Centrifuged material layer measurements taken in an evacuated tube.

Centrifuged material layer measurements are made in an evacuated glass or clear plastic tube (2) which contains a float (6). When possibly contaminated materials, such as blood, are being tested the use of the evacuated tube allows the measurements to be made without the technician being exposed to the blood. The tubes are large enough to hold approximately one ml of blood, and are filled with an inert gas at low pressure. Dimensional tolerances relative to those of a capillary tube are relaxed for the tube and float due to the larger sample capacity. The cell bands (32) are stabilized by a layer of a flowable material which settles onto the plasma layer (34) during centrifugation and forms a pellicle thereon.