Acute hemolytic transfusion reaction

An acute hemolytic transfusion reaction (AHTR) is a type of transfusion reaction that is associated with hemolysis. It occurs very soon after the transfusion, and within 24 hrs post-transfusion. It can occur quickly upon transfusing a few milliliters, or up to 1–2 hours post-transfusion.

It is also known as an "immediate hemolytic transfusion reaction". This is a medical emergency as it results from rapid destruction of the donor red blood cells by host antibodies (IgG, IgM). It is usually related to ABO blood group incompatibility - the most severe of which often involves group A red cells being given to a patient with group O type blood. Properdin then binds to complement C3 in the donor blood, facilitating the reaction through the alternate pathway cascade. The donor cells also become coated with IgG and are subsequently removed by macrophages in the reticuloendothelial system (RES). Jaundice and disseminated intravascular coagulation (DIC) may also occur. The most common cause is clerical error (i.e. the wrong unit of blood being given to the patient).

Acute hemolytic transfusion reactions are divided into two general types:

Early signs are fever, low blood pressure, anxiety, and red-colored urine.

Late signs are generalized bleeding, caused by disseminated intravascular coagulation, and low blood pressure.

Laboratory assessment is based on a positive Direct Antiglobulin Test (DAT), a decrease in serum haptoglobin, and an increase in blood levels of the enzyme lactate dehydrogenase and indirect bilirubin levels.

This may be caused by preformed IgM anti-A, anti-B or both. It may also be caused by other non-ABO IgG antibodies such as Rh, Kell, or Duffy. The former results in a severe intravascular hemolysis and the latter typically causes extravascular hemolysis. The reactions are mediated by cytokines like TNF, IL-8, monocyte chemoattractant protein, IL-1 etc.

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