Transfusions of blood stored for more than two weeks cut survival rates and could pose complications for heart-surgery patients, a study found. The new study about the shelf life of blood says that blood deteriorates with age and that rules allowing blood to be stored for six weeks may pose a safety risk in some patients.

According to the latest research published in the latest New England Journal of Medicine, eighty-eight patients given blood that had been kept for an average of 20 days died in the hospital after surgery compared with 49 people who got transfusions of blood stored an average of 11 days. Patients receiving older blood also increase their chances of suffering from kidney failure and blood infections.

According to Colleen Koch, the study's lead author while the latest research won't lead to immediate changes to the expiration date of blood, results from a randomized trial that will be available in about two years might. A more rigorous study is already under way that could carry the scientific weight to persuade the Food and Drug Administration to reconsider its six week policy.

Researchers believe that stored blood becomes depleted of oxygen-carrying chemicals thus making it unsafe for certain patients. Red blood cells also become more rigid in storage, hindering their flow through the body.