Bone marrow is the soft, sponge-like substance that creates blood cells inside the body’s major bones. The techniques of bone marrow aspiration and biopsy are used to collect and assess the cells and structure of the bone marrow.
Bone marrow is made up of a fibrous network that is filled with fluids and has a honeycomb or sponge-like shape. The liquid component contains blood (hematopoietic) stem cells, blood cells in various stages of maturity, and “raw materials” for cell formation such as iron, vitamin B12, and folate.
The production of red blood cells (RBCs), platelets, and white blood cells is the fundamental function of the bone marrow (WBCs). The amount and kind of cells produced at any given time are determined by your body’s needs (for example, if you’re fighting an illness or trying to keep up with blood loss), as well as a regular, ongoing replacement of old cells.
RBCs (Red Blood Cells)
Erythrocytes, or red blood cells, deliver oxygen throughout the body. RBCs makeup roughly 40-45 percent of blood volume and have a lifespan of about 120 days in circulation. The marrow strives to maintain a generally constant amount of RBCs in the blood by producing RBCs at a rate that replaces old RBCs that age and degrade or are lost through bleeding.
White Blood Cells (WBCs)
White blood cells are divided into five categories: lymphocytes, neutrophils, eosinophils, basophils, and monocytes. Each one protects the body from infection in a distinct way.
Platelets, also known as thrombocytes, are cytoplasmic remnants of megakaryocytes, which are very large cells found in the bone marrow and are required for optimal blood clotting.
A stem cell develops and differentiates in the bone marrow to become one of these different types of blood cells. Lymphocytes develop from lymphoid cells that have differentiated into lymphoid cells. Other precursors go on to become granulocytes (neutrophils, eosinophils, and basophils), monocytes, platelets, and red blood cells (erythrocytes).
When the cells are fully mature or near full maturity, they are released from the bone marrow into circulation. As an outcome, the population of cells in bone marrow typically includes cells at various stages of development, ranging from immature to nearly fully mature.
Aspiration and/or biopsy of the bone marrow are “tests” that include taking marrow samples and examining the cells and structure under a microscope. Bone marrow samples can also be submitted for other tests such as flow cytometry immunophenotyping, chromosomal analysis, fluorescence in situ hybridization (FISH), molecular testing, and microbial testing if needed (culture). The inspection and evaluation of bone marrow samples are performed by a professional with experience in the identification of blood-related illnesses.
Bone Marrow Aspiration
A bone marrow aspiration is a procedure that captures a sample of the fluid that contains cells so that they can be inspected under a microscope and/or tested. A specialist examines slides of colored smears of fluid from an aspiration under a microscope. The cells are analyzed for quantity, kind, maturity, appearance, and other factors before being compared to those found in the blood via a complete blood count (CBC) and blood smear. For example, this examination determines:
The M/E ratio (myeloid/erythroid ratio) is a measurement of how many myeloid cells are in a given number of erythroid cells. The number of myeloid cells (WBC precursors) is compared to the number of erythroid cells in this computation (RBC precursors).
Differential—determines if cells in each lineage (WBC, RBC, platelet-producing cells) have completed their maturation in an orderly and complete manner, as well as whether they are present in a normal proportion to one another. Any aberrant cells, such as leukemic or tumor cells, are present.
Bone Marrow Biopsy
A biopsy takes a cylindrical core sample of the marrow that preserves its structure. A professional examine the biopsy sample to determine:
- Cellularity—the volume of cells in the bone marrow is compared to the volume of other bone marrow components like fat (and whether cellularity is normal for age, increased, or decreased).
- If the various cell lineages (myeloid, erythroid, and megakaryocytic) are present in sufficient numbers.
- If there are any aberrant infiltrates in the marrow (cancer, infection), as well as any changes to the stroma of the bone marrow (fibrosis, for example) or the bone itself, consult your doctor (osteoporosis).
A number of different tests on the marrow sample may be conducted depending on what condition(s) a healthcare practitioner suspects or are researching. Here are a few examples:
- Tests to determine the kind of leukemia may be performed in the case of leukemia. Antigenic indicators (for example, immunophenotyping by flow cytometry) can be determined to provide information on the type of leukemia present, as well as prognostic and therapeutic markers.
- Special stains can also be used to assess iron accumulation in the marrow and to see if an aberrant erythroid (RBC) precursor with iron particles surrounding its nucleus (also known as ring sideroblasts) is present.
- In the case of leukemia, myelodysplasia, lymphoma, or myeloma, chromosome analysis and/or FISH study may be conducted to discover chromosomal abnormalities.
A sample of bone marrow may be subjected to molecular tests to aid in the diagnosis. Here are several examples:
- T-cell receptor gene rearrangement
- B-cell immunoglobulin gene rearrangement
- JAK2 mutation
A doctor or other trained specialist performs the bone marrow aspiration and/or biopsy process. The hip bone can be used to gather both sorts of samples (iliac crest). A bilateral operation, in which bone marrow is taken from both the left and right hips, is sometimes used.
The iliac crest (top ridge) at the rear of the hip bone is the most typical collection site (although sometimes the front of the hip bone is sampled). Some individuals may require a transfusion prior to the procedure if their blood counts are extremely low. This is to prevent excessive bleeding. Most adults endure the treatment well, however, if they are extremely nervous, they may be given a small sedative. Anesthesia is routinely used on children. For the collection, the patient is instructed to lie down on his or her stomach, side, or back, and the lower body is wrapped with cloths so that only the region surrounding the spot is exposed.
A local anesthetic is given after the region is cleansed with an antiseptic. A needle is inserted through the skin and into the bone once the spot has been numbed. A syringe is linked to the needle during an aspiration to extract a little amount of marrow. A specific needle is used to collect a solid core (a cylindrical sample) of marrow during a bone marrow biopsy.
Despite the numbing of the patient’s skin, the patient may experience brief yet unpleasant tugging and/or pushing pressure sensations during these treatments. After the needle has been removed, the wound is covered with a sterile bandage, and pressure is given. The entire treatment usually just takes a few minutes. After that, the patient must keep the collecting site dry and covered for at least 48 hours.