A-Z of Bone Marrow Aspirates

Presenter – Adam Bell BSc BVSc CertVC CertSAM MRCVS of Calder Vets, and Nick Carmichael BVM&S, BSc VetSci(Hons), Diploma VCS(Syd), Diploma RC Path, Diplomate ECVCP, MRCVS, RCVS recognised specialist in clinical pathology, of Carmichael Torrance.

Learning the art of broncho-alveolar lavages (BALs) was last week’s treat and I was delighted to see bone marrow aspirates stealing the lime light for this week’s veterinary webinar. If I thought getting diagnostic samples from BAL’s could be tricky, bone marrow aspirates fall into the category of ‘really’ tricky, perhaps for the very reason that I just don’t do enough of them.

Adam Bell and Nick Carmichael from last week’s veterinary webinar led part two of this essential viewing and agreed that this is a technique which really does take practice, and using cadavers helps to acquire a consistent technique.

As for BALs, suitable collection of bone marrow aspirates is crucial, and Adam gave some great tips on how to achieve optimum results. Preparing pre-filled EDTA syringes prior to collection is a great way of ensuring that you have more time to deal with an aspirate and make smears prior to any deterioration within the sample.

These syringes can be made by filling a 10ml syringe with 1ml of sterile saline. An EDTA tube should be filled with this saline, capped and mixed. This should then be drawn back into the syringe and repeated with 2-3 more

EDTA tubes. This syringe will then be filled with EDTA rich saline. The technique for performing a bone marrow aspirate was demonstrated by Adam, whose preference is to use the iliac crest for collection, but the intertrochanteric fossa and greater tubercle can also be used dependant on personal preference. Confirmation may also play a role, for example, obtaining a sample from the intertrochanteric fossa may be easier in an overweight dog. Adam uses a Jamshidi type needle (13-16G in the dog, 16-18G in the cat) to perform a bone marrow aspirate. The patient should always be anaesthetised unless it is considered too risky, and a stab incision should be made over the appropriate area. The insertion site is immobilised and the needle inserted in a firm to and fro rotary action. Once the needle is within the correct position the patient should be able to be lifted from the table by the needle. The stylet is removed and the prefilled syringe is used to aspirate. It is crucial aspiration is stopped as soon as material in the hub is seen, hopefully lowering the risk of heamodilution.

Once an aspirate has been taken, Adam suggests getting a core biopsy by advancing the needle 1-2cms with a one way rotation without reinserting the stylet. Rock in place a few times and then withdraw. In some cases, a sample cannot be obtained on aspiration and it is necessary to either withdraw or advance the needle slightly. If still unable to obtain a sample then it is worth trying a different site. If, however, all samples are ‘dry’, a core biopsy is crucial in attempting to make any form of diagnosis.

Following Adam’s enlightening coverage on performing bone marrow aspirates, Nick Carmichael went on to discuss the reasons for performing bone marrow aspirates and their interpretation, citing a number of clinical cases. So after a duet of veterinary webinars and a duet of speakers, will I be twice as likely to obtain diagnostic samples from broncho-alveolar lavages and bone marrow aspirates? I’m not so sure about twice as likely but I’m fairly confident I’ll be going in the ‘more likely’ direction, thanks yet again to ‘The Webinar Vet’.

The Stethoscope (MRCVS)

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