroblast or other nucleated red-cell precursor, especially one undergoing abnormal maturation.
"The blood test revealed megaloblasts, indicating impaired DNA synthesis."
"Marrow examination showed numerous megaloblasts and pronounced megaloblastic changes."
"Vitamin B12 deficiency can cause megaloblasts to accumulate because impaired DNA synthesis prevents normal red-cell maturation."
The plural is used when referring to multiple megaloblasts or to the cells as a class.
"Megaloblasts were visible in the bone-marrow sample."
A megaloblast is literally an oversized blast: its name combines the Greek roots for “large” and “germ” or “sprout,” reflecting its abnormal size.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of megaloblast
The word combines the Greek roots megalos, meaning “large,” and blastos, meaning “germ,” “sprout,” or an immature cell. It was coined in the nineteenth century to describe large nucleated red-cell precursors observed in disorders of blood-cell formation. Related English terms, including blastocyst and blastula, share the second root but refer to different biological structures.
Related word forms
How megaloblast is actually used
This is primarily a medical and hematological term. It is usually used in specialist descriptions of marrow or blood-cell disorders and is less appropriate in general speech than “megaloblastic anemia.”
Easily confused with megaloblast
An erythroblast is any immature red blood cell precursor, whereas a megaloblast is an abnormally enlarged erythroblast associated with defective DNA synthesis.
A megaloblast develops from red blood cell precursors, while a megakaryocyte is a large bone-marrow cell that produces platelets.