Complication and mortality rates increase following heart surgery if older blood is transfused during the procedure, according to a new study from the Cleveland Clinic.

The study concluded that a patient was at greater risk for complications and even death if given blood that had been stored for two weeks or longer.

Researchers looked at data from patients who had received blood during coronary-artery bypass grafting or heart-valve surgery, or both, over an almost eight-year period.

Almost 2,900 patients in the study received blood that had been stored for two weeks or less (newer blood), and just over 3,100 patients received blood that had been stored for more than two weeks (older blood).

Patients who received older blood were:

• more likely to die in hospital (2.8 per cent vs. 1.7 per cent)
• more likely to have kidney failure (2.7 per cent vs. 1.6 per cent)
• more likely to have to be intubated for longer than 72 hours (9.7 per cent vs. 5.6 per cent)
• more likely to contract a blood infection (4 per cent vs. 2.8 per cent)
• had a greater chance of not living past their first year after surgery (11 per cent vs. 7.4 per cent)

But Dana Devine, vice-president of medical, scientific and research affairs for the Canadian Blood Services, said that while the statistics show that more investigation into this issue is needed, the numbers aren't alarming.

"If this were a huge difference we would be very concerned immediately and we would be looking hard at what we could do differently today," said Devine.

Red blood cells, which deliver oxygen throughout the body and help eliminate waste, undergo changes during storage that compromise their effectiveness. However, blood cells age in storage just as they age and die off in the human body - transfused cells would simply join this cycle.

"A blood transfusion is always a stop-gap measure until your body starts to make enough of its own red cells again," said Devine.

It is estimated that about half of all heart surgery patients require a blood transfusion during surgery. However, techniques have improved such that surgeons transfuse as little blood as possible. When a patient is bleeding, blood cells are often collected, cleaned and put back into the patient.

Based on the findings, the study recommends that blood be considered unusable earlier than the current 42-day threshold allowed by the United States Food and Drug Administration and Health Canada.

But that guideline was established after manufacturers of blood-storage containers put forth data to the FDA and Health Canada "that 42-day blood has the same kind of characteristics as when it had a 35-day 'out-date,'" said Devine.

Devine added: "And if you look at when blood is actually used, for the most part in transfusion it's used much sooner than 42 days. So that deadline is the far end of possibility."

However, said Devine, because the study looked at older patients who were having a very invasive procedure, it does raise the question of whether or not the age of the blood makes a difference to patients of different ages and medical circumstances.

The study is published in the New England Journal of Medicine.