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Describe the indications, sites and interpretation of bone marrow examination.

Pathology · 2nd Professional — Para-Clinical

Indications

Bone marrow examination comprises aspiration, which gives cellular detail, and trephine biopsy, which gives architecture and cellularity.

Category	Indications
Diagnostic	Leukaemia, lymphoma, myeloma, aplastic anaemia, myelodysplasia, myelofibrosis
Unexplained cytopenias	Pancytopenia, isolated thrombocytopenia or neutropenia, leucoerythroblastic blood picture
Assessment of iron stores	The gold standard for iron deficiency; also sideroblastic anaemia
Infection	Kala-azar (leishmaniasis), miliary tuberculosis, pyrexia of unknown origin
Staging	Lymphoma, neuroblastoma, small cell carcinoma
Monitoring	Response to chemotherapy; remission status

Sites and Technique

Site	Use
Posterior superior iliac spine	The site of choice in adults — safe, ample marrow, allows both aspirate and trephine
Sternum (2nd or 3rd intercostal space)	Aspiration only — trephine is dangerous; risk of cardiac and great vessel injury
Anterior superior iliac spine	Alternative in adults
Upper end of tibia	Infants under 18 months only

Aspirate and trephine are complementary — the aspirate shows cytology, the trephine shows cellularity, architecture, fibrosis and infiltration
Contraindications — there are almost none; even severe thrombocytopenia is not a bar, since pressure controls the bleeding. Haemophilia requires factor cover

What Is Assessed

Cellularity — the proportion of haemopoietic tissue to fat; roughly 100 minus the age as a percentage in adults
Myeloid:erythroid ratio — normally about 3:1; reversed in haemolysis and megaloblastic anaemia
Maturation of each series, and the proportion of blasts
Megakaryocytes — number and morphology
Abnormal cells — blasts, plasma cells, lymphoma cells, metastatic carcinoma, granulomas, parasites
Iron stores by prussian blue — storage iron in macrophages and ring sideroblasts

CLINICAL PEARL

A "dry tap" is itself a finding, not a failure. When nothing can be aspirated, the marrow is usually fibrotic or packed — myelofibrosis, hairy cell leukaemia, extensive infiltration, or aplastic anaemia. It is precisely then that the trephine is essential, and repeating the aspiration elsewhere wastes time.

Applied Aspects

Always make films at the bedside — marrow clots within seconds, and a clotted specimen is useless
Send material for the right investigations — morphology, flow cytometry, cytogenetics, molecular studies and culture; deciding afterwards is too late
In India, marrow aspiration is a key test for kala-azar, showing Leishman–Donovan bodies within macrophages, and for disseminated tuberculosis
The trephine must be adequate — at least 1.5–2 cm of intact core, since a crushed or subcortical sample cannot be interpreted
Complications are rare — bleeding, infection and pain; sternal puncture has caused fatal cardiac tamponade and should be used only when necessary

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