A Comparative Study of Bone Marrow Squash and Wedge Aspiration Smears

Bone marrow examination entails study of aspirate smears, touch imprints and trephine biopsy. Bone marrow aspirate smears can be prepared by the squash (crush) or wedge method. Both techniques have their own advantages and disadvantages. There is paucity of studies that have compared these smear types. This study was conducted over a period of one year. Two hundred and five bone marrow aspirates were included. Both squash and wedge smears were made. Blinded slide review was done. Bone marrow cellularity, megakaryocyte number, myeloid to erythroid (M:E) ratio, morphology and final diagnosis on each smear type was compared. Chi square test, t-test and Kappa were applied to study the agreement between the wedge and squash smears. Among the 205 patients studied, squash smears showed significant over estimation of cellularity and megakaryocyte number (p < 0.05). There was no significant difference (p > 0.05) in the M:E ratio and morphological scores. Most patients (188/205 [91.7%]) showed complete diagnostic concordance while 17 (8.3%) patients had discrepancy in diagnosis between the squash and wedge smears. In 8 (3.9%) of these, major discrepancies were seen while 9 (4.4%) patients had minor discrepancies. Bone marrow cellularity and megakaryocyte numbers were underestimated in wedge smears with no differences in M:E ratio or morphology. Acceptable agreement for diagnosis was seen for patients with most disorders. Major diagnostic discrepancies were seen in patients with lesions known to have focal distribution-lymphoma, myeloma and tuberculosis (granulomas). Both squash and wedge smears should be studied for bone marrow examination.