This invention relates to blood collection devices and, more particularly, to the reduction of cell contamination of the separated lighter blood phase in a blood collection device.
It is common practice to employ a collection tube for receiving a whole blood sample from a patient whose blood is to be clinically tested, and then to centrifuge the filled tube to separate the blood into its lighter phase, serum or plasma, and its heavier cellular phase. In some cases, well known automatic or centrifugally activated phase partitioning devices or materials are placed in the tube which provide a liquid-impervious barrier between the separated phases after centrifugation. The barrier maintains the light phase isolated from the cellular phase components and facilitates subsequent removal of the light phase from the tube free of red cells.
However, red blood cells often adhere to surfaces of the stopper within the tube after the phases have been separated so that such cells remain in that portion of the tube which contains the separated lighter phase. These cells may come in contact with the light phase during handling or during removal of the stopper and light phase from the collection tube, and can contaminate the light phase such that some clinical tests performed produce inaccurate and unreliable results.
In an attempt to prevent blood cells from adhering to the stopper, the stopper has been shaped so that cells contacting it will have a tendency to to slide off. However, such shaping of the stopper has not been entirely satisfactory. U.S. Pat. No. 3,958,572 illustrates a stopper shaped to reduce the chance of cells adhering to the inner side of the stopper. This method requires a special stopper construction and still does not insure against the adherence of cells to the stopper. It is also mentioned in that patent that if the stopper is made of rubber, then silicone oils or glycerine solutions can be used as lubricants for easy insertion and removal of the stopper, and that such treatment also gives added protection against cell or clot adherence to the stopper. However, coating stoppers with a lubricant has generally not been an effective solution to the prevention of cell adherence to the stopper and cell contamination of the light phase.
In U.S. Pat. No. 3,882,021, a phase partitioning piston remains in its initial position and is sealed against contact with the blood by a frangible seal to prevent contamination of the piston by blood cells during phase separation. Upon increased centrifugal force, after phase separation, the seal is broken and moves to the bottom of the tube, and the piston slides to a position adjacent the interface of the light and heavy phases. This device employs a relatively expensive tube assembly having a stopper in each end. It also requires the operator to centrifuge the tube at one speed until phase separation has taken place, and then to increase the speed in order to break the frangible seal. Thus, such a frangible seal arrangement results in a rather complicated separation procedure and a relatively expensive device.