What Is a Bone Marrow Biopsy?

Blood tests can tell a doctor a great deal — but sometimes the numbers keep raising a question they cannot answer on their own. When that happens, the next step is often to look where blood is actually made: inside the bone marrow. A bone marrow biopsy is a test in which a small sample of marrow — the soft tissue in the centre of certain bones where blood cells are produced — is taken and examined in a laboratory. It sounds daunting, and most people who are offered one say so. In practice it is a short, carefully numbed procedure, and it gives information no blood test can match.

The video at the top of this page, titled simply "Bone Marrow Biopsy", shows the procedure itself and runs for just under ten minutes. If you are waiting for this test, watching it beforehand — and reading what follows — can take much of the unknown out of the day.

Why doctors look at the marrow itself

Marrow is the factory, and a blood count is only the finished product rolling off the line. If production is too low, too high, or producing cells that look abnormal under the microscope, examining the factory floor is how specialists find out why. A marrow sample can show whether blood cells are being made in normal numbers and maturing properly, whether the marrow has been replaced or crowded by something that does not belong there, and how conditions already diagnosed are behaving over time.

That is why this test appears in the work-up of unexplained anaemia, persistently abnormal blood counts, and blood and marrow disorders — including the group of cancers discussed in our cancer hub and, more specifically, in our guide to leukemia. It is a close relative of the tissue sampling explained in our general article on what a biopsy is and how results are read, with one difference: marrow is not a lump being sampled, but a living tissue whose cells can be counted, sorted and studied in several different ways from a single visit. And if treatment later involves replacing marrow altogether, our article on bone marrow transplant covers that very different procedure — a biopsy only takes a sample; nothing is transplanted.

Arriving, and getting comfortable

You do not usually need to fast or prepare in any complicated way, but follow whatever instructions your own team sends, and tell them beforehand about any medicines you take — especially anything that thins the blood — and about any allergies. The sample is most often taken from the back of the pelvic bone, near the hip, because marrow is plentiful there and close to the surface. Occasionally another site is chosen, and your team will explain if so.

You will normally lie on your side or on your front on an examination couch, with the skin over the site cleaned and covered with a sterile drape. The area is then numbed with local anaesthetic. That injection stings briefly as it goes in — most people describe it as the sharpest part of the whole appointment — and then the surface goes dull. You stay awake throughout; this is not a general-anaesthetic procedure for most adults.

A shorter companion video on this site, "What to expect when you have a bone marrow test", walks through the same visit in just under two minutes, and its description makes a useful point: the aspiration is usually done first. That is the order you will experience, too.

The two samples, and what each moment feels like

Two related samples are commonly taken through the same numbed spot. The first is the aspiration: a hollow needle is passed through the bone into the marrow, and a small amount of liquid marrow is drawn into a syringe. This takes only seconds, but it is the moment people remember — a strong pulling or aching sensation deep in the bone, sometimes felt down the leg, that passes as soon as the drawing stops. It cannot be fully numbed away, because the inside of the bone cannot be reached by the surface anaesthetic, but it is brief.

The second sample is the biopsy itself — a tiny core of bone and marrow, taken with a slightly wider needle using a gentle twisting motion. You may feel pressure and movement rather than pain. Both samples together usually take only a few minutes once the skin is numb, even though the appointment around them is longer. Afterwards a dressing is applied and you will be asked to lie still for a short while, with the team checking the site before you go home.

It is worth being honest here: this is not a painless test, and anyone who promises you that is not helping. But the uncomfortable moments are measured in seconds, the team doing it performs it routinely, and you can speak up at any point — they would rather pause and add more local anaesthetic than have you endure in silence.

Afterwards: the site, the wait, and the report

The site is often sore and may bruise over the following days, rather like a deep knock. Keep the dressing dry as instructed, take things a little gently at first, and follow the aftercare leaflet your team gives you — including their advice on who to contact if the site becomes increasingly painful, red, or starts to bleed or ooze. Most people are back to normal desk-type activities quickly, but your own team's guidance comes first.

Results take longer than the test itself, because the samples are worked on in stages. The liquid aspirate is spread on slides, stained, and examined cell by cell under the microscope. The solid core is processed and sliced thinly so the laboratory can judge the overall structure of the marrow — how cellular it is, and in what proportions its different cell lines are present. Further tests can be run on the same samples when needed. Your specialist then puts the laboratory report together with your blood results and history; the marrow findings are powerful, but they are one part of the picture, not the whole of it. If low red-cell production is part of your story, our article on anaemia explains the background the marrow test is helping to investigate.

Frequently Asked Questions

Does a bone marrow biopsy hurt?

The local anaesthetic injection stings briefly, and drawing the liquid sample (the aspiration) causes a strong pulling ache that lasts only seconds. The biopsy core is usually felt as pressure. The site is often sore and bruised for a few days afterwards. Tell the team if you are uncomfortable — they can pause and add more anaesthetic.

What is the difference between aspiration and biopsy?

The aspiration draws out liquid marrow, whose individual cells can be spread on slides and studied in detail. The biopsy takes a tiny solid core of bone and marrow, which shows the overall structure. They are usually done together, through the same numbed site, because they answer complementary questions.

How should I prepare?

Preparation is usually simple, but follow your own team's instructions. Tell them in advance about medicines you take — particularly blood-thinning medicines — and about any allergies, and arrange your day so you can rest the site afterwards.

How long do results take?

Longer than the test itself: the samples must be stained, sectioned and examined, and further laboratory tests may be run on them. Your specialist will tell you when to expect the report and will explain it alongside your blood results.

References & further reading

• MedlinePlus — Bone marrow biopsy: https://medlineplus.gov/ency/article/003934.htm
• Johns Hopkins Medicine — Bone Marrow Biopsy: https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/bone-marrow-biopsy
• Cleveland Clinic — Bone Marrow Biopsy: https://my.clevelandclinic.org/health/diagnostics/17735-bone-marrow-biopsy
• National Cancer Institute — Bone marrow biopsy (definition): https://www.cancer.gov/publications/dictionaries/cancer-terms/def/bone-marrow-biopsy

MedicalVideos.com has published trusted medical videos since 2007. The site was founded by Dr. Mohamed Ibrahim, MD, PhD — physician-scientist.

Educational only — this article is general information about bone marrow biopsy, not medical advice and not a diagnosis. Whether this test is right for you, and how to prepare for it, are matters for your own clinician and haematology team, who know your history.