Blood partitioning method

Claim 1

In the method of separating blood into its light, substantially liquid phase and its heavy, substantially cellular phase by providing a tubular blood collection container having disposed in its bottom an inert, flowable, gel-like barrier material; filling the container with blood; and centrifuging the blood filled container to effect separation of the phases and displacement of the barrier material to the interface between phases; the improvement which consists of providing means to cause said gel-like barrier to make a complete sealing contact with the entire inner surface of the tubular container at a predetermined level thereof, said means consisting of a constriction in the bore thereof, positioned in the zone where the barrier material is calculated to come to rest during centrifugation, said constriction being integrally formed and fixed in the wall of the said container; whereby during centrifugation, the barrier material displaced makes sealing contact with said constriction and closes the bore in said zone, permanently isolating the liquid phase from the cellular phase without destruction of the tubular container.