Countless lives have been saved since blood transfusions were first introduced in the seventeenth century. Initially, some members of the medical community were hesitant to use them, but transfusions were soon seen as vital in the replenishment of blood lost through trauma, illness or in the operating theatre. In many ways, transfusions are a medical marvel, providing a safety net for times when procedures don’t quite go according to plan. Transfusions also represent a lifeline for people with inherited blood disorders, with certain rare diseases or who are undergoing chemotherapy. But the field of transfusion medicine is changing. Instead of seeing it as an inert recharging of fluid, we’re now coming to appreciate that a blood transfusion is essentially a liquid ‘organ transplant’, which comes with its own risks and drawbacks.
Blood occupies a strange and somewhat privileged position in modern medicine, and it has evolved as a treatment option without the same level of research scrutiny – at least on the patient outcomes side of things – that other treatments are subjected to. Nowadays, if you have a modern pharmaceutical it goes through the whole process of clinical trials before it’s registered, but blood didn’t come to health that way. As far back as 1990, studies were hinting that blood transfusions carried more risks than had previously been thought, and it was quickly becoming apparent that the mere fact a patient received a blood transfusion was a risk factor and in some instances was associated with poorer outcomes.
Research up to now has been far from comprehensive. ‘Restrictive transfusion’ studies – where a transfusion was only given if a patient’s haemoglobin levels dropped to a certain point – did not appear to leave the patient any worse off. In a perfect world, however, scientists would do a clinical trial. People would be randomly assigned to one of three groups – some would have a blood transfusion, others would be given a placebo and others no transfusion at all. Scientists would then compare how each group fared. But a trial such as this would never get approved, because why would you give a blood transfusion to someone who didn’t need one, even in a clinical trial setting? By the same token, why risk not giving blood to someone who might well die without it?
Another way of testing the pros and cons of blood transfusion involves consent. Fully informed patients are well within their rights to refuse a blood transfusion if they feel it conflicts with cultural, religious and personal beliefs. Such patients have inadvertently served as a sort of test case. This situation, in which transfusion is no longer an option for doctors, has given rise to some surprising results when the patient makes a better than expected recovery following surgery. Some commentators have suggested that the option of transfusion being unavailable may have led surgeons to proceed in a more cautious manner, which resulted in positive changes in surgical technique that led to improved outcomes. Another interpretation, however, could be that the transfusion itself was doing more harm than good.
When it comes to extracting and identifying the negative consequences of blood transfusion, medical researchers still have a challenge ahead of them. The reason is that if someone is considered sick enough to need a transfusion, there’s a good chance they’re already in a bad way physically. This makes it virtually impossible for anyone to say with any degree of conviction that a patient’s state of health is caused by the blood transfusion or is the result of the illness and trauma that led to them receiving the blood transfusion in the first place. What is known is that the observational studies have pointed to a longer time spent in hospital, a higher risk of infection after surgery, an increased likelihood of needing artificial ventilation, and a greater risk of needing transfer to the Intensive Care Unit with conditions such as multi-organ failure. Such evidence is tenuous to say the least, and therefore the jury is still out.
A growing body of research data from laboratory and animal studies is giving insights into what transfused blood does to the host body. Take the fact that blood transfusions were once used to prepare recipients for kidney transplant, because transfusions were known to reduce the likelihood that the host immune system would reject the donor organ. This suggests that donor blood is somehow modifying the host’s immune system; a desirable effect in the early days of kidney transplants, but less desirable if a patient is in intensive care after an accident and already physically vulnerable.
There’s also the suggestion that the more blood a patient gets, the more problems they are likely to have. However, even one unit of blood is enough to cause problems, so such concerns may be misplaced. More significant is the fact that storing donated blood outside the body changes it. Chemical messengers called cytokines, and other biological substances, accumulate in stored blood, and there’s the possibility that this may cause issues when the blood is transfused into the patient.