Microangiopathic hemolytic anemia is intravascular hemolysis caused by excessive shear or turbulence in the circulation. Excessive shear or turbulence in the circulation causes trauma to red blood cells (RBCs) in the peripheral blood, leading to fragmented RBCs (eg, triangles, helmet shapes) called schistocytes (see
photo ).
Schistocytes in the peripheral smear are diagnostic. Schistocytes cause high RBC distribution width, reflecting the anisocytosis. Microangiopathic hemolytic anemia encompasses RBC fragmentation caused by microvascular injury as well as by mechanical devices. Causes of fragmentation hemolysis include Stenotic or mechanical heart valves, or prosthetic valve dysfunction (ie,
perivalvular leak) Rare cases of significant repetitive impact, such as foot strike hemolysis (march hemoglobinuria), karate strikes, swimming, or hand drumming Click here for Patient Education  Copyright © 2022 Merck & Co., Inc., Rahway, NJ, USA and its affiliates. All rights reserved. Practice EssentialsHemolysis is the premature destruction of erythrocytes. A hemolytic anemia will develop if bone marrow activity cannot compensate for the erythrocyte loss. The severity of the anemia depends on whether the onset of hemolysis is gradual or abrupt and on the extent of erythrocyte destruction. Mild hemolysis can be asymptomatic while the anemia in severe hemolysis can be life threatening and cause angina and cardiopulmonary decompensation. The clinical presentation also reflects the underlying cause for hemolysis. For example, sickle cell anemia (see the image below) is associated with painful occlusive crises. (See Presentation.) Hemolytic anemia has multiple causes, and the clinical presentation can differ depending on the etiology. An array of laboratory tests are available for detecting hemolysis, and specialized tests may be indicated to diagnose the cause for hemolysis (see Workup). There are differences in the management of various types of hemolytic anemias (see Treatment). Go to Anemia, Iron Deficiency Anemia, and Chronic Anemia for complete information on these topics. PathophysiologyHemolysis can be due to hereditary and acquired disorders. [1, 2] The etiology of premature erythrocyte destruction is diverse and can be due to conditions such as intrinsic membrane defects, abnormal hemoglobins, erythrocyte enzymatic defects, immune destruction of erythrocytes, mechanical injury, and hypersplenism. Hemolysis may be an extravascular or an intravascular phenomenon. Autoimmune hemolytic anemia and hereditary spherocytosis are examples of extravascular hemolysis because the red blood cells are destroyed in the spleen and other reticuloendothelial tissues. [3] Intravascular hemolysis occurs in hemolytic anemia due to the following:
Hemolysis may also be intramedullary, when fragile red blood cell (RBC) precursors are destroyed in the bone marrow prior to release into the circulation. Intramedullary hemolysis occurs in pernicious anemia and thalassemia major. Hemolysis is associated with a release of RBC lactate dehydrogenase (LDH). Hemoglobin released from damaged RBCs leads to an increase in indirect bilirubin and urobilinogen levels. A patient with mild hemolysis may have normal hemoglobin levels if increased RBC production matches the rate of RBC destruction. However, patients with mild hemolysis may develop marked anemia if their bone marrow erythrocyte production is transiently shut off by viral (parvovirus B-19) or other infections. This scenario would be an aplastic crisis since the bone marrow can no longer compensate for ongoing hemolysis. Skull and skeletal deformities can occur in childhood due to a marked increase in hematopoiesis and resultant bone marrow expansion in disorders such as thalassemia. EtiologyA wide range of causes of hemolytic anemia have been documented. [7, 8, 9, 10, 11, 12, 13, 14, 15, 1, 16] Only the more commonly encountered hemolytic disorders are discussed in this article. Recent articles have noted that intravenous immunoglobulin G (IVIG) therapy given during pregnancy, [17] the contrast medium iomeprol, [18] and mitral valve replacement [19] can cause hemolysis. Hereditary disorders may cause hemolysis as a result of erythrocyte membrane abnormalities, enzymatic defects, and hemoglobin abnormalities. Hereditary disorders include the following: Acquired causes of hemolysis include the following:
Autoimmune hemolytic anemia (AIHA) can be due to warm or cold autoantibody types and, rarely, mixed types. [16, 24, 25, 26] Most warm autoantibodies belong to the immunoglobulin IgG class. These antibodies can be detected by a direct Coombs test, which also is known as a direct antiglobulin test (DAT). AIHA may occur after allogeneic hematopoietic stem cell transplantation. The 3-year cumulative incidence in this population has been reported at 4.44%. [27] AIHA is rare in children and has a range of causes. Autoimmune hemolysis can be primary or secondary to conditions such as infections (viral, bacterial, and atypical), systemic lupus erythematosus (SLE), autoimmune hepatitis (AIH), and H1N1 influenza. H1N1 influenza–associated AIHA in children may respond to treatment with oseltamivir and intravenous immunoglobulin. [9] Fetal splenomegaly and associated hepatomegaly could be due to hemolysis, but infections are the most likely cause. Congestive heart failure and metabolic disorders should be considered. Rarely, leukemia, lymphoma, and histiocytosis are associated with splenomegaly. [28] Microangiopathic hemolytic anemia, which results in the production of fragmented erythrocytes (schistocytes), may be caused by any of the following [29, 30] :
In paroxysmal nocturnal hemoglobinuria, hemolysis is due to intravascular complement-mediated destruction of erythrocytes. EpidemiologyHemolytic anemia represents approximately 5% of all anemias. Acute AIHA is relatively rare, with an incidence of one to three cases per 100,000 population per year. [31] A review of the Nationwide Inpatient Sample database found that the prevalence of nonimmune hemolytic anemia was 0.17% in all hospitalized patients with alcoholic liver disease. The presence of anemia among inpatients with alcoholic liver disease was associated with a significantly worse prognosis, including longer average length of stay (8.8 vs. 6.0 d1), increased hospital charges ($38,961 vs. $25,244), and higher mortality (9.0% vs. 5.6%). [32] Hemolytic anemias are not specific to any race. However, sickle cell disorders are found primarily in Africans, African Americans, some Arabic peoples, and Aborigines in southern India. Several variants of G6PD deficiency exist. The A(-) variant is found in West Africans and African Americans. Approximately 10% of African Americans carry at least 1 copy of the gene for this variant. The Mediterranean variant occurs in individuals of Mediterranean descent and in some Asians. Most cases of hemolytic anemia are not sex specific. However, AIHA is slightly more likely to occur in females than in males. G6PD deficiency is an X-linked recessive disorder and therefore more males are affected while more females are carriers. Although hemolytic anemia can occur in persons of any age, hereditary disorders are usually evident early in life. AIHA is more likely to occur in middle-aged and older individuals. PrognosisThe prognosis for patients with hemolytic anemia depends on the underlying cause. Overall, mortality rates are low in hemolytic anemias. However, the risk is greater in older patients and patients with cardiovascular impairment. Morbidity depends on the etiology of the hemolysis and the underlying disorder, such as sickle cell anemia or malaria. Patient EducationPatients should be able to identify symptoms and signs of the recurrence of hemolysis. They should seek prompt medical attention if symptoms reoccur. Patients with G6PD deficiency should know which medications to avoid. For patient education information, see Anemia.
Author Srikanth Nagalla, MD, MS, FACP Chief of Benign Hematology, Miami Cancer Institute, Baptist Health South Florida; Clinical Professor of Medicine, Florida International University, Herbert Wertheim College of Medicine Srikanth Nagalla, MD, MS, FACP is a member of the following medical societies: American Society of Hematology, Association of Specialty Professors Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Alexion; Alnylam; Kedrion; Sanofi; Dova<br/>Serve(d) as a speaker or a member of a speakers bureau for: Dova; Sanofi. Coauthor(s) Specialty Editor Board Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference Disclosure: Received salary from Medscape for employment. for: Medscape. Ronald A Sacher, MD, FRCPC, DTM&H Professor Emeritus of Internal Medicine and Hematology/Oncology, Emeritus Director, Hoxworth Blood Center, University of Cincinnati Academic Health Center Ronald A Sacher, MD, FRCPC, DTM&H is a member of the following medical societies: American Association for the Advancement of Science, American Association of Blood Banks, American Clinical and Climatological Association, American Society for Clinical Pathology, American Society of Hematology, College of American Pathologists, International Society of Blood Transfusion, International Society on Thrombosis and Haemostasis, Royal College of Physicians and Surgeons of Canada Disclosure: Nothing to disclose. Chief Editor Emmanuel C Besa, MD Professor Emeritus, Department of Medicine, Division of Hematologic Malignancies and Hematopoietic Stem Cell Transplantation, Kimmel Cancer Center, Jefferson Medical College of Thomas Jefferson University Emmanuel C Besa, MD is a member of the following medical societies: American Association for Cancer Education, American Society of Clinical Oncology, American College of Clinical Pharmacology, American Federation for Medical Research, American Society of Hematology, New York Academy of Sciences Disclosure: Nothing to disclose. Additional Contributors Paul Schick, MD † Emeritus Professor, Department of Internal Medicine, Jefferson Medical College of Thomas Jefferson University; Research Professor, Department of Internal Medicine, Drexel University College of Medicine; Adjunct Professor of Medicine, Lankenau Hospital Paul Schick, MD is a member of the following medical societies: American College of Physicians, American Society of Hematology Disclosure: Nothing to disclose. What are the Microangiopathic hemolytic anemias?Microangiopathic hemolytic anemia (MAHA) — MAHA is a descriptive term for non-immune hemolysis (ie, Coombs-negative hemolysis) resulting from intravascular red blood cell fragmentation that produces schistocytes on the peripheral blood smear (picture 1) [1].
How is Microangiopathic hemolytic anemia diagnosed?Diagnostic criteria and tests
Clinicopathologic features of hemolysis (as described in Clinical Features section) A negative Coombs test (also called a direct antiglobulin test) Schistocytes on microscopic examination of the peripheral blood smear (usually more than two per high power field [100x]) Thrombocytopenia.
What causes Microangiopathic hemolysis?Microangiopathic hemolytic anemia is intravascular hemolysis caused by excessive shear or turbulence in the circulation.
What is the pathogenesis of Microangiopathic hemolytic anemia?"Microangiopathic hemolytic anemia (MAHA)" is now used to designate any hemolytic anemia related to RBC fragmentation, occurring in association with small vessel disease. In DIC, RBC fragmentation is thought to result from the deposition of fibrin or platelets within the microvasculature.
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Which one of the following is a feature found in all microangiopathic hemolytic anemias
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