A bone marrow test is used to diagnose blood cancers like leukemia, lymphoma, and multiple myeloma, as well as non-cancerous blood disorders such as aplastic anemia and myelodysplastic syndromes. It can also detect whether cancers from other parts of the body have spread to the bone marrow. Because bone marrow is where all blood cells are produced, examining it directly gives doctors information that a standard blood draw simply can’t provide.
How the Test Works
Bone marrow has both a liquid portion and a solid portion, and doctors typically sample both during the same appointment. The liquid sample, called an aspiration, is drawn out through a thin needle. The solid sample, called a core biopsy, removes a small cylindrical piece of bone tissue along with the marrow inside it. A valid biopsy core needs to be at least 1 centimeter long to give the pathologist enough tissue to work with.
Both samples go to a specialist, usually a hematopathologist, who examines them under a microscope and runs additional tests. They’re looking at several things: the number and types of blood cells being produced, whether those cells are normal in size and shape, whether abnormal or immature cells are present, and whether there are genetic changes inside the cells that point to a specific disease.
Blood Cancers
Bone marrow testing is essential for diagnosing the major blood cancers. In leukemia, the marrow produces large numbers of immature white blood cells (called blasts) that crowd out healthy cells. A bone marrow sample reveals the percentage of blasts present, which is one of the key measurements used to confirm a leukemia diagnosis and determine its subtype. Acute leukemias, for instance, are defined in part by having 20% or more blasts in the marrow.
In multiple myeloma, the test looks for an abnormal accumulation of plasma cells, a type of white blood cell that normally produces antibodies. Healthy marrow contains a small percentage of plasma cells. When that number climbs significantly, it signals myeloma. Lymphoma, which primarily affects the lymph nodes, can also infiltrate the bone marrow. A biopsy helps determine whether that spread has occurred, which directly affects how the disease is staged and treated.
Beyond confirming a diagnosis, bone marrow tests are also used to monitor how well treatment is working. After chemotherapy, for example, a follow-up biopsy can show whether cancer cells have been reduced or eliminated from the marrow.
Aplastic Anemia and Myelodysplastic Syndromes
Not every bone marrow test is about cancer. Two important non-cancerous conditions, aplastic anemia and myelodysplastic syndromes (MDS), are diagnosed primarily through bone marrow examination. In aplastic anemia, the marrow fails to produce enough blood cells. A biopsy shows dramatically reduced cellularity, meaning the marrow is emptier than it should be, replaced largely by fat cells. Blood tests might show low counts across the board (red cells, white cells, and platelets), but only a marrow sample confirms that the factory itself has shut down rather than pointing to another cause.
MDS is a group of conditions where the marrow produces blood cells that are abnormal in shape, size, or maturity. These defective cells don’t function properly and often die before leaving the marrow. Bone marrow testing in MDS reveals these misshapen cells and can identify specific genetic mutations that help classify which type of MDS is present, which matters because some forms carry a higher risk of eventually progressing to leukemia.
Solid Tumor Staging
Bone marrow biopsy isn’t limited to diseases that start in the blood. Certain solid tumors are known to spread (metastasize) to the bone marrow, and detecting that spread changes the stage of the cancer and the treatment plan. Neuroblastoma, a childhood cancer, is one of the most common examples. Standardized guidelines exist specifically for evaluating bone marrow involvement in neuroblastoma patients. Small cell lung cancer, breast cancer, and prostate cancer can also metastasize to the marrow. Bone marrow aspiration and biopsy remain the gold standard for confirming this kind of spread.
Other Conditions
Bone marrow testing helps diagnose a broader range of conditions than most people realize. Iron deficiency anemia that doesn’t respond to treatment sometimes warrants a marrow exam to check iron stores directly. Unexplained fevers can prompt a biopsy to look for infections that have taken hold in the marrow, including certain fungal or parasitic diseases. Storage disorders, where the body accumulates substances it can’t properly break down, also leave visible signs in marrow cells.
Myeloproliferative disorders, conditions where the marrow overproduces one or more types of blood cells, are another category. These include polycythemia vera (too many red blood cells) and essential thrombocythemia (too many platelets). A bone marrow biopsy helps distinguish these from reactive conditions where high cell counts are caused by something else entirely, like chronic infection or inflammation.
What the Procedure Feels Like
The sample is most commonly taken from the back of the hip bone (the posterior iliac crest). You lie on your side or stomach, and the area is numbed with a local anesthetic. Most people feel pressure and a brief, deep aching sensation when the marrow is drawn out, particularly during the aspiration. The entire procedure typically takes 15 to 30 minutes.
Soreness at the site is normal for a few days afterward. Most people can return to regular activities within 24 hours, though you’ll want to keep the bandage dry and avoid strenuous activity for a day or two. Serious complications like infection or significant bleeding are rare. Results usually take several days to a couple of weeks, depending on how many specialized tests the pathologist runs on the sample.
Why a Blood Test Isn’t Enough
A standard blood test (complete blood count) can tell you how many red cells, white cells, and platelets are circulating in your bloodstream, and it can flag numbers that are too high or too low. But it can’t tell you why. Low blood counts could reflect a production problem in the marrow, destruction of cells after they’re made, or cells being trapped in the spleen. A bone marrow test answers that question by looking at the source directly. It shows whether the right cells are being made in the right amounts, whether they’re maturing normally, and whether anything is present that shouldn’t be, from cancer cells to infectious organisms to genetic abnormalities.