Bone Marrow Evaluation and Hematopoiesis

The process of blood cell formation, primarily occurring in bone marrow.

Blood cell production outside bone marrow, mainly in the spleen and liver.

Granulocytes, monocytes, erythrocytes, and megakaryocytes/platelets.

B cells, T cells, plasma cells, macrophages, mast cells, osteoclasts, fibrocytes, and adipocytes.

It may reveal abnormalities suggesting marrow disease, but cannot always confirm the diagnosis or extent.

Persistent, unexplained hematologic abnormalities, especially cytopenias.

Persistent, unexplained nonregenerative anemia; marrow can also assess erythroid regeneration in horses.

Unexplained neutropenia without a left shift or persistent thrombocytopenia.

Bicytopenia is decreased counts in two blood cell lines; pancytopenia affects all three major lines.

Persistent or extreme increases in WBCs, RBCs, or platelets.

They may indicate primary hematopoietic neoplasia, especially without enlarged lymphoid organs.

To confirm leukemia, determine cell lineage, and assess normal hematopoiesis for prognosis and treatment.

To determine marrow involvement and disease extent; marrow involvement worsens lymphoma prognosis.

Hypercalcemia and hyperglobulinemia, especially monoclonal gammopathy associated with plasma cell neoplasia.

Histoplasmosis and leishmaniasis because the organisms may be present in marrow.

Storage diseases cause abnormal cellular accumulation; iron deficiency causes decreased stainable iron.

Decreased in iron deficiency, increased in chronic inflammation, and normally not stainable in cats.

Regenerative anemia and nonextreme neutrophilia or erythrocytosis.

Lymphocyte numbers depend mainly on secondary lymphoid tissues and lymphocyte distribution.

Marrow findings must be interpreted alongside current peripheral blood findings.

active hematopoietic tissue (flat bones, end of long bones)

Excellent individual-cell detail and maturation assessment; relatively inexpensive and rapid.

Better assessment of overall cellularity, architecture, fibrosis, necrosis, and focal infiltrative disease.

Aspiration can miss focal disease; biopsy is slower, more expensive, and provides less cellular detail.

They provide complementary information about individual cells and overall tissue architecture.

Sample adequacy, cellularity, megakaryocytes, lineage maturation/morphology, G:E ratio, other cells, and iron stores.

Presence of marrow unit particles; without particles, cellularity cannot be reliably assessed.

By evaluating the proportion of hematopoietic cells versus fat within unit particles.

Young 75 cells:25 fat, adults 50:50, and old animals 25:75.

More than 90%.

Increased cell production due to demand or infiltration by foreign/neoplastic cells.

Decreased production in one or more lineages, potentially due to drugs, toxins, infection, or immune-mediated disease.

Hyperplasia = increased normal cells; hypoplasia = decreased cells; aplasia = absence of hematopoietic cells.

Erythroid hypoplasia with granulocytic hyperplasia.

Large platelet-producing precursor cells; approximately 2–4 per particle.

Megakaryocytes associate with unit particles, so an inadequate sample may miss them.

Megakaryocytic hyperplasia, sometimes with increased immature megakaryocytes.

An appropriate marrow response to peripheral platelet destruction or consumption, especially ITP.

Approximately 1–1.5:1.

Meaning that for every 1 to 3 granulocytic cells, you
should see 1 to 2 erythroid cells

An abnormal ratio may reflect increased production of one lineage or decreased production of the other.

Marked granulocytic hyperplasia and marked erythroid hypoplasia.

Cells progress normally from immature precursors to mature blood cells.

Less than 5% in most species, but up to 15% in healthy cats.

Aging, immune stimulation, or neoplasia such as multiple myeloma.

Store iron and support erythroid development; increase with inflammation, immune-mediated disease, and histiocytic disorders.

Aplastic anemia, mast cell neoplasia, or inflammation.

Neutropenia first, then thrombocytopenia, then anemia.

Loss of all three major marrow cell lines; causes include immune-mediated disease, viruses, drugs, estrogen toxicity, irradiation, Ehrlichia, and bracken fern.

Necrosis may follow toxins, drugs, DIC, hypoxia, viruses, or immune disease; myelofibrosis indicates chronic marrow injury.

Replacement of normal marrow by neoplastic cells, usually leukemia or metastasis; abnormal cells dominate while normal blood cell production decreases.