What is Bone Specimen - Small?
Also Known As:
Bone Marrow Examination
Bone marrow is the soft and sponge-like tissue found inside the body’s larger bones that produces blood cells. Bone marrow aspiration and biopsy are procedures used to collect and evaluate bone marrow cells and structures.
Bone marrow has a honeycomb or sponge-like structure, consisting of a fibrous network that is filled with liquid. The liquid portion contains blood (hematopoietic) stem cells, blood cells in various stages of maturation, and “raw materials” such as iron, vitamin B12, and folate that are required for cell production.
The primary function of the bone marrow is to produce red blood cells (RBCs), platelets, and white blood cells (WBCs). The number and type of cell being produced at any one time are based on your body’s needs (for example, if you are fighting an infection, or to keep up with blood loss) as well as a normal, continual replacement of old cells.
Red Blood Cells (RBCs)
Red blood cells, also called erythrocytes, transport oxygen throughout the body. RBCs typically makeup about 40-45% of the blood volume and usually survive in circulation for about 120 days. The marrow produces RBCs at a rate that replaces old RBCs that age and degrade or are lost through bleeding, striving to maintain a relatively constant number of RBCs in the blood.
White Blood Cells (WBCs)
There are five different types of white blood cells: lymphocytes, neutrophils, eosinophils, basophils, and monocytes. Each plays a different role in protecting the body from infection.
Platelets, also called thrombocytes, are cytoplasmic fragments of very big cells seen in the bone marrow called megakaryocytes and are essential for normal blood clotting.
In the bone marrow, a stem cell undergoes development and differentiation to become one of these different types of blood cells. Those that differentiate into lymphoid cells subsequently develop into lymphocytes. Other precursors further develop and differentiate into granulocytes (neutrophils, eosinophils, basophils), monocytes, platelets, or red blood cells (erythrocytes).
The cells are released from the bone marrow into circulation when they are fully mature or near full maturity. Thus, the population of cells within bone marrow will typically include cells in various stages of development, from very immature to almost fully mature.
Bone marrow aspiration and/or biopsy as “tests” include both the collection of marrow samples and the evaluation of the cells and structure under the microscope. Bone marrow samples can also be sent as needed for various other tests like flow cytometry immunophenotyping, chromosome analysis, fluorescence in situ hybridization (FISH), molecular testing, or microbiology testing (culture). A specialist who has expertise in the diagnosis of blood-related disorders performs the examination and evaluation of bone marrow samples.
Bone Marrow Aspiration
A bone marrow aspiration collects a sample of the fluid that contains cells so that they can be examined under a microscope and/or evaluated with other tests. A specialist microscopically examines slides of stained smears of the fluid from an aspiration. The cells are evaluated according to number, type, maturity, appearance, etc., and compared to those in the blood using results from a complete blood count (CBC) and blood smear. This examination 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
Bone Marrow Biopsy
A biopsy collects a cylindrical core sample that preserves the marrow’s structure. The biopsy sample is evaluated by a specialist to determine:
- Cellularity—the volume of cells is compared to the volume of other components of the bone marrow, such as fat (and whether cellularity is normal for age, increased, or decreased)
- Whether the different cell lineages (myeloid, erythroid, and megakaryocytic) are present in adequate numbers
- If there are any abnormal infiltrates in the marrow (cancer, infection) as well as any changes to the bone marrow stroma (fibrosis, for example) or bone itself (osteoporosis)
Depending on what condition(s) a healthcare practitioner suspects or is investigating, a number of other tests may be performed on the marrow sample. A few examples include:
- In the case of leukemia, tests to determine the type of leukemia may be done. These include the determination of antigenic markers (for example, immunophenotyping by flow cytometry) to provide information on the type of leukemia present, including prognostic or therapeutic markers.
- Special stains may also be used to evaluate iron storage in the marrow and to determine whether an abnormal erythroid (RBC) precursor with iron particles surrounding its nucleus (so-called ring sideroblasts) is present.
- Chromosome analysis and/or FISH analysis may be ordered to detect chromosomal abnormalities in the case of leukemia, myelodysplasia, lymphoma, or myeloma.
- Molecular tests may be performed on a sample of bone marrow to help establish a diagnosis. Examples include:
- T-cell receptor gene rearrangement
- B-cell immunoglobulin gene rearrangement
- JAK2 mutation
- Bone marrow may be cultured to look for viral, bacterial, or fungal infections that can cause a “fever of unknown origin.” Certain bacteria and fungi can also be detected by special stains.
How is the sample collected for testing?
The bone marrow aspiration and/or biopsy procedure is performed by a doctor or other trained specialist. Both types of samples may be collected from the hip bone (iliac crest). Sometimes, a bilateral procedure is performed, in which bone marrow is collected from both the left and right hips.
The most common collection site is the iliac crest (top ridge) of the back of the hip bone (although sometimes the front of the hip bone is sampled). Before the procedure, some patients may need to receive a transfusion, if their blood counts are very low, to prevent excessive bleeding. Most adults tolerate the procedure very well, but some may be given a mild sedative if they are very anxious. Children are frequently put under anesthesia. The patient is then asked to lie down on his or her stomach or side or back for the collection, and the person’s lower body is draped with cloths so that only the area surrounding the site is exposed.
The site is cleaned with an antiseptic and injected with a local anesthetic. When the site has numbed, the health practitioner inserts a needle through the skin and into the bone. For aspiration, a syringe is attached to the needle to collect a small amount of marrow. For a bone marrow biopsy, a special needle is used that allows the collection of a solid core (a cylindrical sample) of marrow.
Even though the patient’s skin has been numbed, the patient may feel brief but uncomfortable pulling and/or pushing pressure sensations during these procedures. After the needle has been withdrawn, a sterile bandage is placed over the site, and pressure is applied. The entire procedure typically lasts only minutes. The patient is then asked to keep the collection site dry and covered for about 48 hours.
How is it used?
Bone marrow aspiration and biopsy are procedures used to evaluate the blood cells within the bone marrow, as well as their structure. They are performed in conjunction with a complete blood count (CBC) and blood smear and sometimes additional testing on the bone marrow to provide information about the health of the bone marrow and its capability for blood cell production, including red blood cells (RBCs), white blood cells (WBCs), and platelets.
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 cell counts, including too few or too many white blood cells (leukopenia or leukocytosis), too few or too many red blood cells (anemia or polycythemia), or too few or too many 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 and subclassify 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 or solid tumors, 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)
- Diagnose a disorder associated with iron storage that may cause stored iron to diminish
If a person is being treated for 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.