Blood banking involves the collection of blood from donors and the storage of that blood until it is required for transfusion. It is usual to distinguish, in a blood banking system, between central blood banks whose functions are primarily those of collection and distribution, and hospital blood banks which perform the process of cross‐matching. In order to ensure that the donor's blood will be compatible with that of the recipient, blood is cross‐matched by mixing a sample of the recipient's blood with a sample of stored blood of the same group and subjecting the mixture to certain tests.