A bone marrow biopsy is a medical procedure in which a small sample of bone marrow is taken so that it can be examined under a microscope by a pathologist. The bone marrow is the soft tissue found inside bones, and it is where most of your blood cells are made. By looking at a sample of your bone marrow, doctors can learn whether it is healthy and producing normal blood cells, or if there are signs of disease.
Your doctor may recommend a bone marrow biopsy for several reasons, including:
Unexplained changes in your blood: If blood tests show abnormal levels of red blood cells, white blood cells, or platelets, a bone marrow biopsy can help find the cause.
Suspected blood cancers: Conditions such as leukemia, lymphoma, multiple myeloma, or myelodysplastic syndromes often involve the bone marrow.
Other cancers: Some cancers from other parts of the body can spread to the bone marrow.
Nutritional deficiencies or systemic diseases: Low levels of nutrients such as iron or vitamin B12, chronic infections, or kidney disease can affect the bone marrow.
Monitoring disease or treatment: A biopsy may be done to see how well a treatment is working or to check if a disease has returned.
The biopsy is usually done from the hip bone, most often the posterior iliac crest, which is the large bone at the back of your pelvis. After numbing the area with local anesthetic, the doctor uses a special needle to collect bone marrow. The procedure usually takes only a few minutes. You may feel pressure or brief discomfort when the marrow is withdrawn. Two types of samples may be taken:
A bone marrow aspirate is a procedure where a thin, hollow needle is used to remove a small amount of liquid bone marrow. The sample is spread onto glass slides so that individual cells can be examined under the microscope. This allows the pathologist to study the size, shape, and maturity of the blood cells in great detail. They can also count the number of different types of cells present.
Because the aspirate shows the cells as they appear individually, it is very useful for spotting abnormal shapes, sizes, or proportions of cells. However, an aspirate does not show how the cells are arranged within the bone marrow, since the sample is spread out on a slide. In addition, some diseases cause scarring (fibrosis) in the bone marrow, which can make it difficult to collect enough liquid material for the aspirate. In these cases, a core (trephine) biopsy is often required to provide additional information.
A core needle biopsy, sometimes also called a trephine biopsy, is another way of sampling the bone marrow. Like an aspirate, it uses a special needle, but instead of removing liquid marrow, it removes a small, solid piece of bone marrow tissue. This type of sample allows the pathologist to see how the cells are organized and whether the overall structure of the marrow looks normal.
A core or trephine biopsy is especially useful when the bone marrow is scarred (a condition called fibrosis), because scarring can make it very difficult to collect enough liquid marrow with an aspirate. By examining the solid tissue, the pathologist can better evaluate cell organization, the presence of fibrosis, and whether there are abnormal clusters of cells.
A bone marrow biopsy can provide a wide range of results, depending on what the pathologist sees under the microscope. Some of the key terms and findings you may see in your report include:
Pathologists use the term cellularity to describe the balance between blood-forming cells and fat in the bone marrow. Normal cellularity changes with age. Younger people usually have more blood cells and less fat, while older people typically have less blood cells and more fat.
Normocellular marrow: This means the number of cells in your bone marrow is normal for your age.
Hypercellular marrow: This means there are more blood-forming cells than expected for your age. A hypercellular marrow can be seen in conditions such as leukemia, myeloproliferative neoplasms, or as a response to infection.
Hypocellular marrow: This means there are fewer blood-forming cells than expected. A hypocellular marrow may be seen in conditions such as aplastic anemia, after chemotherapy, or in some chronic illnesses.
The term trilineage hematopoiesis describes the presence of all three major types of developing blood cells:
Erythroid lineage: Cells that produce red blood cells.
Granulocytic lineage: Cells that produce white blood cells such as neutrophils.
Megakaryocytic lineage: Cells that produce platelets.
Finding normal trilineage hematopoiesis means all three groups of blood cells are present and developing normally. A report may also mention whether one of these lineages is increased, decreased, or shows dysplasia (abnormal development).
Blasts are the most immature blood cells in the bone marrow. Normally, blasts make up less than 5% of all cells in the marrow. An increased number of blasts may be a sign of leukemia or another serious bone marrow disorder.
Dysplasia: Blood cells that look abnormal in size, shape, or maturity. This can be a sign of myelodysplastic syndrome or another bone marrow disorder.
Spread of other cancers: Cancers that begin outside the bone marrow, such as breast or prostate cancer, can spread to the marrow. This is called metastasis.
Lymphoma or plasma cell disorders: These cancers can involve the marrow and may be described in the report.
Fibrosis: Too much scar tissue in the bone marrow can interfere with its ability to make normal blood cells. This is often seen in myeloproliferative neoplasms.
Iron stores: The marrow normally contains iron, which can be highlighted with a special stain. Too little iron may explain anemia, while abnormal forms of iron storage, such as ring sideroblasts, may suggest certain bone marrow diseases.
Why do I need a bone marrow biopsy?
Will both an aspirate and a core biopsy be performed?
What did my bone marrow biopsy show?
Were there enough cells for the pathologist to make a clear diagnosis?
Do I need additional tests, such as flow cytometry or genetic testing, on my bone marrow sample?
How do these results affect my treatment plan or follow-up?