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.


VETERINARY MEDICINE



Figure 1. A bone marrow aspiration needle (left) and a Jamshidi biopsy needle (right) are shown with the stylets removed. The Jamshidi biopsy needle narrows at the tip to retain the sample within the needle bore. To remove the biopsy sample, the crooked wire is inserted retrograde into the needle to push the core through the wider, proximal end.
A basic marrow aspiration or biopsy needle consists of two pieces: a hollow needle portion with a proximal collar and a solid stylet that fits the needle bore (Figure 1). The stylet usually has a notch that locks it into the collar of the needle portion. Most needles also have a cap that fits over the proximal end to maintain sterility and facilitate handling.

Additional supplies are common to every clinic. A watch glass, Petri dish, or similar container can be used to separate and collect bone marrow particles from the harvested sample before making smears.

COLLECTION SITES AND PATIENT PREPARATION

Hematopoiesis is most active in the flat bones, such as the skull and ribs; however, bone marrow is collected from sites that are more easily and safely accessed. These include the greater tubercle of the proximal humerus, the iliac crest of the pelvis, and the trochanteric fossa of the proximal femur (Figure 2). Site preference depends on patient conformation and body condition. Precise landmarks and animal positioning are described in the procedure section below.


Figure 2. Bone marrow collection sites. (A) The greater tubercle of the proximal humerus. (B) The iliac crest of the pelvis. (C) The trochanteric fossa of the proximal femur.
General anesthesia may be required for fractious animals, but heavy sedation is adequate in most patients. Shave and surgically prepare the site, and perform a local anesthetic block of the skin, subcutaneous tissues, and periosteum with 1% to 2% lidocaine. Endosteal innervation remains intact and is the site of pain on aspiration. Bleeding is typically minimal and requires only local compression when the procedure is completed. If necessary, provide postprocedural analgesia with nonsteroidal anti-inflammatory agents given short-term.

BONE MARROW ASPIRATION AND SLIDE PREPARATION

There are three keys to collecting high-quality bone marrow aspirates:
1. Place the needle securely within the marrow cavity.
2. Avoid hemodilution.
3. Prevent clot formation once the sample is obtained.

Procedure

Wear sterile surgical gloves when handling the aspiration needle and collecting samples. Small surgical drapes around the site help maintain a sterile field. To facilitate passage of the aspiration needle, make a small stab incision in the skin over the aspiration site with a No. 11 scalpel blade.


Figure 3. Hold the collar of the aspiration needle securely between your thumb, index, and ring finger to provide fine control and stability. With the cap in place, lodge the proximal end of the instrument tightly against your first metacarpophalangeal joint.
A secure grip on the biopsy needle is fundamental to placing it correctly within the marrow cavity. With the stylet locked in place, hold the needle in a modified pencil grip for precise control (Figure 3). Securely lodge the proximal end of the biopsy instrument against the palm of your hand or against the first metacarpophalangeal joint. This contact keeps the stylet in place and permits generation of the force necessary to penetrate the cortex, while the fingers provide stability and control. Compressing the skin and soft tissue around the site with the opposite hand also improves stability.


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Source: VETERINARY MEDICINE,
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