Key Points. 1  Megaloblasts are large nucleated RBC precursors with noncondensed chromatin. 2  The most common causes of megaloblastic, macrocytic anemia are deficiency or defective utilization of vitamin B12 or folate. 3  Do CBC, RBC indices, reticulocyte count, and peripheral smear.
Wiktionary (0.00 / 0 votes) Rate this definition: vein (Noun). A blood vessel that transports blood from the capillaries back to the heart. vein (Noun). (used in plural veins) The entrails of a shrimp. vein (Noun). In leaves, a thickened portion of the leaf containing the vascular bundle. vein (Noun).
Definition of vein for English Language Learners. : 1  any one of the tubes that carry blood from parts of the body back to the heart. : 2  any one of the thin lines that can be seen on the surface of a leaf or on the wing of an insect. : 3  a long, narrow opening in rock filled with gold, silver, etc.