Some pathologists prefer their bone marrow smears to be made fresh at bedside without the use of any anticoagulants. This however limits the number of smears that can be made before the sample clots.
Using a syringe, that has been rinsed with preservative-free heparin, to pull the marrow during the procedure will prevent clotting but will introduce morphology changes and staining artifact.
It is preferable to make smears as soon as possible after sample collection. However, when stored in the refrigerator, acceptable smears can be made from an EDTA tube until about 8-10 hours after sample aspiration without introducing excessive amounts of artifacts. This is useful when marrows are collected at times when staffing trained in marrow smear preparation may not be available.