Bone marrow is a semisolid tissue present in all the bones divided schematically into hematopoietically inactive fatty marrow, named yellow marrow, and hematopoietically active marrow, named red marrow. In adults, red marrow is mainly found in the central skeleton such as pelvis, sternum, skull, vertebra, scapulae, as well as epiphyseal areas of long bones such as femur and humerus.
The function of hematopoietic marrow is to regulate myeloid and lymphoid cell trafficking as well as hematopoietic stem and progenitor cell maintenance for normal myelopoiesis and lymphopoiesis. In addition, the marrow contains mesenchymal stem cells that can differentiate into adipocytes, hepatocytes, osteoblasts, chondrocytes, skeletal, and cardiac muscle cells. The nonhematopoietic marrow serves as a large store of reserve lipids. Bone marrow endothelial cells form a barrier preventing entry of red blood cells and platelets from the circulation regulating cell trafficking and osteogenesis. These cells also contribute to specialized perivascular microenvironment where majority of hematopoietic stem cells are present.
The total mass of an adult bone marrow is estimated between 1600 g and 3700 g.
Macroscopy and Techniques for Studying the Marrow
Evaluation of bone marrow benefits both from thoroughly cytological evaluation by aspirate smear preparations (usually sternal for individuals older than 12 or the pelvic bone) as well as histopathological evaluation by bone marrow trephine biopsy (BMB) (usually posterior superior iliac spine) for evaluation of the architecture, cellularity, focal lesions, fibrosis, or necrosis.
Bone marrow aspirate provides liquid sample with mixed cell population of bone marrow cells. After bone marrow harvest, high quality smears are realized onto glass slide, air-dried and stained using May Grünwald Giemsa. Complementary cytochemistry staining can be done such as Perls staining to see intracellular (erythroblastic) and extracellular iron distribution. Sometimes, myeloperoxidase or esterase staining are useful to better characterize abnormal leukemic cells.
Bone marrow trephine biopsy provides a core of cortical and medullary areas which contain bone trabeculae and hematopoietic tissue. It is optimally a cylinder of 1.5–2 cm length. This biopsy is sent usually in the laboratory of pathology in 10% neutral buffered formalin. European Bone Marrow Working Group promotes slow decalcification using EDTA during 48 h, allowing perfect epitope conservation for immunohistochemistry and fairly good nucleic acid preservation for molecular evaluation (NGS, lymphoid clonality tests, …). Slides of 2–3 μ thickness should be prepared and stained with H&E, Giemsa (crucial for cytological evaluation), Perls for hemosiderin deposits, silver impregnation for fibrosis. When fibrosis is diagnosed on H&E, a trichrome stain is recommended. PAS stain is sometimes used, for example, to better evaluate megakaryocytes as well as immunoglobulin within lymphocytes with plasma cell differentiation.
Cytology on a Marrow Aspirate
Bone marrow aspirate should always be analyzed together with peripheral blood film observation.
2014 Reference values of normal adult bone marrow according to the French Society of Hematology
Reference range (%)
Blasts/stem cell/undifferentiated cell
(Segmented and band) neutrophils
(Segmented and band) eosinophils
(Segmented and band) basophils
Acidophilic (orthochromatic) erythroblast
In conclusion, bone marrow cytological examination is the best way to study the quantitative and qualitative constitution of hematopoietic system but must be associated in some cases to histological examination depending on the context (to look for presence of fibrosis, for a diagnosis of Aplastic anemia, in case of focal lesions or unexplained fever….).
Histopathology on BMB
Multiparametric flow cytometry evaluation of bone marrow is a very useful complement to quantify and characterize normal or pathologic hematopoietic cells.
All hematopoietic cells express the panleucocyte antigen CD45, except erythroblastic cells that are positive for CD36 and Glycophorine A.
Immature cells (blast cells) underexpress CD45 and may be also positive for CD34, TdT, and/or CD117 antigen.
Lymphocytes cells of B lineage are characterized by CD19, CD20, CD22, CD79a, CD79b, and CD10 expression. Lymphocytes cells of T lineage are characterized by intracytoplasmic and membrane CD3 expression and CD5, CD7, CD2, CD4, or CD8 expression.
Myeloid cells are positive for CD13, CD33, CD117, and CD15 antigens. Monocytic cells show a weak expression of CD4 and are CD14 and CD36 positive.
Megakaryoblasts can be characterized by CD61 and CD42 antigen expression.
Immunohistochemistry on Paraffin-Embedded Tissues
CD34: blasts and endothelial cells
Myeloperoxidase, CD15, CD33: maturing granulocytes
CD68 (KP1) with some staining of granulocyte lineage, CD68 (PGEM1), CD163: macrophages
CD14: monocytes (subpopulation)
Glycophorin A, Glycophorin C, CD71: erythroblastic lineage
Fact VIII, CD61: megakaryocytes
CD117: mastocytes, proerythroblast, early promyelocyte, blasts
TdT: lymphoid blasts, hematogones
CD20, PAX5: B lymphocytes
CD79a: B lymphocytes and plasma cells
CD138: plasma cells, (metastatic carcinoma may be CD138+)
CD3, CD4, CD5, CD7, CD8; T lymphocytes
IgA, G, M, K, L: immunoglobulin heavy and light chains
Table with Important Diseases (Links)
Affected by diseases like
Infection (tuberculosis, atypical mycobacterial infection, leishmaniosis, …) and inflammatory diseases
Myeloproliferative neoplasms: chronic myeloid leukemia BCR-ABL1 positive, essential thrombocythemia, polycythemia vera, primary myelofibrosis
Myelodysplastic syndromes/myeloproliferative neoplasms
Plasma cell myeloma
T-cell large granular lymphocytic leukemia
References and Further Reading
- Itkin, T., Gur-Cohen, S., Spencer, J. A., Schajnovitz, A., Ramasamy, S. K., Kusumbe, A. P., Ledergor, G., Jung, Y., Milo, I., Poulos, M. G., Kalinkovich, A., Ludin, A., Kollet, O., Shakhar, G., Butler, J. M., Rafii, S., Adams, R. H., Scadden, D. T., Lin, C. P., & Lapidot, T. (2016). Distinct bone marrow blood vessels differentially regulate haematopoiesis. Nature, 532, 323–328.CrossRefGoogle Scholar
- Kroft, S. H. (2012). Bone marrow. In S. E. Mills (Ed.), Histology for pathologists (4th ed., pp. 849–887). Philadelphia: Lippincot Williams and Wilkins.Google Scholar
- Swerdlow, S. H., Campo, E., Harris, N. L., Jaffe, E. S., Pileri, S. A., Stein, H., & Thiele, J. (2017). WHO classification of tumours of haematopoietic and lymphoid tissues (4th ed.). Lyon: International Agency for Research in Cancer.Google Scholar