Role of bone marrow aspiration clots for evaluating cellularity: comparison of clots, biopsies, and smears

Abstract

In bone marrow (BM) analysis, cellularity provides important information for evaluating hematopoiesis and hematological disease status. BM cellularity is usually assessed using BM biopsy sections. It can also be evaluated using BM aspiration smears if a biopsy is not performed. BM aspiration clots are not routinely used to evaluate BM cellularity at some hospitals [1]. Here, we evaluated the relationships among the BM cellularity values obtained using BM biopsy sections, aspiration smears, and aspiration clots. We retrospectively examined the cases of 114 consecutive patients who underwent BM examinations to obtain new diagnoses between January 2019 and January 2021 at our institution. All three types of BM evaluation produced valuable results in 57 patients. There were no differences in disease type between the patients who did and did not undergo all three types of BM examination (Supplementary Table S1). Therefore, the 57 patients were analyzed in this study. The cellularity of BM biopsies and clots was classified into 5% increments. The cellularity of BM smears was assessed based on the nuclear cell count (NCC). The correlations between the cellularity values of biopsies and clots/smears were analyzed using the Spearman rank correlation test. All statistical analyses were performed using GraphPad Prism 9 (GraphPad Software Inc., San Diego, CA). The patients’ median age was 78 years. Their diseases, which included myelodysplastic syndrome (MDS), are shown in Supplementary Table S2. The patient with MDS with excess blasts-2 also had myelofibrosis (MF-2 according to the World Health Organization histological grading system). No myelofibrosis was observed in the other patients, including those with myeloproliferative neoplasms. In the malignant lymphoma patients, there was no evidence of lymphoma cells being present in the BM. The cellularity of BM biopsies and clots were significantly correlated (Fig. 1a). The correlation between the cellularity of BM biopsies and smears was weaker than that between the cellularity of BM biopsies and clots (Fig. 1b). The correlation between BM biopsies and smears was especially weak when the NCC was < 100,000 cells/μL (Fig. 1c). In cases of MDS with NCC of < 400,000 cells/μL, in which cell density affects the clinical course of MDS, there was no correlation between the cellularity of BM biopsies and smears (Fig. 1d). A previous study demonstrated discrepancies between the cellularity values of BM clots and smears, especially in lymphoproliferative disorders [2]. BM clots were reported to be more useful than BM smears for assessing lymphoma cell involvement and the percentage of plasma cell infiltration in multiple myeloma [3, 4]. Recently, BM biopsy devices have improved, but no subsequent studies have compared the BM cellularity values obtained from biopsies, clots, and smears. BM smears are generally considered to be sufficient for diagnosing MDS [5]. However, our study suggests that it is important to assess BM cellularity using clots if a biopsy is not performed. A previous study showed that BM cellularity was reduced in 18% of healthy individuals [6]. Our study also indicated that clot analysis is valuable for low-NCC samples. Thus, BM clot examinations are useful and can be conducted during the same procedure as smears. * Hiroki Hosoi [email protected]