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Bone Marrow Examination

By David J. Kuter, MD, DPhil

Sometimes a sample of bone marrow must be examined to determine why blood cells are abnormal or why there are too few or too many of a specific kind of blood cell. A doctor can take two different types of bone marrow samples:

  • Bone marrow aspirate: Removes fluid and cells by inserting a needle into the bone marrow and sucking out fluid and cells

  • Bone marrow core biopsy: Removes an intact piece of bone marrow using a coring device (similar to a larger diameter needle)

The bone marrow aspirate shows what cells, normal and abnormal, are present in the bone marrow. The core biopsy shows how full the bone marrow is with cells and where the cells are located within the marrow. Both types of samples are usually taken from the hipbone (iliac crest), although aspirates are rarely taken from the breastbone (sternum). In very young children, bone marrow samples are occasionally taken from one of the bones in the lower leg (tibia).

Taking a Bone Marrow Sample

Bone marrow samples are usually taken from the hipbone (iliac crest). The person may lie on one side, facing away from the doctor, with the knee of the top leg bent. After disinfecting the skin and numbing the area over the bone with a local anesthetic, the doctor inserts a needle into the bone and withdraws the marrow.

When both types of samples are needed, they are taken at the same time, usually with two different needle sticks. After the skin and tissue over the bone are cleaned, sterilized, and numbed with a local anesthetic, the sharp needle of a syringe is inserted into the bone. For a bone marrow aspirate, the doctor pulls back on the plunger of the syringe and draws out a small amount of the soft bone marrow, which can be spread on a slide and examined under a microscope. Special tests, such as cultures for bacteria, fungi, or viruses, chromosomal analysis, and analysis of cell surface proteins (flow cytometry), can be done on the sample.

Although the aspirate often provides enough information for a diagnosis to be made, the process of drawing the marrow into the syringe breaks up the fragile bone marrow. As a result, determining the original arrangement of the cells is difficult.

When the exact anatomic relationships of cells must be determined and the structure of the tissues evaluated, the doctor also does a core biopsy. A small core of intact bone marrow is removed with an internal coring device. This core is preserved and sliced into thin sections that are examined under a microscope.

A bone marrow sampling generally involves a slight jolt of pain, followed by minimal discomfort. The procedure takes a few minutes.

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