Bone Marrow

Bone marrow aspiration and biopsy are procedures used to evaluate the blood cells within the bone marrow, as well as its structure. They are performed in conjunction with a complete blood count (CBC) and blood smear to provide information about the health of the bone marrow and capability for blood cell production, including red blood cells (RBCs), white blood cells (WBCs), and platelets.

These are not routine tests, and the majority of people will never have them done. However, they are useful in helping to detect, diagnose, monitor and/or stage a number of diseases and conditions that can affect the bone marrow and blood cell production.

A specialist who has expertise in the diagnosis of blood-related disorders performs the examination and evaluation of bone marrow samples. This process determines, for example:

• The M/E ratio—this is short for myeloid/erythroid ratio. This calculation compares the number of myeloid cells (WBC precursors) to erythroid cells (RBC precursors).
• Differential—determines whether cells in each lineage (WBC, RBC, platelet-producing cells) show orderly and complete maturation, and whether the cells are present in normal proportion to one another.
• Presence of any abnormal cells, such as leukemic or tumor cells.
• Cellularity—the volume of cells is compared to the volume of other components of the bone marrow, such as fat.
• The structure of the bone marrow, including the sponge bone (trabecular bone)

Using the information from the examination, a bone marrow aspiration and/or biopsy may be used to help:

• Determine the cause of unexplained low or high blood cells counts, including too few or too many white blood cells (leukopenia or leukocytosis), red blood cells (anemia or polycythemia) or platelets (thrombocytopenia or thrombocythemia)
• Identify the cause of abnormal or immature blood cells present in the blood, as detected by a CBC or a blood smear
• Diagnose cancer originating in the bone marrow, e.g. leukemia, multiple myeloma
• Diagnose other bone marrow disorders such as myelodysplastic syndrome (MDS)
• Diagnose and stage a variety of other types of cancers, such as lymphoma, breast or lung cancer, that may involve or have spread to the bone marrow
• Diagnose conditions that affect the marrow and its fibrous structure, such as myelofibrosis
• Evaluate for a bone marrow infection if a person has a fever without an apparent cause (fever of unknown origin)
• Determine if an individual has a chromosomal abnormality
• Diagnose a disorder associated with iron storage that may cause stored iron to diminish

If a person is being treated for a non-hematopoietic cancer, a bone marrow aspiration and/or biopsy may be ordered to evaluate the response to treatment to determine whether suppressed marrow function is beginning to return to normal.

In addition to microscopic evaluation of the cells and structure, additional tests may be performed, depending on the purpose for testing:

• Immunophenotyping (immunohistochemistry, flow cytometry)
• Chromosome analysis
• Fluorescence in-situ hybridization (FISH)
• T-cell receptor gene rearrangement
• B-cell immunoglobulin gene rearrangement
• mutationJAK2
• BCR-ABL
• PML-RARA
• Culture—detects the presence of fungi, bacteria, or mycobacteria (that causes tuberculosis), for example

These tests are not routinely ordered. However, they may be ordered when results of other tests, such as a CBC and/or blood smear, are abnormal and a bone marrow examination is warranted.

Bone marrow examination may be ordered when an individual's medical history, physical examination, and signs and symptoms suggest that the presence of a disease affecting the bone marrow.

The tests may be ordered when staging certain cancers such as Hodgkin and Non-Hodgkin lymphomas or when it is suspected that other cancers have spread to the bone marrow.

A bone marrow biopsy and aspiration may also be ordered at intervals when a person is being treated for a cancer other than a blood cancer to evaluate whether marrow function is being suppressed and, if it is, when its function begins to recover.

The laboratory report for these tests may include a description of the cells seen or the appearance of the bone marrow environment. Results from a complete blood count (CBC) and blood smear are usually included. Typically, the specialist provides an interpretation of the findings and any other details that might be important in the diagnosis, staging, or treatment of the disease.

In many cases, this information can confirm or rule out a diagnosis and whether the bone marrow is affected by disease, but it can also point out the need for further investigation. For example, a patient with decreased red blood cells (RBCs) and no increase in reticulocytes may have aplastic anemia with suppressed RBC production in the marrow. An evaluation of the bone marrow may confirm this condition, but it does not necessarily tell the health practitioner whether it is due to a primary bone marrow disorder, radiation, exposure to certain chemicals, cancer, cancer treatment, or an infection.

The health practitioner uses the information from the marrow evaluation and combines it with information from a clinical examination, medical history, blood tests, and a variety of other tests, such as imaging scans and X-rays, to reach a final diagnosis. It can be a straightforward process or it can be a complex diagnostic puzzle. Patients should stay involved in this process by talking to their health care provider before and after a bone marrow biopsy and/or aspiration, asking what the suspicions are, what kind of information is expected from the evaluation, and what follow-up tests might be indicated.

A variety of disorders and conditions may be identified, monitored, and/or staged with this process. A few examples include:

• Leukemia is a cancer of the blood cells. It results in the excessive production of one blood cell, resulting in the presence of large quantities of cells that do not function as normal ones do. When leukemic white blood cells (WBCs) crowd out RBC production in the bone marrow, the patient becomes anemic; when they decrease the number of platelets produced, they leave the patient vulnerable to excessive bruising and bleeding. Leukemia of red blood cell (erythroleukemia) in a similar fashion will crowd out WBC and/or platelet precursors.
• Anemia is a low number of red blood cells and low hemoglobin. The marrow should increase the rate of RBC production whenever the number of RBCs in blood decreases. The increased rate of production continues until there is a sufficient number of RBCs in the blood or until marrow production capacity is reached. If the need exceeds capacity, then the number of RBCs in the blood will decrease and the individual will become increasingly anemic, with symptoms such as pallor, fatigue, and shortness of breath due to decreased oxygen-carrying capacity by the red blood cells. Anemia can also occur if the production of RBC in the marrow is suppressed.
• Vitamin and mineral deficiencies, such as vitamin B12 and folate or iron deficiency, can lead to the production of large or small or abnormally shaped RBCs and result in specific types of anemia. Though these may be diagnosed by a bone marrow exam, they rarely are, and mainly are diagnosed by blood tests.
• Diseases such as aplastic anemia that can affect the marrow's ability to produce an adequate number of each of the different blood cell types and release them into circulation. These diseases may affect the overall number of cells produced, the proportion of cells produced, and/or the function of the cells.
• Some other bone marrow disorders may lead to a deficiency of one or more cell types (e.g., myelodysplastic syndrome) while others result in excess production of a specific type or of a specific clone of a cell—a single cell that reproduces without regulation (e.g., polycythemia vera, essential thrombocythemia).
• Myelofibrosis is a disorder characterized by the overgrowth of the fibrous network found in the marrow, compressing cells and leading to changes in red blood cell shape and changes in the cell counts.

Complications from the bone marrow aspiration and/or biopsy procedure are rare, but occasionally people may have excessive bleeding at the collection site or develop an infection. Individuals should tell their health care provider about any allergies they have and about any medications or supplements they are taking prior to the procedure and should contact their health care provider promptly if they experience persistent or spreading redness or bleeding at the site, a fever, or increasing pain.