Approach to Bone Marrow Aspiration : Cases with Discussion | Part 1/2

Approach to Bone Marrow Aspiration : Cases with Discussion | Part 1/2
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Assessing and reporting bone marrow films
Unless a very recent blood count and film is available a venous blood sample should be obtained at the same time as the bone marrow aspirate. A blood film should already have been examined carefully in the prebiopsy assessment of the patient but should be examined again as part of the assessment of the bone marrow aspirate. A reticulocyte count, performed on the day of the bone marrow aspiration, can be useful—particularly for determining whether erythroid hyperplasia is associated with effective or ineffective erythropoiesis. The films should first be examined under low power (×10 objective) to assess the number of fragments, the cellularity, and the number of megakaryocytes, and also to detect any low incidence abnormal cells such as carcinoma cells. The films should then be examined in detail using a ×40 or ×50 objective. There should be a systematic assessment of the cellularity and contents of fragments, megakaryocyte number, and morphology and cytological features of other lineages. Fine cytological details should be assessed using an oil immersion ×100 objective. A differential count should be performed in the trails behind several fragments because this will be the part of the film minimally diluted by peripheral blood. At a minimum, several hundred cells should be counted, with the granulocyte and erythroid series, lymphocytes, and plasma cells being enumerated and a myeloid to erythroid cell ratio being calculated. Depending on the indication for the bone marrow aspiration, this may be all that is required. For example, a more detailed differential count would not be required if the bone marrow features were those of iron deficiency or megaloblastic anaemia. However, if the features were those of acute leukaemia or a myelodysplastic syndrome a 500 cell differential count should be performed, and all cell types should be enumerated. Similarly, if the features were those of multiple myeloma with 80% of myeloma cells being present, a detailed differential count would not be necessary. However, if myeloma or MGUS was suspected but the number of plasma cells was only moderately increased, 500 cells should be counted and the count should include several different bone marrow films. A focal increase in cells of one particular lineage should be noted. Both blast cells and myeloma cells are sometimes irregularly distributed so that a differential count should be performed in the area where abnormal cells are most numerous. The report might then read—for example, “overall plasma cells are 10% of bone marrow cells but in the trails behind several fragments they comprise 30–40% of cells”. The quantitative and qualitative assessment of cells in Romanowsky stained films should be followed by assessment of the iron stain and any cytochemical stains. If stainable iron is absent from fragments but there are only small numbers of fragments available for assessment this should be noted. The report might read—for example, “no storage iron detected but only one fragment available for assessment”.
The report of the bone marrow films should include the clinical details, the major features of the blood count, the results of blood film examination, and the bone marrow findings. It is useful to include the white cell count, haemoglobin concentration, platelet count, mean cell volume, and reticulocyte count as a routine, but in selected patients other important blood count abnormalities should be recorded. The report should then include details of the aspiration procedure, specifically the site of aspiration, whether aspiration was easy or difficult, and whether or not bone texture was normal. The report on the bone marrow films should differentiate factual statements from opinion. The body of the report should include an assessment of cellularity and a systematic description of each lineage. The myeloid to erythroid cell ratio and the salient features of the differential count should be given. The report should include a list of other investigations that have been performed—for example, “trephine biopsy and immunophenotyping to follow”, so that clinical staff are aware of any investigations that are still pending. Finally, the report should have a summary or conclusion in which it is appropriate to express an opinion and, if necessary suggest further tests. If it is possible to make a definite diagnosis this should be done.