Iron Staining in the Bone Marrow Biopsy

 

Stain required:

(1) iron stain (Perls's, Prussian blue)

(2) usually on bone marrow smears, clot sections and core biopsy

 

Assessment:

(1) Processing, especially decalcification, can reduce the amount of iron seen in clot sections and core biopsy. The smears tend to be most sensitive and core biopsy least sensitive. However, all 3 preparations need to be examined, as iron can be seen in one preparation but not in the others.

(2) Extracellular stores can be confused with artifact ; grading should not be based solely on extracellular stores. Intracellular stores should always be included in the evaluation.

(3) Most of the intracellular iron stores are in macrophages, with small amount in erythroblasts (sideroblasts)

(4) The grade of iron stores correlates with chemical analysis of micrograms iron per gram tissue (semilogarithmic)

Grading of bone marrow storage iron	Grade
no stainable iron	0
small iron particles just visible in reticulum cells using an oil objective	1+
small, sparse iron particles in reticulin cells, visible at lower power	2+
numerous small particles in reticulum cells	3+
larger particles with a tendency to aggregate into clumps	4+
dense, large clumps	5+
very large clumps and extracellular iron	6+

 

Interpretation:

• normal iron stores: 1+, 2+, 3+

• iron deficiency: 0

• increased iron stores: 4+, 5+, 6+

 

Sideroblasts are erythroblasts with fine iron-containing granules in the cytoplasm.

(1) Normal sideroblasts show random iron deposits (typically 1-5) in the cytoplasm.

(2) Normal patients with normal iron stores will have 20-50% of marrow erythroblasts as sideroblasts.

(3) Ringed sideroblasts are abnormal sideroblasts with increased granular iron deposits in the cytoplasm forming a ring around the nucleus.