Sideroblastic anemia is a form anemia that is characterized by the presence of sideroblasts in the PBFs. Possible etiologies may either be a genetic disorder or indirectly as part of myelodysplastic syndrome, which can exacerbate into hematological malignancies (especially acute myelogenous leukemia).
Patients with sideroblastic anemia do not have iron-deficiency, but the patients' bodies are unable to incorporate iron into the hemoglobin. Hence, RBCs may have granules of iron accumulate in the perinuclear mitochondria and nucleated RBCs may be present
The name Ring sideroblasts is suggestive that the iron granules are arranged in a ring form in the mitochondria around the nucleus. However this do not necessarily mean that a complete ring must be seen for a cell to be identified as a ring sideroblast.
According to WHO 2008 classification, three classification types of sideroblasts:
- Type 1 Sideroblasts: Fewer than 5 siderotic granules in the cytoplasm
- Type 2 Sideroblasts: 5 or more siderotic granules, but not in a perinuclear distribution
- Type 3 or Ring Sideroblasts: 5 or more granules in a perinuclear position, surrounding the nucleus or surrounding at least one third of the nuclear circumference.
Clinical Observations of PBFs
- Dimorphic picture (presence of both normocytic and microcytic RBCs)
- Hence MCV is commonly decreased but maybe normal
- RDW is increased as there is marked poikilocytosis
- Marked anisocytosis
- 20 - 30% hematocrit
- Normal appearance and counts of both leukocytes and platelets
- Serum Iron: High
- Increased ferritin Levels
- Normal total iron-binding capacity (TIBC)
- High transferrin saturation
- Prussian Blue will reveal RBCs that contains blue-green granules (iron) in the cytoplasm. Prussian blue staining involves a non-enzymatic reaction of ferrous iron with ferrocyanide forming ferric-ferrocyanide, which is blue in color. A counter-stain may be used to provide better visualization.