Fever HALO

Blood Transfusion Reactions Acronym

Author: Emily Miao, MD, PharmD
Editor: Alyssa Haag, MD
Editor: Lily Guo, MD
Editor: Kelsey LaFayette, DNP
Illustrator: Jannat Day
Modified: Jan 06, 2025

What is Fever HALO?

Fever HALO is an acronym that highlights the different types of adverse reactions that can occur following a blood transfusion with donated blood products or one of its components. However, with advances in donor screening, automation of health systems, and improved treatment strategies, the risks and incidence of transfusion reactions have continued to decrease.  

Symptoms of blood transfusion reactions can be non-specific and may differ in severity, ranging from mild to life-threatening or fatal. Regardless of the type of transfusion reaction, the first step in management is to stop the transfusion immediately, obtain vital signs, and assess the person's airway, breathing, and circulation. Timely recognition and management of blood transfusion reactions are important in improving patient care outcomes.  

An infographic detailing the blood transfusion reactions acronym Fever HALO.

What does “Fever” in Fever HALO mean?

Fever” in Fever HALO refers to the fever that is observed in a febrile non-hemolytic transfusion reaction. In this case, febrile refers to the presence of a low-grade fever, usually a temperature elevation of 1 to 2 degrees Fahrenheit (F). This reaction is also non-hemolytic in nature, meaning that hemolysis, or the destruction of red blood cells, does not occur. Febrile non-hemolytic transfusion reactions are thought to be caused by cytokines (i.e., an immunogenic protein released from the body’s cells) that accumulate in the blood products during storage. Symptoms include a low-grade fever, chills, headache, and flushing. A hemolysis work-up will be negative as the pathophysiology does not involve a hemolytic reaction. The treatment consists of supportive care measures to reduce symptoms (e.g., acetaminophen). The reaction should be documented and noted in the individual’s electronic medical record, and prophylactic strategies to reduce future risks may include leukoreduction (i.e., removal of white blood cells from cellular components) of blood products before transfusion. 

What does the “H” in Fever HALO mean?

The “H” in Fever HALO refers to hemolysis which occurs in acute or delayed hemolytic transfusion reactions. Hemolytic transfusion reactions occur due to ABO incompatibility, which occurs when donor blood is not compatible with the recipient’s blood, which can occur, for example, when a unit of blood is transfused to the wrong patient or blood is mislabeled during testing. The ABO group system determines the types of antigens (e.g., A, B, and O antigens) that are present in an individual’s red blood cells. For example, blood type A has A antigens on the red blood cell surface; blood type AB has A and B antigens on the red blood cell surface; and type O does not have any antigens present. If a person has blood type A, they produce antibodies to type B; if a person has blood type B, they produce antibodies to type A; and a person with type O blood has antibodies to both type A and B. Therefore, the compatibility of the donor and recipient’s blood types is crucial in preventing hemolytic transfusion reactions. For example, a hemolytic transfusion reaction can occur if a recipient with type A blood (i.e., red blood cells have A antigens, and thus the body produces antibodies to type B antigens) is transfused with donor type AB blood (i.e., red blood cells with type A and B antigens), destroying red blood cells.

More specifically, hemolytic transfusion reactions can be subcategorized into acute (i.e., within 15-20 minutes) and delayed (i.e., more than 24 hours and up to 3 days after transfusion). Acute hemolytic reactions may present with fevers, chills, hypotension, back or flank pain, kidney failure, bleeding, and disseminated intravascular coagulation (DIC) (i.e., a life-threatening condition that results in abnormal coagulation and systemic thrombosis). Treatment consists of immediately stopping the transfusion, supportive care with intravenous fluids, and monitoring urine output. Delayed hemolytic reactions similarly may present with fevers, anemia, jaundice, and malaise. Treatment is similar, consisting of stopping transfusion, providing supportive care with intravenous fluids, and monitoring for the development of life-threatening complications. 

What does the “A” in Fever HALO mean?

The “A” in Fever HALO refers to the allergy or allergic reaction that is observed in anaphylactic transfusion reactions. Anaphylaxis occurs in the recipient due to hypersensitivity or allergic reaction to one of the blood components. Anaphylaxis typically occurs due to an IgE-mediated hypersensitivity that occurs in recipients who lack IgA or haptoglobin (i.e., a protein produced by the liver). Anaphylactic transfusion reactions typically occur within minutes and may present with symptoms of acute hypotension, angioedema (i.e., swelling under the skin), urticaria, and wheezing. Treatment consists of intramuscular epinephrine, corticosteroids (e.g., methylprednisolone), and diphenhydramine, and support for airway, breathing, and circulation as needed. Repeated assessments of the airway, breathing, circulation and vital signs should be obtained to ensure hemodynamic stability. 

What does the “L” in Fever HALO mean?

The “L” in Fever HALO refers to lung or lung injury that occurs in transfusion-related acute lung injury (TRALI). TRALI is characterized by the acute onset of non-cardiogenic pulmonary edema or lung injury shortly (i.e., typically 1 to 6 hours) following transfusion. While many hypotheses have been proposed to explain TRALI, the most commonly held belief is that it occurs as a result of the passive transfer of specific antibodies (e.g., human leukocyte antigen or human neutrophil antigen antibodies) in the donor’s plasma which attacks the recipient’s leukocyte antigens. The treatment for TRALI consists of supportive care with oxygen delivery and repeated assessments of airway, breathing, circulation, and vital signs. Intubation may be necessary if the individual’s airway is compromised or if there is airway obstruction.  

What does the “O” in Fever HALO mean?

The “O” in Fever HALO refers to volume overload that occurs in transfusion-associated circulatory overload (TACO). TACO occurs when an individual receives a blood transfusion that is infused too quickly or too high in volume concerning their circulatory capacity. Individuals at high risk for TACO include the elderly and people with congestive heart failure, chronic kidney disease, or chronic anemia, as these comorbid conditions are predisposing factors for circulatory overload. Signs and symptoms typically occur within 1 to 6 hours and individuals typically will experience cardiogenic edema (i.e., increased fluid retention and swelling secondary to increased hydrostatic pressure in the capillaries). Signs of cardiogenic edema include shortness of breath, difficulty breathing, hypoxemia, elevated jugular venous pressure, and hypertension. An elevated serum brain natriuretic peptide (BNP) which suggests volume overload and chest X-ray demonstrating pulmonary interstitial edema is diagnostic for TACO. Treatment consists of supportive care measures such as supplemental oxygen delivery and intravenous diuretics to remove excess fluid from the body. To prevent future episodes of TACO, blood products can be infused at a slower rate.

What are the most important facts to know about the Fever HALO acronym?

Fever HALO is an acronym that highlights the different types of adverse reactions that can occur following a blood transfusion with donated blood products or one of its components. Symptoms of blood transfusion reactions can be non-specific and may differ in severity, ranging from mild to life-threatening or fatal. The different types of transfusion reactions include febrile non-hemolytic transfusions, acute or delayed hemolytic transfusion reactions, anaphylactic reactions, transfusion-related acute lung injury, and transfusion-associated circulatory overload. Regardless of the type of transfusion reaction, the first step in management is to stop the transfusion immediately, obtain vital signs, and assess the person's airway, breathing, and circulation.  

References


Carman M, Uhlenbrock JS, McClintock SM. CE: A review of current practice in transfusion therapy. Am J Nurs. 2018;118(5):36-44. doi:10.1097/01.NAJ.0000532808.81713.fc 


DeLisle J. Is this a blood transfusion reaction? Don't hesitate; Check it out. J Infus Nurs. 2018;41(1):43-51. doi:10.1097/NAN.0000000000000261  


Garraud O, Cognasse F, Laradi S, et al. How to mitigate the risk of inducing transfusion-associated adverse reactions. Transfus Clin Biol. 2018;25(4):262-268. doi:10.1016/j.tracli.2018.07.006 


Heddle NM. Pathophysiology of febrile nonhemolytic transfusion reactions. Curr Opin Hematol. 1999;6(6):420-426. doi:10.1097/00062752-199911000-00012 


McClosky ME, Cimino Brown D, Weinstein NM, et al. Prevalence of naturally occurring non-AB blood type incompatibilities in cats and influence of crossmatch on transfusion outcomes. J Vet Intern Med. 2018;32(6):1934-1942. doi:10.1111/jvim.15334  


Sirianni G, Perri G, Callum J, Gardner S, Berall A, Selby D. A retrospective chart review of transfusion practices in the palliative care unit setting. Am J Hosp Palliat Care. 2019;36(3):185-190. doi:10.1177/1049909118806456