The present invention relates to bags for use in the preservation of blood cells.

Blood used for transfusion is normally stored in refrigerators, where its safe life is only five weeks. Potentially longer storage life might be obtained by freezing, but unfortunately freezing blood as obtained from a donor results in destruction of the red blood cells making the blood totally unsuitable for transfusions. Red blood cells can be stored after separation, by centrifuging, from the associated plasma, mixing with a cryoprotectant, and then freezing. The usual cryoprotectant is glycerol. As glycerol itself is poisonous frozen cells must have all the glycerol removed therefrom before being used for transfusion, and the necessary washing process is a skilled and time-consuming task which usually results in a significant loss of usable cells. Another cryoprotectant is hydroxyethvl starch (HES) , which is non-toxic, and much work has been carried out on methods of preserving red blood cells using this substance. Early efforts were unsuccessful, as it was found that the level of haemolysis (breakdown of red blood cells) in units of blood (a unit of blood being the volume of a standard donation, about 450ml) recovered after freezing was above the safe limit. It is usually considered that to be safe for transfusion the level of haemolysis should be no greater the- 1% . A method of preserving and recovering red blood corpuscule Dy freezing, using HES as a cryoprotectant, wherein the level of haemolysis after recovery is within acceptable limits, has now been developed and is described in Patent Application PCT/GB90/0140.

The bags used in the method of PCT/GB90/0140 must be capable of fulfilling stringent criteria. Freezing is carried out in liquid nitrogen, and the manner in which the unavoidable changes in volume of the mixture of red blood cells and cryoprotectant during freezing are accommodated must be carefully controlled. It is also important that the concentration of HES is within stringent limits, and that the donation process is carried out in a sterile manner.

It has been suggested that the HES be stored in the freezing bag itself. However it has been found that materials, suitable for the bag tend to be slightly porous, so that the moisture content of HES within a bag varies during storage, the nature of the variation being dependant on the atmospheric humidity of the store.

It is also important that the bags, which must, of course, be stored at sub-zero temperatures, should be of a convenient shape for storage, and that it should be possible to directly tap into a bag for transfusion purposes. Bags which fulfil this criterion are described in Patent Applications PCT/GB88/00947 and PCT/US91/00192. The manner of extraction from these involves penetration by a needle of the bottom fold of a pouch which extends inwardly of the bag. This procedure requires equipment which is not standard, and also requires new skills to be learnt by personnel giving transfusions. According to the present invention a freezing bag has an inlet port connected to an inlet tube to characterised in that the inlet tube is connected a cryoprotectant storage bag having an impervious cover, and an outlet port, the inlet tube and the outlet port each having a breakable seal. The impervious cover might be the actual material of the bag, or might be a separate cover surrounding the bag.

The bag will normally be of generally rectangular, usually square, shape. The inlet port and outlet port will usually be on the same edge of the bag, with the outlet port preferably towards the centre of the edge, advantageously being slightly offset from the centre.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, of which: Figure 1 is a view of a bag according to the invention, and

Figure 2 is a view, in section along line II-II of Figure 1, of a cryoprotectant storage bag.

A freezing bag 10 (Figure 1) suitable for use with the method of PCT/GB90/140 has, situated at one end of an edge 20, an inlet port 11 connected to a tube 12 having a breakable seal 13- A branch 14 from the tube 12 leads to a cryoprotectant storage bag 15 which is surrounded by a cover 16 (see Figure 2) made of impervious material.

The cover 16 extends for a sufficient length of the branch 14 to insure that it will overlie any position to which cryoprotectant will penetrate.

At approximately the centre, but slightly offset from the centre, of the edge 20 is an outlet port 17 having a breakable seal

18. The outlet port 17 and seal 18 might conveniently be of the type used on conventional (non- frozen) storage bags.

In use the cover 16 is removed from the cryoprotectant storage bag 15 and the breakable seal 13 removed from the tube 12, which is connected to a red blood cell supply (not shown) in known manner.

Blood from a donor is centrifuged and the red cells therefrom passed through the tube 12 to the bag 10, cryoprotectant from the cryoprotectant storage bag 15 being passed through the branch 14 and tube 12 at the same time. The bag is then sealed, for example by thermally sealing along a line 19, in known fashion, and then removing the inlet port 11 and associated items. The bag 10 is then shaken to mix the red blood cells and cryoprotectant, frozen and stored according to the method of PCT/GB90/140.

When it is required to use the stored blood it is defrozen according to the method of PCT/GB90/140, the breakable seal 18 removed, and the outlet port 17 connected to transfusion means in the standard way.

It will be realised that with the outlet port 17 offset from the centre of the edge 20 a number of bags 10 may be stored in "back to back" fashion, such that adjacent ports 17 do not overlie, reducing the storage space required for a number of bags.

Many variations of the invention will be apparent to those skilled in the art. For example the cryoprotectant storage bag 15 might be formed of impermeable material, there then being no need for a separate cover 16. However this arrangement makes it harder to protect cryoprotectant entering the branch 14.

Materials suitable for use with the bag 10 and other items will readily be apparent to those skilled in the art. For example, many plastic materials having the required flexibility and suitability for use at low temperatures, are available commercially, and metallised plastics material may also be used.