1. Field of the Invention
This invention relates to blood separation devices, and more particularly relates to blood centrifuges having a spun rotor. Even more specifically, this invention relates to rotors for high speed blood centrifuges.
2. Description of the Prior Art
FIGS. 1, 1A, 2 and 3 are various views of a hematocrit rotor 2 used in a high speed spinning centrifuge used primarily for in vitro diagnostics and incorporated in the VetTest™ veterinary blood analyzer manufactured and sold by Idexx Laboratories, Inc. of Westbrook, Me.
The rotor 2 is generally cylindrical in its overall outer shape, and includes a housing having 3 an upper portion 4 joined to a lower portion 6. The upper portion 4 and lower portion 6 define between them an interior chamber 8 or well for receiving a sample of whole blood. For this purpose, the upper portion 4 is provided with a central fill port 10 communicating with the interior chamber 8 so that a user may supply a blood sample from a pipette through the port 10 and into the chamber 8 prior to centrifugation and, conversely, withdraw plasma collected in the chamber 8 after blood separation has been completed.
The rotor 2 includes a silicone gel 12 situated circumferentially about the interior chamber 8 above the lower portion 6, which gel 12 captures or absorbs the denser blood cells from the sample, but not the plasma, when the rotor 2 is spun at high speeds. After centrifugation, the plasma collects in the lower portion 6 of the rotor 2 where it may be retrieved through the port 10 in the upper portion 4 by using a pipette.
A problem arises with the rotor described above in that it may be overfilled with the whole blood sample. The amount of gel 12 provided about the interior of the rotor 2 can only absorb a certain quantity of blood cells for a given volume of blood sample. Accordingly, if the rotor chamber 8 is overfilled, the whole blood sample may exceed the capacity of the gel to absorb the denser cells. Thus, not all of the blood cells will be absorbed by the gel 12 upon centrifugation, resulting in blood cells remaining in the plasma. This may affect the accuracy of subsequent diagnostic tests and especially colorimetric measurements performed on the plasma and provide uncertain and possibly inaccurate analytical results.
Although instructions are provided with the VetTest™ analyzer on the proper use of the centrifuge and the correct volume of whole blood sample with which to fill the rotor, the clinician or user may unknowingly overfill the rotor with whole blood, resulting in an unseparated blood cell component remaining in the plasma after centrifugation.