Reactions may occur days, months or even years after transfusion. Delayed reactions can be haemolytic or serological with no signs of hemolysis (Delaney et al. [59]). Usually the reaction is seen in a patient who has already made an alloantibody and the antibody has fallen to an undetectable level so that it is not detected on a pre‐transfusion antibody screen (Norfolk [202]). Re‐exposure to the antigen in a subsequent transfusion causes the antibody level to rise again, usually within 24 hours but sometimes up to 28 days after the transfusion (Delaney et al. [59]). The most frequent signs and symptoms in delayed reactions include dark urine, jaundice, fever, back pain, dyspnoea, chills and hypertension (Delaney et al. [59]). When a delayed reaction is suspected, further laboratory testing is required; however, the treatment is usually supportive and may require further transfusions to maintain the desired level of haemoglobin (Delaney et al. [59], Norfolk [202]).