27th May 2023

Red blood cell transfusion

Indications

Red cell transfusion is an essential tool in clinical medicine. In an actively bleeding patient, transfusion can prevent circulatory collapse and maintain tissue perfusion. In a patient with acute ischaemia, it can improve tissue oxygen delivery, relieve symptoms, and prevent complications. In a patient with chronic anaemia, it can relieve symptoms and improve quality of life. Blood product transfusion is, however, associated with significant potential risk and high cost. Judicious stewardship and selection of blood products is critical.

The decision to transfuse red cells is based on clinical assessment of the patient, as well as a full blood count (FBC) value. As a result, there is no universal trigger for transfusion and instead a patient-centred decision must be made. However general principles apply:

• In the haemodynamically stable, non-bleeding patient, transfusion should be considered if the haemoglobin (Hb) is 80g/L or less.
• If the Hb is below 70g/L, transfusion is usually indicated.
• Higher thresholds may be appropriate in individual cases, for example an anaemic patient with ischaemic heart disease and chest pain.
• In patients with gastrointestinal bleeding, once haemodynamically stable, over-transfusion may increase the risk of recurrent bleeding by increasing portal venous pressure.  Therefore, individual targets taking into account the case complexities should be used.
• Local protocols should be followed post-cardiac surgery and in cases of acute cerebral ischaemia/traumatic brain injury.

A red cell transfusion of 4ml/kg will produce an average rise in haemoglobin of ~10g/L, so a unit of packed red cells (250-300ml) should produce a 10g/L rise for a patient weighing 70-80kg. Patients who are not bleeding should be transfused a single unit and then reassessed before further blood is given. Haematology, oncology, gastrointestinal medicine (including liver disease) and renal medicine are the largest users of blood products.

Safe red cell transfusion

Provision of ABO compatible blood products is essential: transfusion of ABO incompatible red cells is almost universally fatal. The four ABO blood group types (A, B, AB and O) are identified based on the presence or absence of the A and B red cell antigens. Patients who lack an ABO antigen will produce the corresponding antibody. For example, patients who lack the A antigen (blood groups B and O) will produce an anti-A antibody.

Transfusion of products containing other red cell antigens (such as RhD or Kell) to patients with the corresponding antibody also presents a significant clinical risk. Unlike the A and B antigens, patients who lack RhD do not produce the antibody automatically, but can start to produce the antibody after exposure to foreign red cells.

To enable safe red cell selection for transfusion, a group and screen (G&S) should be performed. The G&S establishes the patient’s ABO and RhD blood group and identifies the presence of any atypical red cell antibodies in the patient’s plasma. If a historic G&S result is available, there are no issues with grouping the patient’s red cells and no atypical antibodies are identified, the patient may be appropriate for electronic issue of blood components. Otherwise, manual serological crossmatch is performed: donor red cells are combined with patient plasma using the indirect antiglobulin test (IAT) to check for evidence of a reaction.

For patients with haemoglobin disorders, the decision on whether to transfuse red cells is complex and requires input from a clinician with significant relevant expertise. The blood issued to sickle-cell patients should be negative for sickle haemoglobin and less than 14 days old; “fresher” blood may be associated with improved outcomes in this group of patients.  Up to 30% of patients on long-term transfusion support develop antibodies against red cell antigens, which reduces the probability of finding compatible red cells for future transfusions. In this group of patients, extended phenotyping should be carried out to allow the provision of more closely matched red cell transfusions (matched for ABO, full Rh and Kell antigens) which reduces the risk of forming red cell alloantibodies. Due to chronic haemolysis with increased red blood cell turnover in the morphologically abnormal sickle cells, it can be challenging to identify when a patient has developed a delayed haemolytic reaction during a sickle cell crisis. Making the diagnosis of a delayed haemolytic reaction is important as further transfusion can worsen the hyperhaemolysis.

Patients who require regular red cell transfusion support, for example those with myelodysplasia, are at risk of transfusional haemosiderosis and organ damage due to iron overload. In selected patients, iron chelation therapy with desferrioxamine is indicated. Iron chelation requires specialist monitoring.