Bone marrow analysis

Practical Application of Bone Marrow Aspiration and Its Interpretation Harold Tvedten Sweden WSAVA, 2001 INDICATIONS FOR BONE MARROW EVALUATION The basic indication for performing a bone marrow evaluation is to answer questions that a routine hematology examination of a blood sample does not answer. One need not take the additional effort to take a bone marrow aspirate and biopsy, if, forexample, the blood already clearly indicated an immune mediated hemolytic anemia, a typical inflammatory response, or even a leukemia with clearly diagnostic features in EDTA blood is present. The most common indications for bone marrow analysis are a deficiency of cells from one, two or all three cell lines. Cytopenias suggest decreased bone marrow function so one should check for various bone marrowdiseases. These would be a nonregenerative anemia, thrombocytopenia and/or leukopenia. Additionally, leukemia may be hidden in the marrow—blast cells may be numerous in the bone marrow but few or no blast cells are seen in the blood (aleukemic leukemia). Suggestions of leukemia are dysplastic changes such as megaloblastic rubricytes, hypersegmentation, or rare blast cells in the blood. Hypercalcemiamay be caused by lymphosarcoma, which may be located in the bone marrow. Plasma cell myeloma may be suggested by hyperproteinemia or by lytic lesions in the spine. BONE MARROW PROFILE A profile of tests allows the most complete evaluation and best conclusions. The profile should include a complete blood count (CBC), bone marrow aspirate, and bone marrow biopsy. The biopsy is often neglected butis especially important when evaluating cytopenia and when one expects low cellularity of the bone marrow. All too often, one has a poorly cellular aspirate of bone marrow where it is uncertain if the low cellularity of the sample reflects low cellularity of the bone marrow or a poor aspirate. A CBC gives excellent quantitative and morphologic information at the time of the bone marrow evaluation.An aspirate allows excellent morphologic evaluation of cells, differential count and myeloid:erythroid (M:E) ratio. A histologic section of a biopsy sample gives the best quantitative information on the cellularity of the marrow and reveals meylofibrosis and architectural patterns. All three together usually provide the best information possible. Neglecting one or two parts often leaves unansweredquestions. Performing a test several days after the other may also leave some questions.

ANSWERS FROM BONE MARROW EVALUATION The usual answers one gets from bone marrow aspirates and biopsy are quantitative, with morphologic information on the cell lines in the bone marrow. Typical answers include hypoplasia, hyperplasia or normal numbers of myeloid, erythroid, megakaryocytic and lymphoidcells. These changes are then interpreted in conjunction with the cell numbers seen in blood. Additional answers/conclusions/diagnoses are based on the maturity and appearance of the cells examined. Increased immaturity usually indicates a hyperplastic/reactive change unless extreme. Presence of over 30% blast cells indicates an acute leukemia. Hemosiderin amount helps diagnose iron deficiency anemia(absence) or anemia of inflammation (increased). When interpreting a bone marrow report or reading a smear oneself, the first decision should be whether the sample provided adequate cells of sufficient quality to be representative of the bone marrow. Always realize that one is interpreting changes from the norm in a sample and one must first determine if the sample represents the bone marrowadequately. The next factor is predicting the cellularity of the bone marrow. Cellularity is best predicted by particles on an aspirate or by a histologic section. Cellularity of individual cells may be so dense as to also indicate normal to increased cellularity of the bone marrow. A differential count gives the percentage of various cell types, which when compared to the estimate of total...