Bone marrow aspiration, also called bone marrow sampling, is the removal by suction of the soft, spongy semisolid tissue (marrow) that fills the inside of the long and flat bones. Bone marrow biopsy, or needle core biopsy, is the removal of a small piece (about 0.75 X 0.06 in, or 2 X 0.16 cm) of intact bone marrow. The bone marrow is where blood cells are made.
Examination of the bone marrow may be the next step that follows an abnormal clinical finding, such as an abnormal complete blood count (CBC), and/or an abnormal peripheral blood smear. It may also be performed following an abnormal bone image such as the finding of a lesion on x rays.
A biopsy of bone marrow shows the intact tissue, so that the structure of the fat cells, lymphocytes, plasma cells, fibrous connective tissue cells, and other cells, and their relationships to each other, can be seen. A bone marrow biopsy is used to:
The combination of aspiration and biopsy procedures are commonly used to ensure the availability of the best possible bone marrow specimen. The aspirate is collected at the same time as the bone core biopsy by attaching a syringe to the bone marrow needle and withdrawing the sample before the cutting blades are inserted and the bone core is removed. The aspirate is the sample of choice for studying and classifying the nucleated blood cells of the bone marrow (e.g., determining the ratio of immature white blood cells to red blood cells (M:E ratio). The biopsy is the only sample that shows the blood forming cells in relation to the structural and connective tissue elements (i.e., the microarchitecture) of the bone marrow. It provides the best sample for evaluating the cellularity of the bone marrow (the percentage of blood-forming tissue versus fat).
Bone marrow aspiration and biopsy are performed by a pathologist, hematologist, or oncologist with special training in this procedure. The procedure may be performed on an outpatient basis. In adults, the specimen is usually taken from the posterior superior iliac crest (hip). The sternum (breastbone) may be used for aspiration, but is less desirable because it carries the risk of cardiac puncture. Other sites that are rarely used are the anterior superior iliac crest or a spinal column bone. When the patient is a child, the biopsy site is generally the anterior tibia, the larger of the two bones in the lower leg. A vertebra may also be used.
The skin covering the biopsy site is cleansed with an antiseptic, and the patient may be given a mild sedative. The patient is positioned, and a local anesthetic such as lidocaine is administered first under the skin with a fine needle and then around the bone at the intended puncture site with a somewhat larger gauge needle. When the area is numb, a small incision is made in the skin and the biopsy needle is inserted. Pressure is applied to force the needle through the outer bone, and a decrease in resistance signals entry into the marrow cavity. The needle most often used for bone marrow biopsy is a Jamshidi trephine needle or a Westerman-Jensen trephine needle. A syringe is placed on the top of the needle and 1–2 ml of the bone marrow is aspirated into the syringe. In some instances, the marrow cannot be aspirated because it is fibrosed or packed with neoplastic cells. The syringe is removed and the medical technologist uses this sample to prepare several smears containing small pieces of bone (spicules). Another syringe is fitted onto the needle hub and another sample of 3 ml is removed and transferred to a tube containing EDTA for analysis by flow cytometry, cytogenetic testing, or other special laboratory procedures. Following aspiration, the cutting blades are inserted into the hollow of the needle until they protrude into the marrow. The needle is then forced over the tips of the cutting blades and the needle is rotated as it is withdrawn from the bone. This process captures the core sample inside the needle. A wire probe is inserted at the cutting end and the bone marrow sample is pushed through the hub of the needle onto sterile gauze. The specimen is used to make several preparations on glass slides or coverglasses and is transferred to a fixative solution.
In the laboratory, the aspirate slides are stained with Wright stain or Wright-Giemsa stain. The biopsy material is sectioned onto glass slides and stained with hematoxylin-eosin, Giemsa, and Prussian blue stains. Prussian blue stain is used to evaluate the amount of bone marrow iron, and the other stains are used to contrast cell structures under the microscope. In addition, special stains may be used that aid in the classification of malignant white blood cells.
The physician should be informed of any medication the patient is using and any heart surgery that the patient may have undergone.
Adults require no special preparation for this test. As for infants and children, they need physical and psychological preparation depending on the child's age, previous medical experiences, and level of trust.
Before the test, parents should know that their child will most probably cry, and that restraints may be used. To provide comfort, and help their child through this procedure, parents are commonly asked to be present during the procedure. Crying is a normal infant response to an unfamiliar environment, strangers, restraints, and separation from the parent. Infants cry more for these reasons than because they hurt. An infant will be restrained by hand or with devices because they have not yet developed the physical control, coordination, and ability to follow commands as adults have. The restraints used thus aim to ensure the infant's safety.
Parents should prepare a toddler for bone marrow aspiration directly before the procedure, because toddlers have a very short attention span. Some general guidelines for parents include the following:
Parents should prepare a preschooler for bone marrow aspiration directly before the procedure, so that the child does not worry about it for days in advance. Explanations should be limited to 10 or 15 minutes, because preschoolers also have a limited attention span. Parents should also ensure that the child understands that the procedure is not a punishment. Some general guidelines for parents include the following:
Explanations should be limited to 20 minutes, and repeated if required. School-age children have a good concept of time, allowing for preparation in advance of the procedure. The older the child, the earlier a parent can start preparation. Guidelines for parents include the ones provided for preschoolers as well as the following:
An adolescent is best prepared by being provided with detailed information and reasons for the procedure. Adolescents should be encouraged to make as many decisions as possible. An adolescent may or may not wish a parent to be present during the procedure, and such wishes should be respected, since privacy is important during adolescence. Other guidelines include the following:
After the needle is removed, the biopsy site is covered with a clean, dry pressure bandage. The patient must remain lying down and is observed for bleeding for one hour. The patient's pulse, breathing, blood pressure, and temperature are monitored until they return to normal. The biopsy site should be kept covered and dry for several hours.
The patient should be able to leave the clinic and resume most normal activities immediately. Patients who have received a sedative often feel sleepy for the rest of the day; so driving, cooking, and other activities that require clear thinking and quick reactions should be avoided. Walking or prescribed pain medications usually ease any discomfort felt at the biopsy site, and ice can be used to reduce swelling.
A doctor should be notified if the patient:
A small amount of bleeding and moderate discomfort often occur at the biopsy site. Rarely, reactions to anesthetic agents, infection, and hematoma (blood clot) or hemorrhage (excessive bleeding) may also develop. In rare instances, the heart or a major blood vessel is pierced when marrow is extracted from the sternum during bone marrow biopsy. This can lead to severe hemorrhage.
Healthy adult bone marrow contains yellow fat cells, connective tissue, and red marrow that produces blood. Bone marrow is evaluated for cellularity, megakaryocyte production, M:E ratio, differential (classification of blood forming cells), iron content, lymphoid, bone, and connective tissue cells, and bone and blood vessel abnormalities. The bone marrow of a healthy infant is primarily red (75–100% cellularity), but the distribution of blood forming cells is very different than adult marrow. Consequently, age-related normal values must be used.
Microscopic examination of bone marrow can reveal leukemia, granulomas, myelofibrosis, myeloma, lymphoma, or metastatic cancers, bone marrow infection, and bone disease. Bone marrow evaluation is usually not needed to diagnose anemia, but may be useful in cases that cannot be classified by other means.
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Mark A. Best Monique Laberge, PhD
A physician requests or orders the procedure. The aspirate and biopsy are most often performed in a hospital or clinic by a hematologist or pathologist that has been trained in the procedure. The analysis of the bone marrow is done by a pathologist, and a written report is added to the patients medical record. A histologic technician performs special stains for bone marrow. Clinical laboratory scientists/medical technologists perform smear reviews and analysis of bone marrow cells by flow cytometry. Cytogenetic technologists may perform chromosomal analysis of bone marrow white blood cells.