Evaluation of bone marrow aspirate smears

INTRODUCTION — Aspiration and biopsy of the bone marrow is used to diagnose, confirm, and/or stage hematologic disease, and is a diagnostic tool in non-hematologic disorders (eg, storage disease, systemic infection) and malignancies. It is an ambulatory procedure performed under local anesthesia, with low morbidity.

The evaluation of bone marrow aspirate smears will be discussed here.

Details of the bone marrow aspirate and biopsy procedure, additional testing performed on the bone marrow, and complications of the procedure are discussed separately. (See "Bone marrow aspiration and biopsy: Indications and technique".)

Evaluation of the peripheral blood smear is also covered separately. (See "Evaluation of the peripheral blood smear".)

SAMPLE PREPARATION — As described separately, the clinician performing the procedure should check with the hematopathology laboratory prior to the procedure for clarification about slide preparation and collection of additional specimens for cytogenetics, immunologic studies, and/or cultures, as well as guidance concerning timely evaluation of the collected material by the clinician and the hematopathologist. It is often helpful to have another person at the procedure to help make the aspirate smears before the sample forms a clot. (See "Bone marrow aspiration and biopsy: Indications and technique", section on 'Preparation of samples'.)

Staining — There are many different techniques for preparing marrow aspirate smears in order to assure that there is adequate cellularity and good morphology. Most laboratories employ Wright-Giemsa staining to highlight nuclear and cytoplasmic characteristics.

Special stains may be employed to determine clonality (eg, immunoglobulin light chains), presence of reticulin or collagen (eg, silver and trichrome stains), presence of amyloid (eg, Congo red staining), iron stores and/or iron-containing ring sideroblasts typical of some myelodysplastic syndromes (eg, Prussian blue staining), as well as stains for the presence of various infectious agents.

The dry tap — On occasion, marrow aspiration is not successful, resulting in what has been called a "dry tap." There are a number of possible reasons for this; the most common cause is that the tip of the aspiration needle is not within the marrow cavity. Cautious advancement of the needle, or reinsertion into an adjacent site usually suffices if this is the problem.

In other cases, the bone marrow cavity may have been entered, but little or no material can be aspirated, either because marrow cellularity is severely reduced (eg, aplastic anemia, bone marrow necrosis [see below]), or the bone marrow is intensely hypercellular (eg, leukemia, lymphoma) or fibrotic (eg, myelofibrosis, hairy cell leukemia), thus resisting attempts at aspiration.

If a true dry tap occurs, bone marrow biopsy should be performed. Touch preparations can be made by rolling the biopsy specimen on glass slides. This will often result in sufficient additional material becoming available for diagnostic evaluation [1]. (See "Bone marrow aspiration and biopsy: Indications and technique", section on 'The dry tap'.)

Bone marrow necrosis — Uncommonly, aspiration of the bone marrow cavity at one or more sites may yield necrotic material with cells having indistinct cellular outlines and smudged nuclei, surrounded by amorphous eosinophilic material [2-4]. The most common causes of this finding are bone marrow infarction during or following a vaso-occlusive crisis involving marrow-containing bone in sickle cell disease and marrow infiltration with malignant cells, often of hematopoietic origin [5-10]. (See "Acute and chronic bone complications of sickle cell disease".)

Other reported causes include direct damage to bone (eg, radiation, trauma, decompression sickness, aseptic necrosis), infection (HIV, tuberculosis, paracoccidiomycosis, typhoid fever, septic shock), and lupus erythematosus (table 1) [10-14]. Affected patients often complain of fever and bone pain [5,6]. Common laboratory findings include circulating nucleated red cells, thrombocytopenia, anemia, and elevated serum levels of lactate dehydrogenase and alkaline phosphatase [5].

Gelatinous degeneration of the marrow with serous fat atrophy and varying degrees of cytopenia has been described in patients with anorexia nervosa. (See "Anorexia nervosa in adults and adolescents: Medical complications and their management", section on 'Hematologic'.)

LOW POWER EXAMINATION OF THE MARROW — Bone marrow smears are first examined under low power magnification to look for the presence of the following:

●Adequacy of the sample (see 'The dry tap' above and 'Bone marrow necrosis' above)

●Presence or absence of cellular monotony

●Presence or absence of large cells, clumps of tumor cells, or storage cells

●Presence or absence of bone marrow spicules

●Ratio of fat to overall cellularity

As an example of the above, one might be struck by the monotony of the cell population, such as might be seen in a patient with acute lymphocytic leukemia (picture 1) or chronic prolymphocytic leukemia (picture 2).

Large cells — The largest cells one will normally see in a bone marrow aspirate are megakaryocytes, the immediate precursor of circulating platelets (picture 3A-B). Other large cells that are seen only under abnormal circumstances include:

●Reed-Sternberg cells in patients with Hodgkin lymphoma (picture 4)

●Giant, bizarre malignant plasma cells in multiple myeloma (picture 5)

●Giant early red cell precursors (proerythroblasts) in acquired pure red cell aplasia as seen after infection with parvovirus B19 (picture 6)

Cells in clumps or clusters — The appearance of large clumps of cells scattered about, often at the sides or end of the smear, with indistinct cellular borders, might turn out to be metastatic cancer. Such clumps may be relatively amorphous (picture 7) or might form rosette-like structures as in metastatic neuroblastoma (picture 8). One might also see clumps or sheets of malignant plasma cells in multiple myeloma (picture 5), or a benign finding such as a clump of osteoblasts (picture 9).

Storage cells — Unusual clusters of large cells seen on low-power scanning may be storage cells, which on higher power may reveal the presence of macrophages (histiocytes) with voluminous cytoplasm, containing undigested lipids. These may include the storage cell of Gaucher's Disease, a macrophage containing cerebrosides and creating a typical striated appearance to the cytoplasm (picture 10) (see "Gaucher disease: Pathogenesis, clinical manifestations, and diagnosis") or Niemann-Pick cells, macrophages containing sphingomyelin, with a characteristic foamy appearance of the cytoplasm (picture 11). (See "Neuropathies associated with hereditary disorders", section on 'Niemann-Pick disease'.)

Storage cells containing hexagonal, non-staining crystals may be seen in patients with the lysosomal disease, cystinosis [15]. (See "Cystinosis".)

Macrophages (histiocytes) with ingested cells or debris — Bone marrow macrophages (histiocytes) may have ingested blood cells, debris, or invading organisms, as follows:

●Blood cells – Increased numbers of otherwise normal-appearing macrophages which have ingested mature red cells, normoblasts, platelets, and/or neutrophils (picture 12) are seen in the hemophagocytic syndrome, often seen after viral infections, such as Epstein-Barr virus infection. (See "Clinical features and diagnosis of hemophagocytic lymphohistiocytosis", section on 'Bone marrow evaluation' and "Clinical manifestations and treatment of Epstein-Barr virus infection", section on 'Hemophagocytic lymphohistiocytosis'.)

●Debris – Normal-appearing macrophages may also contain debris-like material, such as ingested apoptotic tumor cells (ie, tingible body macrophages as seen in highly aggressive lymphomas), melanin-containing granules in a patient with melanoma metastatic to bone marrow [16], or crystals in patients with cystinosis [15]. (See "Epidemiology, clinical manifestations, pathologic features, and diagnosis of Burkitt lymphoma", section on 'Morphology'.)

●Digested material (sea blue histiocytes) – Sea blue histiocytes are marrow macrophages containing sea-blue-colored material, and are often seen following degradation of complex lipids, such as those seen in hyperlipidemia and lysosomal disease (eg, Niemann-Pick and Gaucher disease). These cells may also be seen in a variety of other conditions such as chronic myeloid leukemia, myelodysplasia, severe congenital neutropenia, lymphoma, and following hyperalimentation [17-20]. The sea blue histiocyte syndrome is a rare congenital disorder associated with massive accumulation of sea blue histiocytes along with abnormal liver function often leading to cirrhosis, splenomegaly, and lymphadenopathy [21]. Its etiology is unclear. (See "Overview of Niemann-Pick disease", section on 'Diagnosis of NPD-C' and "Clinical manifestations and diagnosis of chronic myeloid leukemia", section on 'Bone marrow biopsy'.)

●Invading organisms – Marrow macrophages may contain ingested infectious agents, such as histoplasma and cryptococcal organisms [22,23].

Estimation of cellularity and myeloid to erythroid ratio — After a thorough scanning under low and intermediate power, one can estimate overall bone marrow cellularity, which should be in the range of 40 to 60 percent in normal adults, with a somewhat lower range in older adult patients. A rough guide to the normal decline in cellularity with age is given by the following:

Bone marrow cellularity (%)  ≈  100  -  age (years)

Optimally, bone marrow cellularity is estimated from a bone marrow biopsy specimen (picture 13), but cellularity can often be estimated on an aspirate provided that it is performed in an area containing marrow spicules (picture 14).

Greater than 60 percent cellularity on the bone marrow biopsy suggests hypercellularity, while under 30 to 40 percent implies hypocellularity, as may be seen in idiopathic aplastic anemia (picture 15), in the hypocellular variant of myelodysplastic syndrome, or if the biopsy was performed in an area that had recently received high-dose radiation therapy.

The myeloid to erythroid ratio (M:E ratio) can also be estimated under scanning power (picture 16); it is normal to observe approximately three to four cells of the myeloid line for every cell in the erythroid line (ie, a M:E ratio between 3:1 and 4:1).

●The M:E ratio is typically increased in chronic myeloid leukemia, due to an absolute increase in cells of the granulocyte series (picture 17), and in pure red cell aplasia, due to an absolute decrease (or absence) of red cell precursors.

●The M:E ratio is most frequently decreased when erythroid hyperplasia is present, as seen in acute or chronic hemolysis (picture 18), or in the presence of drug-induced agranulocytosis, due to the specific loss of cells of the granulocyte series.

HIGH POWER EXAMINATION OF THE MARROW — The normal marrow aspirate shows a heterogeneous population of cells, with normal myeloid and erythroid maturation and a scattering of adult lymphocytes (picture 16).

The myeloid series (figure 1) normally matures from a myeloblast (picture 19) to promyelocyte (picture 20) to myelocyte (picture 21) to metamyelocyte (picture 22) to a band form (picture 23) and then an adult neutrophil (picture 24) (see "Regulation of myelopoiesis", section on 'Neutrophil production and maturation'). At the blast level, the nuclear to cytoplasmic ratio is very high and the scant cytoplasm is deep blue. As the cells mature, the nuclear chromatin starts to condense and invaginate and the cytoplasm develops the granulation typical of a mature neutrophil.

Erythroid cells mature from an erythroblast to a series of normoblasts referred to as basophilic, polychromatophilic, and orthochromic normoblasts (picture 25). As these cells become more mature, the nucleus condenses, and the cytoplasm gradually takes on the pinkish appearance of hemoglobin. (See "Regulation of erythropoiesis".)

In contrast to the marrow with a normal M:E ratio of approximately 3-5:1, there can be the presence of myeloid hyperplasia (eg, high M:E ratio), as seen in chronic myeloid leukemia (picture 17) or erythroid hyperplasia (eg, low M:E ratio), as seen in hemolytic anemias (picture 18).

Megaloblastic changes — Deficiencies of vitamin B12 or folic acid result in varying degrees of pancytopenia (ie, anemia, neutropenia, and thrombocytopenia) along with a hypercellular marrow with maturation abnormalities in both the myeloid and erythroid series. Not only are these cells larger than normal, but there is more open chromatin in the nucleus, creating megaloblasts, giant band forms, and giant metamyelocytes (picture 26). There is also a lack of synchrony between the nuclear and cytoplasmic maturation (picture 27), resulting in cells that have a cytoplasm that is more mature-appearing than their nucleus. (See "Treatment of vitamin B12 and folate deficiencies".)

Leukemia — The diagnosis of acute or chronic leukemia is confirmed and classified via examination of the bone marrow. There is usually partial or nearly total replacement of the cellular component of the marrow by immature or undifferentiated cells that, according to the World Health Organization (WHO) classification system, should usually exceed 20 percent. (See "Clinical manifestations, pathologic features, and diagnosis of acute myeloid leukemia", section on 'Diagnosis'.)

Morphologic, immunophenotypic (or cytochemical), cytogenetic, and molecular studies must be performed in every case of suspected leukemia. Information from these studies is important for the correct diagnosis and classification of the leukemia, as it informs the selection of treatment and determination of prognosis.

Acute lymphoblastic leukemia — In the WHO classification system for hematologic malignancies, the lymphoblastic neoplasms (which may present as leukemia and/or lymphoma) are divided into two general categories based upon lineage (see "Classification of hematopoietic neoplasms") [24,25]:

●Precursor B cell lymphoblastic leukemia/lymphoma, also called precursor B cell acute lymphoblastic leukemia (precursor B cell ALL) (see "Clinical manifestations, pathologic features, and diagnosis of B cell acute lymphoblastic leukemia/lymphoma")

●Precursor T cell lymphoblastic leukemia/lymphoma (precursor T-LBL), also called precursor T cell acute lymphoblastic leukemia (precursor T cell ALL) (see "Clinical manifestations, pathologic features, and diagnosis of precursor T cell acute lymphoblastic leukemia/lymphoma")

These two entities are morphologically indistinguishable. On peripheral blood smears, lymphoblasts vary from small cells with scant cytoplasm, condensed nuclear chromatin, and indistinct nucleoli to larger cells with moderate amounts of cytoplasm, dispersed chromatin, and multiple nucleoli (picture 28). A few azurophilic cytoplasmic granules may be present. Auer rods are absent.

In tissue sections, the tumor cells are small to medium-sized, with scant cytoplasm, round, oval, or convoluted nuclei, fine chromatin, and indistinct or small nucleoli (picture 29 and picture 30). Occasional cases have larger cells.

Precursor B cell LBL/ALL is differentiated from precursor T cell LBL/ALL by immunophenotypic analysis, which demonstrates B cell antigens and the absence of T cell antigens. In addition, precursor B and T cell LBL/ALL are differentiated from acute myeloid leukemia by their positivity for TdT and lack of staining for myeloperoxidase.

The former French-American-British (FAB) classifications of ALL as L1 and L2 categories did not distinguish precursor B ALL from precursor T cell ALL. The former FAB L3 category is currently described as Burkitt lymphoma/leukemia in the WHO classification.

Acute myeloid leukemia — Acute myeloid leukemia (AML) is diagnosed by bone marrow biopsy using morphologic, cytochemical, immunophenotypic, and cytogenetic/molecular analysis. The blast forms must be identified as cells of the myeloid (as distinct from the lymphoid) lineage. Blast forms must account for at least 20 percent of the total cellularity of the bone marrow biopsy sample; exceptions to this threshold value include leukemias with certain genetic abnormalities or myeloid sarcoma, which are considered diagnostic of AML without regard to the blast count. (See "Clinical manifestations, pathologic features, and diagnosis of acute myeloid leukemia".)

AML is classified using the WHO classification system, which recognizes six main groups (table 2) (see "Acute myeloid leukemia: Classification") [25]:

●AML with recurrent genetic abnormalities

●AML with myelodysplasia-related features

●Therapy-related AML and myelodysplastic syndrome (MDS)

●AML, not otherwise specified

●Myeloid sarcoma

●Myeloid proliferations related to Down syndrome

Blastic plasmacytoid dendritic cell neoplasm is a rare hematologic neoplasm arising from the precursors of plasmacytoid dendritic cells. While it was discussed as a type of myeloid leukemia in the 2008 WHO classification, insight into the ontogeny of the tumor has resulted in its classification as a unique category. (See "Blastic plasmacytoid dendritic cell neoplasm".)

AML, not otherwise specified are subclassified by morphology that is similar to that used in the FAB classification system:

●AML with minimal differentiation (FAB M0) (picture 31) lack differentiating features and do not demonstrate either cytoplasmic granules or Auer rods, although they do express myeloid antigens.

●AML without maturation (FAB M1) (picture 32) are large cells with a high nuclear:cytoplasmic ratio with grayish blue cytoplasm, no granules, and a nucleus containing one to two distinct nucleoli.

●AML with maturation (FAB M2) (picture 33) are slightly more mature than M1 blasts; many of the cells contain granules and occasionally Auer rods can be noted, which are rod-like structures made up of coalesced granules or lysosomal material (picture 34).

●Acute myelomonocytic leukemia (FAB M4) is usually an admixture of myeloblasts, promyelocytes, monoblasts and promonocytes (picture 35).

●Acute monoblastic and monocytic leukemia (FAB M5) has oval and indented nuclei containing opaque cytoplasm and fine granules (picture 36 and picture 37 and picture 38).

●Pure erythroid leukemia (FAB M6) is made up of abnormal erythroblasts with features of nuclear pulverization, gigantism and multinucleated cells, admixed with myeloblasts (picture 39).

●Acute megakaryoblastic leukemia (FAB M7) is made up of abnormal blasts that may resemble those seen in AML with minimal differentiation or AML without maturation. They are differentiated from the others by virtue of either maturation to cells resembling normal megakaryocytes, as in the left panel (picture 40), or by special staining for the products of megakaryocytes, such as von Willebrand factor or platelet type glycoproteins, as in the right panel (picture 40).

Acute promyelocytic leukemia — Acute promyelocytic leukemia (APL; FAB M3 blast cells) (picture 41) is made up of myeloblasts that resemble promyelocytes. Granules may be so pronounced that they almost obscure the nuclear cytoplasmic borders; occasionally, the hypergranular cells contain bundles of Auer rods (picture 42). Another variant of APL includes the microgranular type, in which the granules are not as apparent (picture 43). (See "Clinical manifestations, pathologic features, and diagnosis of acute promyelocytic leukemia in adults".)

Chronic lymphocytic leukemia — The bone marrow smear in patients with chronic lymphocytic leukemia (CLL) and its variant chronic prolymphocytic leukemia is hypercellular with monotonous areas of small round cells containing a thin rim of cytoplasm (picture 2). On higher power the lymphocytes can be clearly distinguished from erythroid precursors (picture 44), with the mature lymphocytes of CLL being small round cells with pyknotic nuclei and scant blue cytoplasm, whereas the most mature normoblasts have a more clumped nuclear chromatin along with a greater amount of cytoplasm which is either bluish-red (polychromatophilic normoblast) or reddish (orthochromatic normoblast). (See "Clinical features and diagnosis of chronic lymphocytic leukemia/small lymphocytic lymphoma".)

CLL and the indolent lymphoma, small lymphocytic lymphoma, are considered by the WHO classification scheme to be the same disease in different clinical phases [26].

Chronic myeloid leukemia — The bone marrow in chronic myeloid leukemia (CML) is most often hypercellular, with a markedly increased M:E ratio due to an absolute increase in cells of the myeloid series. The most abundant cells are usually myelocytes, metamyelocytes, and mature neutrophils, with myeloblasts usually representing <5 percent of all cells of the myeloid series (picture 17). Auer rods are not seen unless the disease has transformed into an acute myeloid leukemia. (See "Clinical manifestations and diagnosis of chronic myeloid leukemia".)

Myelodysplastic syndromes — The myelodysplastic syndromes (MDS) often present clinically in a fashion similar to that of the acute leukemias, with laboratory findings of anemia, thrombocytopenia, and neutropenia. Associated findings on the peripheral smear may include varying degrees of macrocytosis of the circulating red cells, monocytosis, and dysplastic changes in the circulating granulocytes (eg, acquired pseudo-Pelger-Huët changes) (picture 45).

In MDS, bone marrow smears reveal erythroid immaturity with nuclear-cytoplasmic dyssynchrony. In addition, there may be abnormal myeloid maturation with increased immaturity, and mature forms with decreased lobes (Pelger-Huët cells) and abnormal, poorly lobulated micro-megakaryocytes (picture 46).

In MDS, iron staining of the marrow aspirate may also show erythroid precursors with many iron-containing granules, often completely surrounding the nucleus (ring sideroblasts) (picture 47). (See "Clinical manifestations, diagnosis, and classification of myelodysplastic syndromes (MDS)".)

Lymphoma — Involvement of the bone marrow by lymphoma may present with anemia, thrombocytopenia, and/or neutropenia. Cytopenias may be due to replacement of normal hematopoietic elements by lymphoma but may also be caused by immune destruction (eg, autoimmune hemolytic anemia, thrombocytopenia, or neutropenia). In some cases, examination of peripheral blood smear will reveal circulating lymphoma cells.

Bone marrow biopsy may reveal patchy involvement by lymphoma or monotonous replacement of normal marrow elements (picture 48); in some cases the demonstration of clonality by flow cytometry or molecular studies is required to distinguish marrow involvement by lymphoma from resident lymphoid cells or reactive lymphoid nodules. Lymphoma involving the bone marrow typically resembles the histology of nodal disease; occasionally, primary lymphoma of bone is seen.

Bone marrow biopsy is recommended for staging of most types of non-Hodgkin lymphoma and some cases of Hodgkin lymphoma. (See "Pretreatment evaluation, staging, and treatment stratification of classic Hodgkin lymphoma", section on 'Other procedures' and "Pretreatment evaluation and staging of non-Hodgkin lymphomas", section on 'Bone marrow examination'.)  

Multiple myeloma — Multiple myeloma typically presents in the bone marrow with sheets of abnormal plasma cells, which may vary from immature plasmablasts and proplasmacytes to more mature plasma cells with an eccentrically-placed nucleus and a "clock-face" or "cartwheel" pattern of nuclear chromatin without nucleoli (picture 49). Occasionally the cytoplasm of myeloma cells may contain condensed or crystallized cytoplasmic immunoglobulin resulting in "Mott cells," "Russell bodies," "flame cells," and "Gaucher-like cells," findings that may be seen in other entities. (See "Multiple myeloma: Clinical features, laboratory manifestations, and diagnosis", section on 'Morphology and immunophenotype'.)

However, multiple myeloma may present with spotty areas of marrow involvement, such that aspirate smears from one marrow site may be normal, while others taken from the same or distant sites may be infiltrated with malignant cells. Diagnosis must take into account both pathologic and clinical features (table 3).  

Waldenström macroglobulinemia — Waldenström macroglobulinemia (WM) is suspected in patients presenting with an IgM monoclonal spike on serum protein electrophoresis, often with signs and symptoms of hyperviscosity and the presence of anemia. The marrow is infiltrated by cells which have been termed plasmacytic lymphocytes ("plymphocytes") or lymphoplasmacytic cells, resembling a cross between a mature plasma cell and a small lymphocyte (picture 50). The abnormal cell in WM is a member of the lymphocytic series, but has more cytoplasm than a normal small lymphocyte, giving the cell a slightly eccentric nucleus. Accumulation of cytoplasmic immunoglobulin in some cells results in inclusions known as Russell bodies (cytoplasmic) or Dutcher bodies (pseudonuclear) depending on their intracellular location (picture 51 and picture 52). (See "Epidemiology, pathogenesis, clinical manifestations, and diagnosis of Waldenström macroglobulinemia" and "Clinical manifestations, pathologic features, and diagnosis of lymphoplasmacytic lymphoma", section on 'Bone marrow'.)

Polycythemia vera — Polycythemia vera is usually discovered incidentally when an elevated hemoglobin or hematocrit is noted on a complete blood count. Other findings may include hypochromic, microcytic red blood cells; leukocytosis and/or thrombocytosis; splenomegaly; disease-related symptoms (eg, headache, dizziness, visual disturbances, pruritus, early satiety); or complications (eg, thrombosis, bleeding). A leukoerythroblastic appearance (eg, teardrop-shaped red blood cells, poikilocytosis, and circulating nucleated red cells) may be seen if postpolycythemic myelofibrosis develops (picture 53), and circulating myeloblasts may be seen with leukemic transformation. (See "Clinical manifestations and diagnosis of polycythemia vera", section on 'Clinical presentation'.)

Bone marrow biopsy classically shows prominent erythroid, granulocytic, and megakaryocytic proliferation (picture 54), but findings may evolve from a polycythemic phase to postpolycythemic myelofibrosis ("spent" phase) or leukemic transformation.

Primary myelofibrosis — Primary (idiopathic) myelofibrosis is suspected in patients presenting with an enlarged spleen, varying degrees of anemia, teardrop-shaped red cells (picture 55) and a leukoerythroblastic blood smear (picture 53). (See "Evaluation of the peripheral blood smear", section on 'Leukoerythroblastic smear'.)

Bone marrow aspiration in this disorder often results in a "dry tap", due to the presence of extensive infiltration of the marrow with mature and immature collagen and fibrous tissue, which is usually only demonstrated on bone marrow biopsy (picture 56 and picture 57). (See "Clinical manifestations and diagnosis of primary myelofibrosis".)

Essential thrombocythemia — Essential thrombocythemia, also called primary or idiopathic thrombocytosis, is suspected in a patient with a markedly elevated platelet count (picture 58 and picture 59), and varying degrees of bleeding and/or thrombosis. The bone marrow is most often normocellular, in contrast to polycythemia vera, in which the bone marrow is hypercellular. There are no bone marrow findings pathognomonic for this disorder, although megakaryocytic hyperplasia with or without clusters of mature or immature megakaryocytes is a common finding (picture 54). (See "Clinical manifestations, pathogenesis, and diagnosis of essential thrombocythemia".)

Systemic infection — Systemic infection is often suspected in patients with unexplained fever, organomegaly, and/or lymphadenopathy. Staining of bone marrow aspirates for infectious bacterial, fungal, or viral agents is often helpful in establishing the diagnosis (picture 60 and picture 61) [27]. (See "Fever of unknown origin in adults: Evaluation and management", section on 'Targeted testing'.)

Iron stores — Bone marrow iron staining (Prussian blue stain) is considered by most clinicians to be the gold standard for determining iron stores. However, this often is not required in individuals for whom review of the clinical history, peripheral blood smear, and serum iron studies is sufficient to establish the diagnosis.

Iron deficiency is characterized by lack of stainable iron in erythroid precursor cells and bone marrow macrophages. In contrast, anemia of chronic disease is associated with iron in macrophages (often abundant) but not in erythroid precursors (picture 62).

As noted above, iron staining is also used to identify abnormal iron deposits in erythroid precursors (eg, ring sideroblasts) in myelodysplastic syndromes. (See 'Myelodysplastic syndromes' above.)

SUMMARY

●Purpose – Bone marrow (BM) aspiration is generally used for diagnosis and/or staging of hematologic disorders and certain non-hematologic disorders.

●Procedure – BM aspiration is often performed together with a BM needle core biopsy. BM examination is an ambulatory procedure with low morbidity that is readily performed using local anesthesia, as discussed separately. (See "Bone marrow aspiration and biopsy: Indications and technique".)

●Analysis

•Microscopy – Most laboratories employ Wright-Giemsa staining of the aspirate specimen to highlight nuclear and cytoplasmic characteristics.

-Low power – Examination using low power enables evaluation of adequacy of the sample (eg, presence of bone marrow spicules) and the ratio of fat to overall cellularity. Low power evaluation is important for detecting cellular monotony, clumps of tumor cells, and storage cells. (See 'Low power examination of the marrow' above.)

The largest normal cell in bone marrow is the megakaryocyte, which is responsible for platelet production. The presence of other large cells is an abnormal finding, and may indicate the presence of disease, such as Hodgkin lymphoma, parvovirus infection, metastatic malignancy, or a storage disease. (See 'Large cells' above.)

-High power – Examination using high power enables estimation of the of the myeloid to erythroid ratio and the maturation sequences of major cellular elements. High power view is important for detecting aberrant maturation (eg, megaloblastic changes), malignant hematopoietic cells, microorganisms, and iron stores. (See 'High power examination of the marrow' above.)

•Special stains – The aspirate specimen may be evaluated using special stains. Examples include testing for clonality (eg, immunoglobulin light chains), reticulin or collagen (eg, silver and trichrome stains), amyloid (eg, Congo red staining), and/or staining for microbial agents. (See 'Staining' above.)

•Other testing – Flow cytometry for immunophenotyping and molecular testing for diagnosis and measurable residual disease (MRD) are often performed using the aspirate specimen.

ACKNOWLEDGMENT — The editors of UpToDate acknowledge the contributions of Stanley L Schrier, MD as Section Editor on this topic, his tenure as the founding Editor-in-Chief for UpToDate in Hematology, and his dedicated and longstanding involvement with the UpToDate program.