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Abstract

A shatter-proof fluid sample container adaptable for use with a centrifuge is provided. The fluid sample container is especially useful for expanding layers of a fluid sample, such as a blood sample, that form during centrifugation. The fluid sample container includes at least one fill well, a reagent pellet well including a reagent pellet containing reagents and dyes, a mixing channel, a distribution cavity which distributes the fluid to a plurality of expansion cavities, and a float cavity which includes a constant density precision molded float. As the fluid is centrifuged in the fluid sample container, the fluid contacts and dissolves the reagent pellet, and flows through the mixing channel where the material in the reagent pellet mixes with the fluid. The fluid collects in a distribution cavity until the rotational speed of the centrifuge is increased to impose a centrifugal force on the fluid sufficient to cause the fluid to flow over a ramped portion separating the distribution cavity from the plurality of expansion cavities and the float cavity. The expansion cavities each include a portion having a cross-sectional area smaller than the cross-sectional area of any other portion of the expansion cavity. The area having the smaller cross-sectional area has the effect of expanding certain component layers formed in the centrifuged sample, thus making the boundaries of those component layers, such as the buffy coat layers in a blood sample, more readily ascertainable and thus easier to read with an optical reader. The float cavity contains a float having a controlled density such that it centers itself on the buffy coat region when the blood cells are packed by centrifugal force. The depth of float penetration into the packed red blood cells is a function of the RBC density. Since the RBC density is proportional to hemoglobin concentration, the instrument can calculate % Hg from float depth.

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