Scientists have now found that the shelf life of blood is shorter than what was thought till now — three weeks and not six weeks.
Researchers from Johns Hopkins have found that red blood cells (RBCs) stored longer than three weeks begin to lose the capacity to deliver oxygen-rich cells where they may be most needed.
According to the investigators, red cells in blood stored that long gradually lose the flexibility required to squeeze through the body's smallest capillaries to deliver oxygen to tissue. Moreover, they say, that capacity is not regained after transfusion into patients during or after surgery.
"The study is telling us that the shelf life of blood may not be six weeks, which is what the blood banks consider standard," says study leader Steven Frank from Johns Hopkins University School of Medicine. The study has been published in the journal Anesthesia & Analgesia.
Frank acknowledges that blood banks do not have enough fresh blood for everybody, and that shorter storage periods would result in diminished inventory. But he says that the current practice of transfusing blood stored up to six weeks may need to be reconsidered. The finding is of vital importance for India which already faces an acute shortage of donated blood — to the tune of 2 million units a year. Less than 45% of donated blood is collected in developing and transitional countries, which are home to about 80% of the world's population . India requires 8.5 million units of blood annually but collects only about 6.5 million units.
For this study, Frank and his colleagues enrolled 16 patients scheduled to have spinal fusion surgery, an operation that requires blood transfusions. Six of the patients received five or more units of blood, while 10 needed three or fewer units. The researchers drew samples from every bag of blood used — 53 in total — and measured the flexibility of the red blood cells.
What they found is that blood older than 3 weeks was more likely to have less flexible red blood cell membranes, a condition that may make it more difficult for blood to deliver oxygen, Frank says.
The team also took blood samples from patients in the three days following surgery. Even though the blood cells were out of storage and back in biological environments with proper pH (acidity), electrolytes and oxygen levels, the injury to the red cells was not reversible and appeared to be permanent. The damaged blood cells would likely remain dysfunctional for their life cycle limit, which is up to 120 days, Frank says.
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