Hemolytic Anemia


Primary Thrombotic Microangiopathy (see Thrombotic Microangiopathy)


Red Blood Cell (RBC) Membrane Defect

  • Cytoskeletal Membrane Defect
  • Lipid Membrane Disorders
  • Membrane Disorders Associated with Abnormalities of Erythrocyte Antigens
    • McLeod Syndrome
    • Rh Deficiency Syndromes
  • Membrane Disorders Associated with Abnormal Transport
    • Hereditary Xerocytosis

Red Blood Cell (RBC) Enzyme Defect

  • Glycolytic
    • Aldolase Deficiency
    • Diphosphoglycerate Mutase (DPGM) Deficiency
    • Glucose-6-Phosphate Isomerase (G6PI) Deficiency
    • Glyceraldehyde-3-Phosphate Dehydrogenase (GAPD) Deficiency
    • Hexokinase Deficiency
    • Phosphofructokinase (PFK) Deficiency
    • Phosphoglycerate Kinase (PGK) Deficiency
    • Pyruvate Kinase (PK) Deficiency
    • Triose Phosphate Isomerase (TPI) Deficiency
  • Redox
  • Nucleotide Metabolism
    • Adenylate Kinase Deficiency
    • Pyrimidine 5′-Nucleotidase Deficiency


  • Congenital Erythropoietic and Hepatoerythropoietic Porphyrias
  • Congenital Erythropoietic Protoporphyria


Autoimmune Hemolytic Anemia (AIHA)

Warm Autoimmune Hemolytic Anemia (48-70% of AIHA cases)

Cold Autoimmune Hemolytic Anemia

Mixed-Type Autoimmune Hemolytic Anemia

  • Idiopathic
  • Secondary

Drug-Induced Autoimmune Hemolytic Anemia

Other Antibody-Mediated Hemolytic Anemia

Chemical Injury to Red Blood Cell (RBC)

Hypersplenism (see Splenomegaly)

  • Physiology
    • Splenic Sequestration of One or More Cell Lines with Destruction, Resulting in Extravascular Hemolysis
  • Clinical

Mechanical Red Blood Cell (RBC) Destruction

Macroangiopathic Hemolytic Anemia

Microangiopathic Hemolytic Anemia (MAHA) + Thrombocytopenia

Primary Thrombotic Microangiopathy Syndrome (see Thrombotic Microangiopathy)
Disseminated Intravascular Coagulation (DIC) (see Disseminated Intravascular Coagulation])
  • Clinical: less severe than TTP usually
Giant Hemangioma (Kasabach-Merritt Syndrome) (see Kasabach-Merritt Syndrome)
Malignant Hypertension (see Hypertension)
Metastatic Carcinoma: due to activation of multifocal clotting -> hemolysis and thrombocytopenia
  • Associated Malignancies
    • Multiple Pulmonary Metastases from Adenocarcinoma
    • Multiple Pulmonary Metastases from Lymphoma (see Lymphoma)
  • Physiology: due to activation of multifocal clotting -> hemolysis and thrombocytopenia
Pregnancy-Related Disorders
Rheumatologic Disease
Transplant-Related Disease



  • Near Drowning (see Near Drowning)
    • Physiology: osmotic toxicity to RBC
  • Severe Hypophosphatemia (see Hypophosphatemia)
    • Physiology: impaired RBC glycolysis with impaired ATP formation -> spherocyte formation

Paroxysmal Nocturnal Hemoglobinuria (see Paroxysmal Nocturnal Hemoglobinuria)

  • Physiology: deficiency of the glycolipid, glycosylphosphatidyl-inositol (GPI), which anchors CD55 and CD59 to membrane -> increased complement-mediated RBC (and granulocyte/platelet) lysis

Physical Injury to Red Blood Cell

  • Heat/Burns (see Burns)
  • Hypotonic Solutions (IV): results in osmotic RBC lysis
  • Radiation (see Radiation Therapy)

Red Blood Cell Membrane (RBC) Defects

  • Cirrhosis/End-Stage Liver Disease (see Cirrhosis)
    • Physiologic Mechanisms Which Contribute to Hemolysis in Liver Disease
      • Acquired Alterations of Red Blood Cell Membrane
        • Burr Cells (Echinocytes)
        • Spur Cells (Acanthocytes)
        • Stomatocytes: mouth-shaped area of central pallor
        • Target Cells: due to decreased lecithin/cholesterol acyltransferase (LCAT) activity, resulting in increased cholesterol:phospholipid ratio -> absolute increase in surface area of the red blood cell membrane
      • Hypersplenism (see Splenomegaly): due to portal hypertension
  • Acquired Acanthocytosis
  • Acquired Stomatocytosis
  • Spur Cell Hemolysis


Background-Iron Physiology

  • Iron: free iron is toxic to cells and is therefore stored in alternate forms
    • Within Cells: iron is complexed to protein, as ferritin or hemosiderin (apoferritin binds to free ferrous iron and stores it in its ferric state)
      • As ferritin accumulates with cells of the reticuloendothelial system, protein aggregates are formed as hemosiderin -> hemosiderin is less readily available for utilization than ferritin is
    • In the Circulation: serum iron is bound to transferrin

Background-Red Blood Cell Physiology

  • Normal Red Blood Cell Lifespan: 110-120 days
    • Definition of Hemolysis: shortening of RBC survival to <100 days
    • Normal Rate of Red Blood Cell Age-Independent Random Hemolysis: rate is <0.05-0.5% per day
  • Hemolysis (Anemia) Results in a Compensatory increase in the Erythropoietin Secretion: increases reticulocyte percentage (and absolute reticulocyte count) -> increases RBC production
    • Reticulocytosis is Found in Most Patients with Hemolytic Anemia (and Acute Hemorrhage)

Predominant Site of Hemolysis

Intravascular Hemolysis (RBC Destruction Within the Vascular Space)

  • General Comments
    • Intravascular Hemolysis Results in Release of Hemoglobin into the Plasma Either as Red Oxyhemoglobin or Brownish Oxidized Methemoglobin: plasma has a red-brown color
      • Free hemoglobin binds to haptoglobin -> hemoglobin-haptoglobin complex is rapidly removed by the liver (results in decreased serum haptoglobin level)
      • Lysed hemoglobin breaks down into alpha-beta dimers, which are small (MW: 34k) and cleared via glomerular filtration by the kidney -> resulting in hemoglobinuria
      • Hemoglobin dimers filtered by the kidney are taken up by renal tubular cells, degraded, and the iron stored as hemosiderin -> when renal tubular cells are later sloughed into the urine (approximately 7 days later), hemosiderinuria can be detected (by the Prussian blue reaction)
  • Autoimmune Hemolytic Anemia (AIHA): may occur in some cases (where IgM forms an antibody-antigen complex on the RBC membrane -> activation of complement with RBC lysis)
    • Cold Agglutinin Syndrome: some cases
  • Favism (see Favism): usually intravascular
  • Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency (see Glucose-6-Phosphate Dehydrogenase Deficiency): at least partly intravascular
  • Hypotonic Solutions (IV): results in osmotic RBC lysis
  • Infection
  • March Hemoglobinuria: usually intravascular
  • Microangiopathic Hemolytic Anemias (MAHA): usually intravascular
  • Paroxysmal Cold Hemoglobinuria (PCH) (see Paroxysmal Cold Hemoglobinuria): usually intravascular
  • Paroxysmal Nocturnal Hemoglobinuria (PNH) (see Paroxysmal Nocturnal Hemoglobinuria): usually intravascular
  • Rho(D) Immunoglobulin (IV)
  • Sepsis (see Sepsis)
  • Transfusion Reaction
  • Toxins

Extravascular Hemolysis (Red Blood Cell Destruction in the Spleen, Other Reticuloendothelial Tissues, or Extravasated Blood/Hematoma)

  • General Comments
    • Hepatic Destruction of RBC’s: primary site of destruction of severely damaged RBC’s (especially those coated with complement)
      • Liver receives larger percentage of cardiac output than the spleen
    • Splenic Destruction of RBC’s: primary site of destruction of poorly-deformable RBC’s (spherocytes, etc), due to narrow passage in the cords of Billroth -> macrophage ingestion of RBC’s (with degradation of hemoglobin to iron/biliverdin/carbon monoxide)
      • Biliverdin is converted to unconjugated bilirubin, which is released into the plasma
  • Autoimmune Hemolytic Anemia (AIHA): usually extravascular (most cases are IgG-mediated)
    • Warm Autoimmune Hemolytic Anemia
    • Cold Autoimmune Hemolytic Anemia
    • Drug-Induced Autoimmune Hemolytic Anemia
  • Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency (see Glucose-6-Phosphate Dehydrogenase Deficiency): at least partly intravascular
  • Hereditary Elliptocytosis (see Hereditary Elliptocytosis)
  • Hereditary Spherocytosis (see Hereditary Spherocytosis)
  • Hypersplenism (see Splenomegaly): splenic sequestration in sickle cell disease
  • Infection
  • Intravenous Immunoglobulin (IVIG) (see Intravenous Immunoglobulin)
  • Large Granular Lymphocyte Leukemia
  • Oxidants
  • Pyruvate Kinase (PK) Deficiency
  • Sickle Cell Disease (see Sickle Cell Disease)
  • Thalassemias (see Thalassemias): alpha/beta-types
  • Toxins
    • Copper (see Copper)
    • Lead (see Lead)
    • Snake Bites
    • Spider Bites
  • Unstable Hemoglobins


Complete Blood Count (CBC) (see Complete Blood Count)

  • MCV and MCH: usually increased in hemolysis (reticulocytes are larger than mature RBC’s)
  • Red Cell Distribution Width (RDW): reflects anisocytosis

Serum Lactate Dehydrogenase (LDH) (see Serum Lactate Dehydrogenase)

  • Etiology of Increased LDH
    • Hemolytic Anemia: may be increased up to 10x normal with intravascular hemoylsis
      • Although LDH is sensitive for hemolysis, it is not specific (can be seen released from neoplastic cells, liver, lung, etc)

Serum Haptoglobin (see Serum Haptoglobin)

  • Etiology of Decreased Serum Haptoglobin
    • Hemolytic Anemia: decrease in haptoglobin is more likely in intravascular hemolysis than in extravascular hemolysis
      • However, haptoglobin is an acute phase reactant -> can increase in infections and in other reactive states

Indirect Hyperbilirubinemia (see Hyperbilirubinemia)

  • Etiology of Unconjugated (Indirect) Bilirubinemia
    • Hemolytic Anemia: but this is not specific, as it can also occur in Gilbert’s disease
      • In hemolysis, indirect bilirubin is usually <3 mg/dL (higher levels of indirect bilirubinemia indicate the presence of liver disease)

Urinalysis (see Urinalysis)

  • Urine Bilirubin (see Urine Bilirubin)
    • Physiology: the kidneys do not filter unconjugated bilirubin (as it is avidly bound to albumin) -> therefore, the presence of bilirubinuria indicates the presence of conjugated bilirubinemia
    • Etiology of Bilirubinuria*
  • Urobilinogen
    • Etiology of Increased Urobilinogen: in urine and stool
      • Hemolytic Anemia

Urine Hemoglobin (Hemoglobinuria) + Urine Hemosiderin (Hemosiderinuria) (see Hemoglobinuria and Hemosiderinuria)

  • Physiology: with intravascular hemolysis, hemoglobin is released from hemolyzed RBC’s into the blood, exceeding the binding capacity of haptoglobin -> excess hemoglobin is filtered by the kidney
    • Some of this hemoglobin is excreted in the urine, resulting in hemoglobinuria (with “coca cola-colored” urine)
    • Some of this hemoglobin is reabsorbed in the proximal convoluted tubule, where the iron portion is removed and stored in ferritin or hemosiderin -> proximal tubule cells slough off (containing the hemosiderin) and are excreted into the urine, resulting in hemosiderinuria
      • Urine hemosiderin (composed of a complex of ferritin, denatured ferritin, and other material) can be detected in iron-stained urinary sediment (within the sloughed proximal tubular cells)
  • Diagnostic Utility
    • Urine hemoglobin disappears more quickly from the urine than hemosiderin, making it less sensitive for the presence of hemolysis (especially in cases with intermittent hemolysis)
    • Urine Hemosiderin can remain in the urine for several weeks (making it a more sensitive marker for hemolysis in the recent past): however, after an acute episode of intravascular hemolysis, several days may pass before urinary hemosiderin can be detected

Reticulocyte Count (see Reticulocyte Count)

  • Reticulocytes are Newly-Released RBC’s: they are slightly larger than mature RBC’s and have some residual ribosomal RNA -> presence of RNA allows for staining, with detection and counting
  • Normal Reticulocyte Percentage: 1-2%
  • Reticulocyte Production Index (RPI) = Reticulocyte Percentage x (Patient’s Hct/Normal Hct) x (1/RMT): corrects reticulocyte percentage for the degree of anemia (normalized to Hct 45%) and reticulocyte maturation time (RMT)
    • Use Normal Hct = 45%
    • RMT
      • Hct 45% -> RMT = 1.0 days
      • Hct 15% -> RMT = 2.5 days
    • Reticulocyte Production Index > or = to 2.5%: indicates adequate bone marrow response to anemia [MEDLINE]
      • Acute/Subacute Hemorrhage: note that acute hemorrhage may not result in an increased RPI, due to the time that it takes to increase epo synthesis and increase bone marrow RBC production
      • Hemolytic Anemia
    • Reticulocyte Production Index <2.5%: indicates inadequate bone marrow response to anemia [MEDLINE]
      • Chronic Anemia
      • Hypoproliferative Anemia: such as iron deficiency, marrow hyporesponsiveness, aplasia, etc
      • Maturation Disorder: such as vitamin B2 deficiency, etc

Direct Coombs Test (Direct Anti-Globulin Test) (see Direct Coombs Test)

  • Usually Positive in Immune Hemolytic Anemias: however, about 5-10% of autoimmune hemolytic anemia cases are direct Coombs-negative
    • Polybrene Test: can be used to diagnose direct Coombs-negative autoimmune hemolytic anemia

Iron Studies

  • Iron (see Serum Iron): serum iron level represents the amount of circulating iron that is bound to transferrin (although this level varies diurnally)
    • Normal Serum Iron: 50-150 ug/dL
  • Total Iron Binding Capacity (TIBC): indirect measure of the amount of circulating transferrin (which is the transport protein for iron)
    • Normal TIBC: 300-360 ug/dL
    • TIBC (in μg/dL) = Transferrin Concentration (in mg/dL) x 1.389
  • Transferrin Saturation (Iron/TIBC ratio x 100)
    • Normal Transferrin Saturation: 15-45%
    • Transferrin Saturation <15%: indicates iron deficiency
    • Transferrin Saturation 45-100%: indicates iron overload
  • Serum Ferritin (see Serum Ferritin): represents the total body iron store
    • Normal Serum Ferritin (Female): 20-200 ug/L -> average 100 ug/L
    • Normal Serum Ferritin (Male): 20-300 ug/L -> average 30 ug/L
    • Serum Ferritin <12: indicates iron deficiency
    • Serum Ferritin 300-4000: indicates iron overload
  • Iron Studies in Various Disease States

Serum Vitamin B12 Level (see Serum Vitamin B12)

  • Decreased in Vitamin B12 Deficiency

Serum Folate Level (see Serum Folate)

  • Decreased in Folate Deficiency, Which May Occur in the Setting of Chronic Hemolysis

Peripheral Blood Smear (see Peripheral Blood Smear)


  • Definition: elliptical RBC’s
  • Etiology
    • Hemolytic Anemia

Leukoerythroblastic Smear

  • Definition: smear with precursor cells of the myeloid and erythroid lineage, which usually indicates the presence of extramedullary hematopoiesis (predominantly in the spleen)
  • Etiology
    • Bone Marrow Infiltration (see Pancytopenia)
    • Myelofibrosis/Myelophthisis (see Pancytopenia)
    • Severe Stress
      • Blood Loss
      • Hemolysis
      • Infection
  • Features
    • Anisocytosis: RBC’s are of different sizes
    • Immature Myeloid Cells
    • Immature Nucleated RBC’s
    • Megakaryocytic Fragments
    • Poikilocytosis: abnormally-shaped RBC’s
    • Polychromasia (Polychromatophilia): large number of grayish-blue RBC’s, indicative of RBC immaturity
    • Teardrop-Shaped RBC’s (Dacrocytes)

Schistocytes/Helmet Cells

  • Definition: fragmented RBC’s
  • Etiology

Spur Cells (Acanthocytes)

  • Definition
  • Etiology
    • Spur Cell Anemia

Target Cells (Bell-Shaped Codocytes, Mexican Hat Cells)

  • Definition
  • Etiology
    • Asplenia (see Asplenia): splenic macrophages normally clear opsonized, deformed, and damaged red blood cells -> if splenic macrophage function is abnormal/absent because due to splenectomy, altered red blood cells will not be removed from the circulation appropriately
      • Auto-Splenectomy Resulting from Sickle Cell Disease (see Sickle Cell Disease)
      • Post-Splenectomy
    • End-Stage Liver Disease (ESLD) (see End-Stage Liver Disease): decreased lecithin/cholesterol acyltransferase (LCAT) activity, resulting in increased cholesterol:phospholipid ratio -> absolute increase in surface area of the red blood cell membrane
    • Hemoglobin C Disease
    • Iron Deficiency Anemia (see Iron Deficiency Anemia): decrease in hemoglobin content relative to red blood cell surface area
    • Thalassemias (see Thalassemias): decreased hemoglobin content relative to red blood cell surface area


  • Definition: presence of spherocytes indicates loss of RBC membrane surface area in excess of loss of cell volume -> spherocytes are a feature of many hemolytic anemias
  • Etiology
    • Interaction of Membrane-Antibody Complex with Reticuloendothelial System
      • Autoimmune Hemolytic Anemia (AIHA)
      • Alloimmune Hemolytic Anemia: ABO incompatibility
    • Microangiopathic Hemolytic Anemias (MAHA)
    • Oxidant Injury
    • Phospholipases or Other Membrane Active Enzymes
    • Othe

Clinical Differentiation of Hemolytic Syndromes

Clinical Differentiation of Intravascular Hemolysis Syndromes


Clinical Manifestations

Hematologic Manifestations

Gastrointestinal/Hepatic Manifestations

Rheumatologic/Orthopedic Manifestations

  • Skull/Skeletal Deformities: can occur in childhood due to increased hematopoiesis and resultant bone marrow expansion in disorders such as thalassemia

Pulmonary Manifestations