What is a Bone Marrow Biopsy and Why is it Done?

If your doctor has recommended a bone marrow biopsy, it is natural to feel uneasy about a procedure you have not had before. In practice, it is a routine, well-established outpatient procedure performed regularly by haematologists, and it usually takes well under an hour. Understanding what it involves and why it is needed can make the experience considerably less daunting.

Bone marrow is where blood cells are made, so examining it directly gives information that a standard blood test cannot. Doctors order a bone marrow biopsy to investigate unexplained abnormalities on a complete blood count, such as persistently low or high cell counts; to diagnose suspected blood cancers such as leukemia, lymphoma involving the marrow, or myeloma; to determine the exact subtype and genetic features of a blood cancer, which guides treatment choice; to evaluate unexplained anemia, infections, or bleeding when other tests have not found a cause; and to monitor response to treatment or check for remission after therapy.

A bone marrow biopsy has two parts, usually done together. Bone marrow aspiration draws a small amount of liquid marrow using a thin needle, which is examined for cell counts, cell appearance, and sometimes sent for additional tests such as genetic analysis. Bone marrow biopsy (core biopsy) removes a small cylindrical piece of solid marrow tissue, which shows the overall marrow structure and cellularity that a fluid sample alone cannot capture.

The sample is most commonly taken from the back of the pelvic bone (the posterior iliac crest), an area with accessible marrow and lower risk to surrounding structures. You lie on your side or stomach, the skin is cleaned and numbed with local anesthetic, and the doctor inserts a specialized needle through the bone to collect the sample. The procedure itself typically takes about 10 to 20 minutes.

The local anesthetic injection causes a brief sting, similar to a dental injection. Once the area is numb, most people feel pressure rather than sharp pain during the procedure, though a brief, sharp sensation can occur for a few seconds during the aspiration step, when the marrow fluid is drawn out. Some clinics offer mild sedation for patients who are especially anxious, though it is not always necessary. Mild soreness at the site for a day or two afterward is common and usually manageable with simple pain relief.

Preparation is generally straightforward: you can typically eat and drink normally beforehand unless sedation is planned, and you should tell your doctor about any blood-thinning medication you take, as this may need to be paused. Wearing loose, comfortable clothing helps with access to the biopsy site.

After the procedure, a bandage is placed over the site, and you are usually advised to keep it dry for about 24 hours and to avoid strenuous activity for a day. Most people can resume normal activities the next day. Results, particularly detailed genetic or molecular testing, can take anywhere from a few days to a couple of weeks depending on which tests are ordered.