Bone Marrow Aspiration Test (Diagnosis of Blood Disorders)

ImmunityQ&AMeongsiljang Veterinary Advisory Board

We’ve put together everything pet owners need to know about bone marrow aspiration tests, including what they are, when they’re necessary, how the procedure is performed, how to interpret the results, and how to care for your pet during recovery.

What is a Bone Marrow Aspiration Test?

A veterinarian calming a puppy while preparing for an examination.

Bone marrow aspiration is a precise diagnostic test that involves extracting a small sample of bone marrow tissue to directly observe the process of blood cell production. Its true importance lies in being the central test for identifying the cause of anemia, thrombocytopenia, or abnormal white blood cell counts when routine blood tests (CBC) fail to reveal the underlying issue. For the most accurate diagnosis, it is ideal to perform both bone marrow aspiration, which extracts liquid marrow, and bone marrow biopsy, which removes a small piece of bone tissue. The procedure is typically carried out under sedation or anesthesia, and it takes a few days to interpret the results. Bone marrow findings must always be interpreted in conjunction with blood test results obtained on the same day or within a close timeframe to ensure an accurate assessment.

When is the Test Recommended?

We recommend a bone marrow examination when unexplained abnormalities persist for more than five days on routine blood tests. According to veterinary clinical pathology and internal medicine textbooks, the following situations are typical indications: - Aplastic (non-regenerative) anemia: When red blood cells are not being produced sufficiently in the bone marrow and the cause remains unclear - Thrombocytopenia: When a decrease in platelet count persists without an identifiable cause - White blood cell abnormalities: When white blood cell counts are excessively high or low without an apparent cause - Suspected lymphoma or leukemia: When abnormal cells (such as blasts) or abnormal proliferation of lymphocytes are observed in the blood - Staging of metastatic cancer: To determine whether cancer cells have spread to the bone marrow

How is the Procedure Performed?

The procedure is typically performed under sedation or general anesthesia. Because it can be painful, it’s rarely done while the pet is awake, though very calm or critically ill patients may undergo it with just local anesthesia and light sedation. The sample is taken from sites where hematopoietic function persists throughout life, such as the pelvic bone (iliac crest), proximal humerus, proximal femur (trochanter), or sternum. A special needle, like a Jamshidi or Illinois needle, is firmly inserted into the bone. After removing the stylet, a syringe containing a small amount of EDTA is attached to aspirate the bone marrow. Aspiration stops once blood-tinged fluid begins to flow, with 0.2 to 1 mL usually being sufficient. The collected sample is spread onto a glass slide for microscopic examination of cell morphology.

A view of reading bone marrow samples under a microscope

Bone Marrow Aspiration vs. Bone Marrow Biopsy

Item	Bone Marrow Aspiration	Bone Marrow Biopsy
Collection Method	Aspirate liquid bone marrow with a syringe	Remove a portion of bone tissue (core biopsy)
Needle Used	Illinois/Rosenthal needle (15–18G)	Jamshidi needle (11–13G)
What Is Assessed	Cell morphology and type (cytology)	Bone marrow architecture, cellularity, presence of fibrosis (histology)
Anesthesia	Sedation or anesthesia (depending on patient status)	Sedation or anesthesia (depending on patient status)
Recommended Situation	Confirming cellular abnormalities	When cells are difficult to obtain, or when fibrosis or hypoplasia needs to be evaluated

The two tests provide different information, so it is ideal to perform them together, and they are often done simultaneously. The veterinarian decides based on the situation.

Important Pre-Test Considerations

Bone marrow aspiration is a relatively safe procedure, and even if a patient has thrombocytopenia, bleeding at the aspiration site can typically be controlled with pressure, so it is not an absolute contraindication. However, for pets with a severe bleeding tendency, it is safer to undergo a pre-procedural assessment to prepare for potential bruising or bleeding. Since sedation or anesthesia is required, a comprehensive health evaluation must be performed beforehand. Additionally, if your pet is taking any regular medications, please inform your veterinarian, as certain drugs can affect bone marrow. Although infection and anesthesia-related complications are rare, careful patient selection and thorough preparation are essential.

Interpreting Results — What Can We Learn?

Bone marrow examination results are interpreted by evaluating both the cellular composition—specifically the myeloid-to-erythroid (M:E) ratio—and the morphology of the cells. These findings must always be correlated with blood test results obtained on the same day. Key assessment points include: - Erythroid series: To identify non-regenerative anemia and erythroid dysplasia (abnormal red blood cell maturation) - Myeloid series: To differentiate myelodysplastic syndrome (MDS) from leukemia - Megakaryocytes: To determine whether thrombocytopenia originates within the bone marrow - Abnormal cells: To detect the presence of lymphoma or metastatic cancer cells (carcinoma or sarcoma) - Iron stores and other factors: To provide additional clues for diagnosing anemia Interpreting the results typically takes a few days, and the process may take longer if special staining or additional tests are required.

Illustration of bone marrow cells as seen under a microscope

Post-Procedure Recovery and Care

After the procedure, it’s common for your pet to experience mild discomfort at the site, temporary limping, or slight bruising, but these symptoms usually resolve quickly. A small bandage will be applied to the area, and we recommend avoiding strenuous exercise for about a day after recovery. Once your pet wakes up from anesthesia, they may move more slowly or show a decreased appetite, but these effects typically wear off within 24 hours. While infection or anesthesia-related complications are rare, please contact us immediately if you notice severe swelling at the site, fever, or if limping and loss of appetite persist for more than a day.

A dog resting comfortably at home after its check-up.

Special Considerations for Cats

Cats often have anemia or blood disorders linked to infectious causes, particularly FeLV and FIV, so FeLV (feline leukemia virus) and FIV (feline immunodeficiency virus) testing is frequently performed alongside bone marrow examination. In cats with severe anemia or critical systemic conditions, anesthesia poses a significant risk; therefore, individualized protocols are essential, such as administering a blood transfusion first, minimizing sedation levels, or utilizing local anesthesia. While the procedure itself carries relatively low risk, appropriate patient selection and thorough pre-procedural assessment are paramount.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Bone marrow aspiration — does it hurt a lot?

The examination is performed while your pet is under sedation or anesthesia, so they won’t feel any pain during the procedure. After recovery, there may be mild discomfort or brief limping at the site, but these symptoms are usually minor and resolve quickly.

When can my pet return to its normal routine after the examination?

Once your pet has fully recovered from anesthesia, they can resume light activity starting the next day. However, it’s best to avoid jumping or strenuous exercise that could strain the examined area for a few days.

How much does the test cost?

Costs vary significantly depending on the clinic and location, as well as whether anesthesia, cytological evaluation, and special staining are included. For an accurate estimate, please consult with your attending veterinarian.

Is anesthesia really necessary?

Since this procedure involves sampling from inside the bone, it can be quite painful, so sedation or anesthesia is typically required. While very calm, stable pets or critically ill patients may sometimes undergo the procedure with only local anesthesia and strong sedation, this approach is not common.

Can treatment begin immediately based on the test results?

Once the underlying cause is identified, we develop a tailored treatment plan. In cases of severe anemia, supportive therapies such as blood transfusions are administered alongside primary treatment. Additional interventions are determined based on the specific underlying condition, such as tumors. Typically, we outline the next steps in treatment while explaining the diagnostic results.