Indications:
Hematopoiesis is the production of white blood cells, red blood cells, and platelets. Hematopoiesis occurs almost predominantly in the bone marrow. Examination of peripheral blood most often estimates bone marrow activity and this estimate can be reflected in a routine CBC. Occasionally, marrow dysfunction may be suspected from an abnormal CBC and in such circumstance bone marrow evaluation may be necessary.
Bone marrow evaluation is indicated if the following abnormalities are identified on a CBC:
1. Low peripheral blood cell counts are present:
a.unexplained non-regenerative anemia or neutropenia
b. Thrombocytopenia without shift platelets. Bone marrow evaluation is not recommended for presumptive immune-mediated thrombocytopenia or for DIC. However, if the patient is a suspect ITP and has not responded as expected to standard immunosuppressive therapy, bone marrow evaluation can then be considered.
2. Increased peripheral blood cell counts or atypical cells in circulation.
3. Hemolytic anemia in senior dogs that are at risk for neoplasia (example: Golden retriever, Bernese mountain dog).
Bone marrow aspirate may also be indicated due to abnormalities found on a biochemical profile such as Monoclonal gammopathy to investigate for multiple myeloma or Unexplained hypercalcemia to investigate for neoplasia.
The bone marrow aspirate is also helpful in monitoring response to therapy. For instance, if a patient is undergoing therapy for multiple myeloma or lymphoma and after achieving remission, has unexplained neutropenia or progressive thrombocytopenia, a recheck bone marrow aspirate may be warranted to discern between chemotoxicity and relapse. Similarly, a patient undergoing therapy for IMHA or ITP that initially responded to immunosuppressives may develop low counts of red blood cells or platelets and a bone marrow aspirate could help determine if the cell counts are dropping due to immune-mediated disease targeted at the bone marrow or due to bone marrow suppression from medications such as azathioprine or leflunomide.
Complications are rare and include hemorrhage, infection, fracture, and needle breakage at site of procedure.
Following the procedure, discomfort from the procedure is an expected complication and analgesics are prescribed at discharge. Bone marrow aspirate and biopsy can be safely performed in the thrombocytopenic and coagulopathic patient.
Bone marrow aspirate versus core biopsy
These procedures are typically performed at the same time and the samples can be used for different types of diagnostics and therefore provide different types of information.
Aspirates yield samples for cytology as well as for PCR and flow cytometry and testing for infectious disease (IFA, PCR, Culture). Biopsies yield samples for histopathology as well as for testing of infection. Bone marrow biopsy is most often obtained at the time of the aspirate procedure. This sample may be submitted at the same time as the bone marrow aspirate (especially if at time of procedure, preliminary evaluation of the aspirate in-house reflects a hemodilute or hypocellular, potentially non-diagnostic sample). If finances are a concern and if the bone marrow aspirate is hypercellular and likely to reveal the diagnosis, the obtained bone marrow biopsy sample can be held for submission at a later date if necessary. Core biopsy allows evaluation of bone marrow architecture and can diagnose myelofibrosis and inflammation.
At the time of bone marrow submission to the lab, an EDTA tube of peripheral blood is submitted with the bone marrow sample; this sample of peripheral blood will help the pathologist with interpretation of bone marrow activity in response to status of peripheral blood. If the patient has been transfused, a pre-transfusion sample (ideally within 24 hrs of the bone marrow sampling) is submitted.
The bone marrow sampling procedures can be performed on an outpatient basis if the patient is stable.
The patient will be sedated or placed under general anesthesia. Bone marrow procedures tend to be more difficult in small dogs and cats. If multiple sites are needed (which may not be known until the time of the procedure), procedure time may be longer and therefore, general anesthesia may be most ideal.
The most commonly used sites for aspirate and biopsy are the proximal humerus and iliac crest. Proximal femur, sternum, and costochondral junction may also be used for aspirate; bone biopsy cannot be performed on the sternum or costochondral junction. If there is a focal lesion of abnormality identified on radiographs, that site is also sampled.
For the procedure, the bone marrow sampling site is clipped and scrubbed. Lidocaine is administered to the level of the periosteum. Bone marrow aspirate is obtained with a 16-18 gauge bone marrow needle; I prefer a 16 gauge). The syringe and bone marrow aspirate can be primed with EDTA to help prevent clotting of the sample in the needle and syringe. Alternatively, an experienced team member typically assists in smearing bone marrow aspirates for me. At least 10 slides are made. If collecting for other diagnostics (PCR, other), a larger volume can be collected and transferred to a purple top tube. Core biopsy can be performed with a 11-13 bone marrow biopsy instrument.
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Illinois bone marrow
aspirate needle |
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Rosenthal bone marrow
aspirate needle
(this one is my favorite!) |
Several types of bio
psy instruments are available; I prefer to use the Snarecoil biopsy instrument. Following the proc
edure, a bone marrow aspirate slide is stained
and examined for presence of megakaryocytes. If none are present, the bone marrow aspirate is repeated at a different site. If the second site's cytology is similar to the first and I am confident that I was seated well into the bone, it is possible that significant marrow disease is present (myelofibrosis) and the bone marrow biopsy will then be
submitted. The patient is discharged with an appropriate analgesic, NSAID or opioid. If there is a possibility that glucocorti
oid therapy may be initiated based on cytology or biopsy results, an NSAID is not
prescribed.
If the patient is unstable and anemic and requires hospitalization and transfusion, a pre transfusion EDTA sample of peripheral blood is first collected, the patient is transfused, and the bone marrow aspirate/biopsy can then be pursued as described above.
