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Diagnostic Laboratories Bone Marrow Aspirates

Bone Marrow Sampling

Bone marrow is the spongy tissue located inside the bones that produces red blood cells, white blood cells, and platelets.
There are two types of bone marrow sampling:

  • Bone Marrow Aspiration (cytology): Involves collecting a small amount of liquid bone marrow with a bone marrow needle with a stylet. The liquid marrow is then examined under a microscope to assess the types of cells, their morphology, and proportions
  • Bone Marrow Core Biopsy (histopathology): Involves removing a small, solid core of bone marrow tissue. This sample provides more detailed information about the architecture and cellularity of the bone marrow.

A variety of needles are available, which can be reusable (e.g. Rosenthal needle), or disposable (e.g. Illinois sternal needle, Jamshidi needle which can be used to obtain both aspirates and core samples)
Bone marrow sampling should be paired with haematological evaluation of a blood sample taken at or near the same time (within 24hrs). Reviewing haematology collected at the same time provides the most complete picture of what is happening in the marrow at the time of collection.


  • Persistent or unexplained abnormalities in peripheral blood, such as non-regenerative anaemia, or persistent poorly regenerative anaemia, persistent neutropenia bicytopenia, pancytopenia, erythrocytosis
  • Abnormal cells in circulation
  • Investigations for neoplasia (e.g., unexplained hypercalcaemia or monoclonal gammopathy)
  • Staging of neoplasia
  • Investigations for infectious diseases

While these are the most common reasons for examining bone marrow, additional information can sometimes be gained on iron stores, red cell regeneration in horses, and FeLV status in cats. There are often other methods of investigating these issues without resorting to bone marrow; please contact us if you have any questions.

Samples Needed

Samples Needed

  • Venous blood: Collect an EDTA sample and a blood smear on the day of bone marrow sampling. The cost of haematology is included in the cytology price.
  • Aspirate: Ideally, collect directly into an anticoagulant tube to prevent clotting and prepare fresh smears by gently spreading the sample and rapidly air-drying (a hairdryer can be a helpful tool, by placing the back of the slide on the nozzle of a hairdryer on high setting).
    Alternatively, gently expel the marrow onto several vertically positioned slides; the particles will adhere to the slide while the blood flows downward. A squash preparation is then made with the remaining marrow particles on this slide, with a second slide placed over the first slide, without applying excessive pressure; quickly air-dry. The spreader slides can be valuable slides also.
    The material from the syringe can also be placed into a Petri or other similar dish. Marrow particles can then be visualised (often appear granular) and then placed onto a slide directly with a pipette, and then spread and air-dried as above.
    Any excess marrow sample in an EDTA tube can also be submitted alongside the slides.
  • Core Biopsy: Marrow core biopsy should be collected after aspiration, to prevent haemodilution of the aspirated sample. Place the sample into formalin. Optionally, roll the sample on a glass slide before placing it in formalin for cytological evaluation. Do take care with packaging if both core and aspirates are obtained (see “Formalin fumes affecting cytology staining” in Common Problems below) 

The three methods of examination are complementary and individually irreplaceable.

Sampling Sites

Sampling Sites

This is often a matter of personal preference. In our hospital the proximal humerus in both dogs and cats is typically used. Other sites may include the proximal femur, iliac crest (medium to large dogs), or sternum (large dogs), while the costochondral junction (more commonly used in dogs but may be used in cats if needed) is also chosen by some clinicians for aspirate samples. Biopsies may be taken from specific sites if specific lesions are identified using diagnostic imaging.

Common Problems

Common Problems

  • No EDTA blood sample +/- blood smear submitted.
  • Only the EDTA marrow aspirate is submitted (no fresh smears)—morphological degeneration is rapid, especially in hot weather. Post-mortem samples must be taken immediately.
  • Thick marrow smears or unsmeared material can result in samples that are too dense to analyse individual cells.
  • Poor cell preservation due to incomplete drying before placing slides in a case.
  • Formalin fumes affecting cytology staining—always keep cytology aspirates away from the formalin container. Separate plastic bags are the minimum precaution.
  • Absence of marrow spicules on cytology slides, precluding/limiting cytological interpretation (dry tap). Unsuccessful marrow aspiration attempts may be due to technique or may be a result of myelofibrosis or myelopthesis.
  • Core biopsy that is too small or consists solely of cortical bone—white, dense samples are less likely to yield useful information. In some cases, attempts from multiple sites may be necessary.

Our medics and clinical pathologists are available to answer any questions you may have regarding the bone marrow sampling procedure.

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