Patent ID: 7074577

Claim:
A method of separating and axially expanding buffy coat constituents of a blood sample, comprising: introducing the blood sample into a flexible sample tube, the sample tube having an elongate sidewall having a first cross-sectional inner diameter; introducing an elongate rigid volume-occupying float into the flexible sample tube, said rigid float having a specific gravity intermediate that of red blood cells and plasma; said float comprising: a main body portion and one or more support members protruding from the main body portion to engage and support the sidewall of the sample tube, said main body portion and said support members of the float having a cross-sectional diameter less than said first inner diameter of the tube when the sample tube is expanded, wherein said main body portion together with an axially aligned portion of said sidewall define an annular volume therebetween; and wherein said support members traverse said annular volume to produce one or more analysis areas; centrifuging the sample tube to effect a density-based separation of the blood sample into discrete layers at a rotational speed that causes a resilient enlargement of the sidewall to a second diameter in response to centrifugal force, said second diameter being sufficiently large to permit axial movement of the float in the tube; moving said float into axial alignment with at least the buffy coat constituents of the blood sample in response to centrifugal forces produced in centrifuging the blood; and thereafter, reducing the rotational speed to cause the tube sidewall to return to said first diameter, thereby capturing the float and trapping the buffy coat constituents in the analysis area.