Abstract
Background
Doctors and healthcare professionals often give blood transfusions to people after loss of blood from surgery, bleeding, or medical illnesses. Blood is a limited resource, so for this reason, and because some low‐income countries do not test the blood used in transfusions for the presence of dangerous viruses such as HIV or hepatitis, it is helpful to give blood transfusions only when they are really necessary.
A normal blood count is above 12. This review summarised all randomized controlled trials (RCTs) that investigated whether it is safe to give blood transfusions when the blood count drops to between seven and eight (thereby reducing the number of transfusions), rather than giving transfusions at higher blood counts of nine to 10.
Study characteristics
We examined the results of RCTs that randomly allocated participants to one of two groups. In one group, trial participants received blood at lower blood counts. In the other group, trial participants received blood at higher blood counts. The data are current up to May 2016.
Key results
We identified a total of 31 relevant trials, which involved 12,587 participants. All of the studies compared different policies for blood transfusions. We found that participants who were assigned to receive blood at lower blood counts were 43% less likely to receive a blood transfusion than those who were given blood at higher blood counts. The risk of dying within 30 days of the transfusion was the same whether the participants received transfusion at lower or higher blood counts. We also evaluated harmful events that occurred after participants received, or did not receive, blood transfusions, including infection (pneumonia, wound infection, and blood poisoning), heart attacks, strokes, and problems with blood clots, and found that there was no clear difference in the instance of these events between the group that received transfusions at lower blood counts and the group that received transfusions at higher blood counts.
Quality of evidence
We found that most of the RCTs provided a high quality of evidence, in that they were adequately conducted and used appropriate methods that minimised any possible biases that could make the validity of the results uncertain.
Authors conclusions
We concluded that it was not harmful to the participants' health status to give blood at lower or higher blood counts. If a policy of giving blood only at lower blood counts were followed routinely in clinical practice, it would reduce the amount of blood patients receive substantially and reduce the risk of patients receiving blood transfusions unnecessarily, as transfusions can have harmful effects. Additional studies are needed to establish the blood count at which a blood transfusion is needed in patients who have suffered a heart attack, brain injury, or have cancer.