Skills Laboratory: How to collect diagnostic bone marrow samples - Veterinary Medicine
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Skills Laboratory: How to collect diagnostic bone marrow samples
Bone marrow evaluation can help reveal the cause of abnormal blood work results and much more. Get good samples by following these steps for bone marrow aspiration and core biopsy.


Sample review and submission

Figure 11A. Note the highly cellular spicule with abundant iron (white arrows), several large megakaryocytes (black arrows), a heterogeneous population of hematopoietic cells, and large, lipid vacuoles.
Before moving the patient to recovery, stain and examine one slide to ensure sample adequacy. Diff-Quik stain (Dade Behring) or another rapid stain is acceptable for this review. On gross examination of the stained slide, a high-quality cellular sample should contain several small, deep-blue streaks within a pink background of blood (Figure 10). On microscopic examination, there should be several dense blue spicules surrounded by monolayers of hematopoietic cells (Figure 11A). If the smear is poorly cellular (Figure 11B), a second aspiration should be attempted slightly away from the original collection site or from a different site. If a cellular aspirate cannot be obtained, collect a core biopsy sample at this time as the marrow pathology may preclude collection of a cellular aspirate.

Figure 11B. The microscopic appearance of a poorly cellular spicule, which may be secondary to poor sampling or reflect true hypocellularity.
Label and submit two to four unstained slides containing the bone marrow aspirate to a veterinary clinical pathologist along with the results of a recent complete blood count, preferably performed at the same time as the aspirate, and a blood smear. Accurate interpretation of a bone marrow sample depends on knowledge of the peripheral hematologic findings. Include the patient's signalment, a brief history that includes information about previous and concurrent illnesses and recent drug therapy and the reason for taking the aspirate on the submission form. If bone marrow core biopsy samples in buffered formalin accompany the aspirate, the formalin vial and cytology slides must be completely isolated from one another because formalin vapors will fix the cytology slides, rendering them unstainable. Additional unstained smears should be submitted if special stains are requested (Prussian blue for iron) or anticipated (cytochemistry or immunochemistry for determination of lineage in leukemias).

Nondiagnostic samples

Low-cellularity or poor-quality samples may be a result of inadequate technique, including improper seating of the needle in the marrow cavity, excessive aspiration resulting in hemodilution, or sample clotting before slide preparation. However, several pathologic conditions prevent acquisition of cellular marrow aspirates. Myelofibrosis often results in poorly cellular samples because of abundant collagen and reticulin fibers. Aspirates from patients with aplastic anemia typically yield only adipose tissue with few poorly cellular to no hematopoietic spicules. In cases of myelofibrosis or aplastic anemia, core biopsies are required to identify the presence of fibrosis or the replacement of hematopoietic tissue by adipose tissue, respectively. As mentioned in the introduction, bone marrow aspiration and core biopsy are complementary techniques, so providing both samples will maximize the diagnostic information.


Figure 12A. Once the needle has gained purchase in the cortex, remove the stylet. Then drive the biopsy needle into the medullary cavity in a manner identical to collecting an aspirate.
A bone marrow core biopsy can be performed from the same bone by selecting a site a few millimeters away from the aspiration site, permitting preparation of a single site. Alternatively, the biopsy sample can be obtained from a different site. Biopsy sampling from the ilium can be performed by using the same approach as for aspiration or by using a lateral-to-medial approach through the dorsal aspect of the wing.7,9 The latter may be preferable in cats and small dogs with thin ilial wings.


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