Kids Health Info

Bone marrow aspirate

  • A bone marrow test is where a doctor uses a needle to take a sample of marrow from inside the bone. The sample is usually taken from the bones above the buttocks, which is the back of the pelvis. This procedure is usually done under general anaesthetic. It is a very safe procedure in our hospital.

    Why does my child need a bone marrow test?

    Bone marrow is responsible for making the three main types of blood cells: red blood cells that carry oxygen to the body's organs, white blood cells that help fight infection, and platelets that help with blood clotting to stop you from bleeding if you cut yourself or are injured.

    A bone marrow test is needed to see how young blood cells are forming and if the marrow contains abnormal cells. It is an important test to help diagnose and monitor treatment in a number of medical conditions.

    Is there anything I need to do before the test?

    For the general anaesthetic, your child will need to fast (i.e. not have any food or drinks) beforehand.

    If you are coming from home, you will be told what time to come to day surgery and when your child should stop eating and drinking.

    What happens during a bone marrow test?

    You may come in to the theatre area with your child until they are asleep. Your child will be positioned on their side.

    After the anaesthetic is given, a needle is inserted into the back of the pelvis bone (see illustration below) and a sample of marrow is collected.

    Sometimes a thin core of bone called a trephine is also needed. A trephine biopsy usually takes a few minutes longer. Local anaesthetic is also used with a trephine biopsy to reduce any bruise-like discomfort afterwards. 

    Usually the test takes less than half an hour.

    *Occasionally a different site to the pelvis may be used. You will be told if this will be the case for your child.


    Bone Marrow Aspirate


    Does it hurt?

    When under general anaesthetic, your child will not have pain during the procedure. If they are awake, staff do everything they can to minimise discomfort.

    Sometimes after a 'trephine core biopsy', the site can feel like a bruise. Your child may need simple pain relief, such as paracetamol.

    What are the risks?

    Every anaesthetic carries a very small risk of complication, which will be explained to you by the anaesthetic doctor.

    There may be some minor bruising.

    Each year we do about 600 bone marrow procedures at the RCH. Serious reactions (bleeding, infection and needle breakage) have been extremely rare at the RCH.  

    Do I need to do anything special after a bone marrow procedure?

    Most children are able to continue with a normal day's activities after the test.

    If your child is in nappies or there has been any bleeding, they will have a dressing to cover the aspirate site. You should take this off the next day. Often this is easiest done at bath-time.

    If you think your child is uncomfortable, give them paracetamol. 

    Signs of infection may include redness and warmth around the area. If you are worried for any reason, call your child's hospital specialist.

    Results of the test

    The samples collected require processing in the laboratory before they are looked at under a microscope. Usually an aspirate result is available within one to two days and a trephine biopsy will be available within two to three days. Other special tests may take longer. Your child's specialist will give you the results as soon as possible.

    Key points to remember

    • Bone marrow examination is a very important test needed to examine how young blood cells are formed. 
    • It is a very safe procedure.
    • Talk to a nurse or doctor about ways you can help your child with pain if needed.
    • If your child will need ongoing bone marrow tests, talk to your child's doctors or nurses about using a 'comfort plan'.

    More information

    • Always feel free to ask the doctor performing the test any extra questions you have. The doctor will be from the haematology department and is not usually your child's treating specialist.
    • You may also like to speak with your general practitioner about the test.
    • Kids Health Info factsheet:  Reducing children's pain during tests and procedures.


    Produced by the RCH Dept Haematology and Comfort Kids (Procedural Pain Project). First published in September 2007. Updated September 2012.

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This information is intended to support, not replace, discussion with your doctor or healthcare professionals. The authors of these consumer health information handouts have made a considerable effort to ensure the information is accurate, up to date and easy to understand. The Royal Children's Hospital, Melbourne accepts no responsibility for any inaccuracies, information perceived as misleading, or the success of any treatment regimen detailed in these handouts. Information contained in the handouts is updated regularly and therefore you should always check you are referring to the most recent version of the handout. The onus is on you, the user, to ensure that you have downloaded the most up-to-date version of a consumer health information handout.