The iron content assessment of a bone marrow film stained with Prussian blue is semi-quantitative, i.e., a mean estimate at 100 and 400-fold magnification.
A 4-step classification is used:
- no storage iron
- decreased storage iron
- normal storage iron
- increased storage iron
In the iron stain with Prussian blue, iron stains blue to blue-green and the cell constituents are red. Iron ist stored in two forms in the bone marrow: The major part is storage iron and is mainly present in macrophages. This is hemosiderin. The second form is iron as small granules in erythropoietic cells (sideroblasts / ringed sideroblasts).The iron content in the bone marrow is a good indicator of the body's iron stores. As a measurment for iron storage in the body, it is obsolete. Themeasurement of serum ferritin is more precise, easier to obtai and less invasive.
In the normal iron state, coarse blue granules are found equally distributed throughout the bone marrow film. With an decreased iron storage they are more rarely seen and with no storage iron they are absent. The hemosiderin granules are densely packed with an increased iron storage.
Sideroblasts and ringed sideroblasts:
While single sideroblasts (left image) are normal in the bone marrow, ringed sideroblasts (right image) indicate a sideroblastic defect (abnormal iron metabolism). By definition, the ringed sideroblasts contain 5 or more garnulas that cover upat least on third of the nucleus' circumference.