Acute haemolytic reactions

When to suspect this adverse reaction

Characteristically begin with an increase in temperature and pulse rate.

Symptoms may include chills, rigours, tachycardia, dyspnoea, chest pain, flank/back pain, discomfort at infusion site, nausea, restlessness, a sense of dread/doom, hypotension, haematuria or abnormal bleeding, and may progress rapidly to shock.
 
Patients may develop oliguria, haemoglobinuria and haemoglobinaemia.
 
In anaesthetised patients, hypotension, haemoglobinuria and evidence of disseminated intravascular coagulation (DIC) may be the first sign of a reaction.

Usual causes

Acute haemolytic reactions can be both immune-mediated or non-immune-mediated. 
 
Immune-mediated reactions may be intra- or extravascular and associated with:

• ABO incompatibility between donor and recipient 
• red cell alloantibodies (non-ABO) in the recipient resulting from immunisation due to pregnancy or previous transfusion, and
• rare cases when a group A, B or AB recipient is transfused with platelets, plasma or an infusion of intravenous immunoglobulin (IVIg) containing high titre incompatible ABO antibodies, for example, anti-A given to an A or AB recipient, or anti-B given to a B or AB recipient. 

 
Transfused red cells are destroyed because of incompatibility between antigens on transfused donor red cells and an antibody in the recipient’s circulation. Alternatively, anti-A or anti-B in incompatible donor platelet, plasma, or in IVIg, may cause haemolysis of the recipient’s red cells.   

The severity and timing of reactions in relation to the transfusion depend on the specificity of red cell antigens, and the type (IgM or IgG) and titre of the causative antibody. 
 
The most severe reactions are associated with transfusion of ABO-incompatible red cells. Rapid destruction, possibly within 15 minutes, of as little as 10 mL of incompatible blood can cause symptoms of an acute haemolytic reaction. These reactions are typically due to clerical errors or patient identification errors such as improper labelling of samples, administering the wrong blood to the patient or testing errors.

Estimated incidence of acute haemolytic transfusion reactions 

* May be based on overseas data. 

Haemolysis may also occur in the presence of non-ABO red cell alloantibodies in the patient’s plasma which have not been previously identified.

Occasionally the patient may have an antibody at levels below the screening method's sensitivity. 

Rarely, reactions occur when uncrossmatched blood is given to an alloimmunised patient during an emergency transfusion.

Non-immune-mediated haemolysis can occur when red cells are physically or chemically damaged during storage or transfusion, and the haemolysed red cells are transfused. Causes include incorrect storage of red cells, thermal, osmotic or mechanical injury of red cells. For example, exposure to excess heat (incorrect use of a blood warmer), concomitant transfusion of red cells and infusion of hyperosmolar solutions, such as 5% dextrose, mechanical/physical damage, from transfusion through a small gauge needle and bacterially contaminated red cell units.
 

What to do

• Stop transfusion immediately and follow other steps for managing suspected transfusion reactions.
• Seek urgent medical assistance.
• Maintain renal output.
• Induce diuresis with intravenous fluids and diuretics.
• Support blood pressure and maintain an open airway as this may become a medical emergency. 

Do not restart the transfusion or administer additional blood components until cleared by a haematologist or Transfusion Service Provider.
 

Investigation

Clinically assess the patient for features of haemolysis.

Check clerical records, such as the ABO groups of the patient and transfused unit.
 
Perform a blood group, antibody screen and direct antiglobulin test (DAT) on both pre- and post-transfusion samples and serological crossmatch against the implicated unit/s.

Request a full blood count and film review, renal function (electrolytes, creatinine), and tests for haemolysis (e.g. LDH, bilirubin, haptoglobin, and urinalysis).  

In serious reactions a DIC work up may be helpful (aPTT, PT, fibrinogen, D-Dimer).

Updated June 2026