What are marrow normoblasts containing bright-blue iron specks when stained called and what special stain is commonly used?

Sideroblasts and Prussian Blue Stain

Marrow normoblasts containing bright-blue iron specks when stained are called sideroblasts and are commonly stained with Prussian blue. The correct answer is D.

Explanation of Sideroblasts

Sideroblasts are erythroid precursors (normoblasts) in the bone marrow that contain visible iron granules in their cytoplasm. These iron-containing granules:

• Appear as bright-blue specks when stained with Prussian blue stain
• Represent iron that has been incorporated into the developing red blood cell but has not yet been utilized for hemoglobin synthesis
• Can be seen in normal erythropoiesis as part of iron utilization for hemoglobin production

Prussian Blue Stain

Prussian blue (also known as Perls' stain) is the specific histochemical stain used to identify iron in tissues:

• It reacts with ferric iron (Fe³⁺) to produce a bright blue color
• Is considered the gold standard for identifying iron deposits in bone marrow
• Is routinely used to assess iron stores in bone marrow biopsies 1

Distinguishing from Other Options

Let's examine why the other options are incorrect:

1. Siderocytes; Wright-Giemsa (Option A):

   • Siderocytes are mature red blood cells (not normoblasts) containing iron granules
   • While Wright-Giemsa is used for general blood cell morphology, it does not specifically highlight iron

2. Histiocytes; myeloperoxidase (Option B):

   • Histiocytes are tissue macrophages, not erythroid precursors
   • Myeloperoxidase stain identifies granulocytic cells, not iron

3. Reticulocytes; new methylene blue (Option C):

   • Reticulocytes are immature RBCs that have lost their nucleus
   • New methylene blue stains ribosomes and RNA remnants in reticulocytes, not iron

Clinical Significance

The identification of sideroblasts using Prussian blue stain has important clinical applications:

• Helps assess bone marrow iron stores
• Aids in diagnosing iron-related disorders such as:
  • Iron deficiency anemia (decreased or absent sideroblasts)
  • Sideroblastic anemias (increased number of abnormal ring sideroblasts)
  • Hemochromatosis (increased iron stores)

In normal bone marrow, approximately 20-40% of normoblasts may contain small iron granules (sideroblasts). When these iron granules form a ring around the nucleus (ring sideroblasts), it suggests pathological conditions like myelodysplastic syndromes or sideroblastic anemias 1.

Technical Considerations

When performing Prussian blue staining:

• Fresh samples yield optimal results
• The stain specifically reacts with ferric iron (Fe³⁺) to form ferric ferrocyanide
• The bright blue color makes iron deposits easily identifiable even at lower magnifications
• This technique is considered the gold standard for bone marrow iron assessment 1

Proper identification of sideroblasts using Prussian blue stain remains an essential component of bone marrow examination for evaluating disorders of iron metabolism and erythropoiesis.