It is important that the container is filled to the appropriate level when blood is collected into a microcollection container that has an anticoagulant. The device should then be capped and the blood mixed well immediately following collection of the specimen. The manufacturer of the containers that are used specifies what is considered adequate mixing and the laboratory's collection procedure should be based on these recommendations. Mixing involves a gentle tapping on a hard surface to move the blood further down into the tube during collection and then capping the tube upon completion of the collection so that the tube can be mixed end-over-end for the specified number of times as shown in the image.
The correct fill is also important. A container that is overfilled will not be properly anticoagulated and clots may form that will affect the laboratory test results. A container that is underfilled may not contain sufficient specimen to perform the test(s) or the excess anticoagulant may interfere with the test. For example, excess anticoagulant could cause morphologic changes in blood cells.