Bone marrow specimens from a large group of infants and children were studied with the prussian blue stain. Iron-staining granules were present in the normoblasts of all the subjects studied, including normal individuals and those with a large variety of hematologic disorders. The term sideroblast was proposed for normoblasts with nonstaining inclusions. The profound decrease in sideroblasts in iron deficiency anemia and their prompt increase following both iron therapy in vivo and the addition of iron to marrow cultures in vitro indicated that the estimation of normoblast iron granules provides a sensitive index of the availability of iron. In thalassemia and in lead poisoning, hemoglobindeficient erythrocytes were found despite the presence of abundant iron granules within the normoblasts.

The presens of stainable nonhemoglobin iron in red cell precursors is a normal phenomenon and provides a useful adjunct for the study of iron metabolism.

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