Blood collecting syringe

Abstract

An article for drawing a blood specimen comprising a specimen-receiving tube having a closed end and an open end, a resilient expandable plug received in the closed end portion of the tube in normally relatively light sealing engagement with the side wall structure of the tube, and an elongated cannula holder having a through longitudinal passageway for communication with the interior of the cannula, the plug and the holder having co-acting means for releasably coupling the plug and the holder when the holder passageway is in communication with the closed end portion of the tube through the plug, the holder expanding the plug into relatively firm sealing engagement with the tube side wall structure. The holder may be uncoupled from the plug when the tube is filled with the specimen and the plug occupies the open end of the tube. The tube and its contents including the plug may be placed in a centrifuge. The plug may have a specific density intermediate those of the plasma and cell portions of the specimen and, when a centrifugal force is applied sufficient for separation of such specimen portions, the plug in seeking its own specific density level in the tube is deformed and moved downwardly in the tube. When such force is removed after such separation, the plug provides a plasma-cell barrier.