Bone Marrow Examination
On this page
Direct answer
Read together, the aspirate and the trephine biopsy answer two different questions: the aspirate spreads individual cells for cytological detail — maturation, dysplasia, blasts, parasites and storage deposits — while the trephine preserves architecture, revealing cellularity, fibrosis, granulomas and metastatic carcinoma that aspiration alone can miss. Both are taken from the posterior superior iliac crest in adults (the anterior tibial site in infants under about one year), reported with a myeloid-to-erythroid ratio of roughly 3:1 (accepted range 2-4:1) and blasts below 5 per cent of nucleated cells. A dry or heavily blood-diluted tap is itself a finding, pointing towards aplastic anaemia, myelofibrosis or hairy cell leukaemia rather than technical failure.
What you must remember
- What a complete study contains: aspirate smears, touch imprints from the trephine, a formalin-fixed core at least 1.5-2 cm long, plus aspirate allotted to flow cytometry, cytogenetics and molecular studies before staining.
- Core numbers: M:E ratio 2-4:1; blasts under 5 per cent; megakaryocytes scattered singly without clustering; cellularity judged against the age rule of thumb (100 minus age per cent).
- Histochemical stains: myeloperoxidase and Sudan black for myeloid lineage, periodic acid-Schiff (block positivity in precursor B-ALL), Perls' Prussian blue for iron and ring sideroblasts, tartrate-resistant acid phosphatase for hairy cell leukaemia, reticulin for fibrosis.
- Dry tap causes to recite: aplastic anaemia, myelofibrosis, hairy cell leukaemia — a haematology-oncology triad examiners quote verbatim.
- Cellularity logic: hypercellular marrow in haemolysis, megaloblastic anaemia, acute leukaemia and CML; hypocellular in aplastic anaemia, hypoplastic MDS and after chemotherapy.
- Storage cells: Gaucher cells with crumpled-tissue-paper cytoplasm; Niemann-Pick cells foamy and oil-red-O positive — seen in the aspirate of children with hepatosplenomegaly.
- Metastatic deposits: breast, lung, prostate, thyroid and kidney top the list; cohesive epithelial nests in a desmoplastic stroma, frequently associated with a leukoerythroblastic peripheral smear.
Where candidates slip
The classic error is trusting a normal aspirate in myelofibrosis or metastatic disease: fibrous stroma anchors the abnormal cells, and aspiration samples only what it can pull free, so the trephine is the definitive specimen. The second slip is grading iron on a decalcified core — acid decalcification dissolves haemosiderin, so Perls' stain belongs on the aspirate smears. Third, a dry tap in hairy cell leukaemia should push the diagnosis to peripheral-blood flow cytometry (CD11c, CD25, CD103, annexin A1), because the marrow is packed and fibrotic, not empty; conflating "dry" with "aplastic" in this disease is a viva-ending move.
Frequently asked questions
Which site is used for marrow aspiration in adults and in infants?
The posterior superior iliac crest in adults and older children; the anterior tibial tuberosity or upper tibia in infants under about one year.
What is the normal myeloid-to-erythroid ratio?
About 3:1, with an accepted range of 2-4:1; it rises in infection and chronic myeloid leukaemia and falls in haemolysis and megaloblastic anaemia.
Name three conditions that produce a dry tap.
Aplastic anaemia, myelofibrosis and hairy cell leukaemia are the standard triad; heavy metastatic infiltration can also block aspiration.
Which stain identifies ring sideroblasts and why must it be on the aspirate?
Perls' Prussian blue on aspirate smears, because acid decalcification of the trephine core leaches out iron and underestimates stores.
What is a leukoerythroblastic picture and what does it suggest?
Nucleated red cells and immature granulocytes in the peripheral smear, classically indicating marrow replacement — metastasis, myelofibrosis or severe marrow stress.
Which stain supports hairy cell leukaemia on aspirate smears?
Tartrate-resistant acid phosphatase positivity, although flow cytometry on blood (CD11c, CD25, CD103) is the modern mainstay.