rubriblast

Ribrublast is a term used in hematology to refer to the earliest identifiable erythroid precursor in the bone marrow, also known as a pronormoblast. It represents the initial stage of red blood cell development during erythropoiesis. In normal marrow, rubriblasts mature through a series of stages, including basophilic normoblast, polychromatophilic normoblast, orthochromatic normoblast, then reticulocyte and finally a mature erythrocyte. The term rubriblast is more common in older or British literature, whereas pronormoblast is the preferred term in many contemporary texts.

Morphology and characteristics: rubriblasts are relatively large cells with a large, round nucleus and finely dispersed chromatin; a prominent nucleolus may be visible. They have a high nucleus-to-cytoplasm ratio and a cytoplasm that stains deeply basophilic because of abundant ribonucleic acid. As maturation proceeds, the cytoplasm becomes lighter and hemoglobin production increases.

Location and development: rubriblasts reside in the bone marrow as the first stage of red cell lineage. Normal erythropoiesis progresses from rubriblast to successive erythroid precursors, culminating in reticulocytes that enter circulation as mature red blood cells.

Clinical significance: rubriblasts are not typically found in peripheral blood. Their appearance outside the marrow, such as in peripheral blood smears, is abnormal and can indicate pathological conditions affecting erythropoiesis, including erythroid leukemia or other myeloid or erythroid dysplasias. In such contexts, their presence prompts further diagnostic evaluation.