Hematology / Oncology

Autoimmune Hemolytic Anemia

Introduction

Autoimmune Hemolytic Anemia (AIHA) is characterized by production of antibodies that bind to antigens on the erythrocyte surface. These antibodies then cause the destruction of RBCs thus shortening their life span.

If this destruction is at a high enough rate, and exceeds the bone marrow’s capacity to regenerate RBCs, the patient develops anemia and the associated signs and symptoms.

AIHA can be primary, where no evidence for a secondary causative disorder exists; or secondary in which hemolytic anemia is directly attributable to another systemic disease.

Epidemiology

AIHA is a relatively rare disorder in children and is most often seen after a recent viral illness. AIHA can be seen throughout childhood, but of note should prompt more attention when seen in teenagers as they are more likely to have an underlying systemic illness.  

While the precise incidence of the disease is not known, the number of affected children (<20 years old) are estimated to be less than 0.2/100,000 with the highest rates seen in pre-school age children.

Causes

AIHA can be idiopathic, post-infectious (EBV, mycoplasma), drug induced (penicillin, quinidine, a-methyldopa), or caused by chronic autoimmune disorders or an underlying malignancy.

Pathophysiology and Primary AIHA

In AIHA the hemolysis is mainly extravascular, with sequestration mainly occurring in the liver and the spleen. It most commonly involves IgG autoantibodies directed at RBC surface proteins  but can also be directed by IgM autoantibodies reacting with RBC polysaccharides.

The majority of cases are acute and carry a better prognosis with the possibility of spontaneous resolution within 6 months. The remaining cases are chronic and typically more difficult to treat. Chronic AIHA is found more commonly in the outlier age groups including kids less than 2 and teenagers. 

Primary AIHA includes warm reactive, cold reactive and paroxysmal cold hemoglobinuria. Secondary AIHA includes those resulting from systemic autoimmune diseases, malignancy and medications and are discussed below:

 

  • IgG mediated “warm reactive”
        
    • IgG autoantibodies or “warm reactive” antibodies are defined as such because their optimal antigen binding temperature sits conveniently close to normal body temperature at 37ºC. The extravascular hemolysis seen in AIHA occurs primarily when IgG-coated RBC are trapped by macrophages in the spleen. The RBCs are bound to macrophages via the macrophage receptors for the Fc fragment of the autoantibody.
    • The macrophages then proceed in destroying the “tagged” RBCs producing the typical hemolytic by-products which cause some of the clinically relevant signs such as dark urine and jaundiced skin. Interestingly as more RBCs are agglutinated by IgG, the major site of sequestration switches from the spleen to the liver, possibly due to the activation of complement.
    • Since IgG can actively bind RBCs at normal body temperature, hemolysis by macrophages is the predominant mechanism of destruction. IgG, however, is also capable of fixing complement which augments the hemolytic ability of the RBC autoantibodies.
    • In some cases (including the rare “cold reactive” IgG) complement will be detected while a DAT (see below) may be negative. If complement is present without IgG this is suggestive of a cold-reactive antibody that can fix complement at lower temperatures than are required for antibody binding.
                                                   
      • For any child in which this is found, IgG Donath-Landsteiner autoantibodies should be tested for. These autoantibodies are characteristic of paroxysmal cold hemoglobinuria and require special testing procedures that require the blood to be kept at 37ºC after collection.
            
  • IgM mediated “cold reactive”
         
    • IgM autoantibodies or “cold reactive” antibodies bind their antigens optimally at 0-4ºC but can adequately fix complement at normal body temperatures. IgM autoantibodies are often directed at i/I polysaccharide autoantigens on RBCs in contrast to the IgG predilection for RBC surface proteins.
    • The IgM autoantibodies that target i/I RBC polysaccharides most often develop in a post infectious state such as in response to a mycoplasma pneumonia infection (the I antigen) or EBV (the i antigen). In IgM mediated AIHA the liver is the primary clearance site for RBCs with bound IgM, clearing 80% of cells, while the spleen accounts for less than 20%.
    • Since IgM does not typically bind at normal body temperatures, RBC hemolysis is dependent entirely on compliment. In some cases a patient will be found to be “pan reactive” in that the patient’s autoantibodies are directed at a common RBC antigen, such as the Rh antigen, and will thus bind to foreign RBCs as well.
                   
      • This presents great difficulty for transfusion as the patient’s serum will be reactive with many donor blood samples, and can make finding compatible blood difficult to impossible.

Differential Diagnosis

The presentation of AIHA typically includes increased markers of inflammation (ESR, CRP) as well as evidence of RBC destruction including the presence of spherocytes on a smear and increased reticulocytes working to compensate for the hemolysis and resultant anemia.

The differential should include other causes of hemolysis, such as that found in non-immune hemolytic anemia including intrinsic red cell defects, hemolysis due to extrinsic factors (ie trugs or toxins) as well as mechanical damage hemolytic anemia as found in DIC and HUS. Based on the following findings different conditions should be considered and ruled out before making a diagnosis:

  • RBC abnormalities:
                                                     
    • Hereditary spherocytosis - Resembles AIHA because of presence of spherocytes and reticulcytosis, family history should be positive, DAT positive in AIHA, negative in hereditary spherocytosis.
    • Microangiopathic hemolytic anemia - most often present with schistocytes (RBC fragments) but may have spherocytes as well. These patients have concomitant thrombocytopenia and may have renal and abdominal symptoms (as in Hemolytic uremic syndrome from E. coli O157: H7 shiga-like toxin)  
  • Anemia:
       
    • Can be the result of excess losses (hemolysis or direct blood loss) or insufficient production (bone marrow failure or nutritional deficiencies/toxins). In the former, direct blood loss should be investigated in the case of a normocytic anemia, and testing should include occult blood testing to rule out chronic GI bleeds. In the latter conditions a low retic count would often be seen in comparison to the reticulocytosis found in AIHA and include transient red cell aplasia and acquired aplastic anemia (pancytopenia, may be associated with parvovirus B19).
    • Deficiencies in iron or lead poisoning can produce a microcytic anemia, while B12 and folate deficiencies produce a megaloblastic anemia and can be distinguished by peripheral smear.
    • Alpha and Beta-thalassemias as well as sickle cell anemia should also be ruled out.
        
  • Dark urine:
        
    • AIHA with an intravascular hemolytic component causes hemoglobin to be spilled into the urine (hemoglobinuria) but can easily be mistaken for bilirubin or simple highly concentrated urine. 
    • Intravascular hemolytic processes can include G6PD deficiency, several porphyrias, paroxysmal nocturnal hemoglobin or other non-immune causes of hemolytic anemia.
    • Myoglobinuria may not be distinguished from hemoglobinuria via urinalysis and is caused by rapid muscle breakdown as in rabdomyolysis.
         
  • Jaundice:
         
    • AIHA presents with elevated unconjugated bilirubin, but the presence of conjugated billirun prompt investigation into possible liver disease via blood levels of transaminases and coagfactors.
    • Further testing for suspected hepatic inflammation or dysfunction  should include hepatitis panels and CMV and EBV PCR tests.

Secondary AIHA

Recognizing secondary causes of AIHA are extremely important and often are seen in children with generalized immune system regulation irregularities. Secondary AIHA cases are typically categorized as “warm reactive” AIHA and when seen in children on either end of the age spectrum, less than 2 and teenagers, the possibility of an underlying systemic cause should be explored. Secondary AIHA is generally due to the following conditions:

  • Infection:  This relationship can be difficult to discern since most cases of AIHA are preceded by a non-specific viral illness. However, in cases where a specific pathogen can be identified, secondary AIHA should be considered. Important pathogens associated with AIHA include, mycoplasma pneumonia, EBV, measles, mumps, rubella and varicella and do so by triggering IgM antibodies with cross-reactivity for I/i RBC polysaccharides.
  • Autoimmune disease: Most common in older children and includes systemic lupus erythematous, sjogrens, juvenile rheumatoid arthritis, ulcerative colitis and hashimotos thyroiditis. Some children with congenital immunodeficiency disorders (CVID) or acquired (HIV) may also present with AIHA from the disruption of normal immune regulation and polyclonal B cell activation producing RBC autoantibodies.
  • Evans syndrome: Evan’s syndrome is seen when AIHA presents along with a second concomitant autoimmune cytopenia, most commonly thrombocytopenia and occasionally neutropenia. Children with Evans syndrome typically have a chronic course.
  • Cancer: AIHA can be seen in children with Hodgkin’s disease, acute leukemia, myelodysplasia or post allogenic bone marrow transplant. While the causative relationship is unknown it is postulated that an underlying immune deficiency or dysregulation may be the cause for both the malignancy and the AIHA.
  • Drugs: Rare but important cause of secondary AIHA caused by either exposure to drugs that trigger autoantibody production themselves or occasional drug binding with the RBC and promoting hemolysis.  Offending agents include: penicillins, cephalosporins, tetracycline, erythromycin, probenecid, acetaminophen and ibuprofen.

Signs and Symptoms

  • Pallor
  • Jaundice
  • Lethargy
  • Abdominal pain
  • Low-grade fever
  • Dark urine (sever hemolysis)
  • Hepatosplenomegaly

Diagnostic tests

  • CBC with smear
  • Normocytic, normochromic anemia
  • Reticulocytosis (or rare reticulocytopenia)
  • Spherocytes, schistocytes, poikilocytes, polychromasia
  • Normal WBC and Platelets (except in Evan’s syndrome)
  • +DAT (Direct Antigen Test/Coombs test) – patients RBCs are washed and combined with anti-globulin, agglutination signals a positive result
                                             
    • Gamma DAT: IgG attached to RBC
    • Nongamma DAT: C3 is attached, seen in IgM

   
Click on this link for a video explaination of the DAT/IAT:

Options for Treatment

  • 70-80% of patients who have AIHA present with acute symptoms and mild anemia and are more likely to have spontaneous remissions of the disease with resolution in 6 months, thus intervention may be minimal or unnecessary in these groups.
  • Patients that present with more chronic onset are more likely to have a relapsing and remitting course and will likely require treatment, however some can have spontaneous remissions in months or years. These patients are more likely to be very young or teenagers and should have secondary causes of the AIHA thoroughly investigated.
  • Transfusion is used in cases of life threatening illness. Patients need to be matched with donor blood carefully due to the presence of autoimmune RBC antibodies which may or may not be reactive with other donor blood. 
  • Exchange transfusion and plasmapheresis are even more effective in IgG mediated disease but are only temporary measures. In patient with “cold reactive” disease, blood should be transfused in at body temperature.
  • Steroids of 1-2 mg/kg dose have been shown to elicit responses in 80% of patients with “cold reactive” disease. In resistant patients, dosages can be increased to a maximum of 10mg/kg/ day doses for short bursts but must be rapidly decrease to a lower dose of 0.5-1.0 mg/kg. Unfortunately IgM mediated disease is typically non-responsive to steroids.
  • IVIG is effective for both solitary AIHA and in cases of multiple cytopenias such as in Evan’s syndrome. It can be administered in doses of 1-2 mg/kg/day over 1 to 2 days and works via competitive inhibition of the Fc receptors thus reducing uptake of Ig coated RBCs.
  • Splenectomy can be effective in disease processes where the majority of the hemolysis is in the spleen such as in IgG mediated AIHA. In IgM mediated hemolysis the liver is the main site of sequestration and spenectomy is not effective.
  • Warming: for patients with “cold agglutination” the patient should be kept warm at all times and should avoid exposures to cold environments and cold rooms, extra heat should be used in their hospital room and extra clothing beyond the typical hospital gown is a must to reduce body temperature drops.
  • Rituximab: anti-CD20 antibody can be used in cases of refractory primary or secondary AIHA. More research is needed in this area and use of Rituximab is currently an “off label use” and includes risk of profound agammaglobulinemias and cytopenias.

References

  1. Ware, Russel E., Donald H. Mahony, and Stephen A. Landlaw. "Autoimmune Hemolytic Anemia in Children." Up to Date (2012): n. pag. Web.
  2. Sackey, K. "Hemolytic Anemia: Part 1." Pediatrics in Review 20.5 (1999): 152-59. Print.
  3. Vaglio S, Arista MC, Perrone MP, et al. Autoimmune hemolytic anemia in childhood: serologic features in 100 cases. Transfusion 2007; 47:50.
  4. Schreiber AD, Frank MM. Role of antibody and complement in the immune clearance and destruction of erythrocytes. I. In vivo effects of IgG and IgM complement-fixing sites. J Clin Invest 1972; 51:575.
  5. Norton A, Roberts I. Management of Evans syndrome. Br J Haematol 2006; 132:125.