Patent ID: 8012742

Claim:
A method of separating and axially expanding buffy coat constitutents 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 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; wherein 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 defines an annular volume therebetween; and wherein said support members traverse said annular volume to produce one or more analysis areas; creating a pressure differential such that the pressure inside the tube exceeds the pressure outside the tube to cause a resilient enlargement of the sidewall to a second diameter, 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 constitutents of the blood sample; and thereafter removing the pressure applied to the inside of the tube to cause the tube sidewall to return to said first diameter, thereby capturing the float and trapping the buffy coat constitutents in the analysis area.