The oldest blood available for transfusions releases large and potentially harmful amounts of iron into patients’ bloodstreams, warns a new study. The study recommends reducing the maximum storage limit of red blood cells from six to five weeks.
Researchers at Columbia University Medical Centre (CUMC) in the US randomly assigned a group of 60 healthy volunteers to receive a unit of red blood cells that had been stored for one, two, three, four, five or six weeks.
The volunteers were then monitored for 20 hours after transfusion. Within hours after transfusion, seven of the nine volunteers who received the six-week-old blood could not appropriately metabolise the damaged cells, thereby releasing large amounts of iron into their bloodstream.
Only one volunteer who received younger blood had a similar response, with blood had been stored for five weeks.
“Our recommendation will be controversial, but we think we have real data to support it,” said Steven Spitalnik from CUMC.
“Recent studies have concluded that transfusing old blood has no impact on patient outcomes, but those studies did not exclusively examine the oldest blood available for transfusions,” said Spitalnik.
Our new study found a real problem when transfusing blood that is older than five weeks,” Spitalnik added.
Transfusion of red blood cells is the most common procedure performed in hospitalised patients, with about five million patients receiving red blood cell transfusions annually in the US.
“However the longer you store blood, the more the cells become damaged,” said Eldad Hod, associate professor at CUMC.
Currently, the US Food and Drug Administration (FDA) allows units of red blood cells to be stored for up to six weeks before they must be discarded.
None of the volunteers were harmed by the transfusion, but previous studies have shown that excess iron can enhance blood clots and promote infections.
“Based on the amount of iron circulating in the blood of the volunteers who received six-week-old blood, we had predict that certain existing infections could be exacerbated,” said Hod.
“Thus, for ill, hospitalised patients, this excess iron could lead to serious complications,” said Spitalnik.
The true impact of six-week-old blood on the rate of complications in patients is likely to be small, said the researchers.
“It is estimated that up to 10 to 20 per cent of blood units used for transfusions have been stored for more than five weeks, so the number of patients who are likely to receive a unit of very old blood is substantial,” said Hod.
The study appears in the Journal of Clinical Investigation.