Are blood transfusions always venous blood rather than arterial?

During a friend’s blood transfusion it was noticed that one bag had bright red blood and the other dark red blood. Is it possible that the bright red blood was draw from an artery vs the other from a vein?

Submitted by Sonia from Huntington Beach, California on 05/14/2016

by Arthur Bracey, MD

Blood immediately collected from an arterial source is bright red in color due to the effect of oxygen binding the ferric-heme complex. Any blood stored over time – including the interval normally required for blood processing prior to transfusion – undergoes metabolic change to render it into a non-oxidative state of metabolism. Hence, any oxygen would be consumed and an unlikely source of bright coloration at the time of infusion. This does not eliminate other unusual reasons for the observed difference in color which would all be speculative at this point in time.