Megaloblastic bone marrow Abnormal increased number of megaloblasts in the bone marrow. HP:0001980 SNOMEDCT_US:167921008 UMLS:C0238801 A megaloblast is an abnormally large nucleated red blood cell found especially in people with pernicious anemia. Megaloblasts, like their normal counterparts, normoblasts, are immature red cell precursors in the bone marrow. Megaloblasts display both a larger size than normoblasts as well as a fine reticular nuclear structure. Abnormality of multiple cell lineages in the bone marrow