Comprehensive Notes on Hemolytic Anemias

Extrinsic Hemolytic Anemia

  • Anemia caused by external factors that damage RBCs or hasten their destruction; RBC structure/function are otherwise normal.
  • Two broad categories:
    • Nonimmune hemolytic anemia
    • Immune hemolytic anemia
  • Diagnostic clue on peripheral smear (PB): RBC morphological changes may include schistocytes, spherocytes, or intracellular organisms.
  • Key sources: Rodak’s Hematology Clinical Principles and Applications; Chapter 22.

Nonimmune Hemolytic Anemia

  • External insults lead to premature RBC destruction (extrinsic defects).
  • Subcategories/features:
    • Mechanical/physical damage
    • Microangiopathic hemolytic anemia (MAHA): damage to microvasculature
    • Macroangiopathic hemolytic anemia: damage to large vessels and heart (e.g., prosthetic valves)
    • Infections (e.g., malaria)
    • Chemical/drug/venom/burn injuries
  • MAHA is a prominent nonimmune mechanism and is covered in more detail below.

Immune Hemolytic Anemia

  • RBC destruction mediated by antibodies, complement, or both.
  • Peripheral smear clues may include schistocytes, spherocytes, or intracellular organisms depending on mechanism.
  • Direct evidence is via DAT (direct antiglobulin test) showing in vivo sensitization of RBCs by IgG, C3b, or C3d (see DAT section).

Microangiopathic Hemolytic Anemia (MAHA)

  • Defined by intravascular RBC fragmentation and consumption of platelets leading to thrombocytopenia.
  • Typical laboratory pattern mirrors hemolysis: decreased Hb, elevated LDH, indirect bilirubin, decreased haptoglobin; schistocytes on smear.
  • Often accompanied by thrombocytopenia due to platelet consumption in microvascular thrombi.
  • Conditions commonly grouped under MAHA include:
    • Thrombotic Thrombocytopenic Purpura (TTP)
    • Hemolytic Uremic Syndrome (HUS)
    • HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets)
  • HELLP is a pregnancy-associated MAHA variant.

Hemolytic Uremic Syndrome (HUS)

  • Classic MAHA with thrombocytopenia and acute renal failure due to endothelial damage in glomerular microvasculature.
  • Typical HUS: caused by bacteria producing Shiga toxin; commonly preceded by gastroenteritis with bloody diarrhea; accounts for about
    ext{≈} 90 ext{ extasciitilde{} of cases}
  • Atypical HUS: due to unregulated activation of the alternative complement pathway.
  • Lab findings: MAHA pattern; renal involvement prominent.
  • Differential: HUS vs TTP; both are life-threatening and require rapid treatment.

Thrombotic Thrombocytopenic Purpura (TTP)

  • Rare, life-threatening MAHA with abrupt onset of MAHA, severe thrombocytopenia, and markedly elevated serum LD.
  • Etiology:
    • Deficiency of ADAMTS13 – von Willebrand factor-cleaving protease; insufficient cleavage leads to unusually large VWF multimers and platelet aggregation.
    • Idiopathic: autoantibodies to ADAMTS13 causing severe deficiency.
    • Secondary: triggered by infections, pregnancy, trauma, inflammation, etc., which can suppress ADAMTS13 synthesis.
    • Inherited form: Upshaw-Schulman syndrome (ADAMTS13 gene mutations).

Box 22.2 Laboratory Findings in TTP and HUS

  • Hematologic: Decreased Hb; decreased platelets; increased reticulocyte count.
  • Peripheral blood film: Schistocytes; polychromasia; NRBCs (severe cases).
  • Biochemical: Markedly increased LD; increased total and indirect bilirubin; decreased haptoglobin; hemoglobinemia; hemoglobinuria; proteinuria, hematuria, and casts.
  • Clinical context: due to systemic ischemia and hemolysis; more characteristic in TTP.

HELLP Syndrome

  • Severe complication of pregnancy with triad: hemolysis, elevated liver enzymes, and low platelets.
  • Occurs in ext{≈} 10 ext{-}20 ext{ extasciitilde{}} ext{of pregnancies with severe preeclampsia/eclampsia}
  • Diagnostic features: markedly elevated AST/ALT, low platelets, elevated LDH.
  • Major diagnostic criterion includes the combination of liver enzyme elevation and thrombocytopenia.
  • Distinguishing feature: normal PT and aPTT help differentiate HELLP from disseminated intravascular coagulation (DIC).

Disseminated Intravascular Coagulation (DIC)

  • Widespread activation of coagulation leading to clot formation and subsequent bleeding due to platelet consumption.
  • Can complicate many disorders from severe infections to metastatic cancers.
  • MAHA-like features with coagulation abnormalities: PT and aPTT prolonged; fibrinogen decreased; D-dimer increased.

Macroangiopathic Hemolytic Anemia

  • Traumatic Cardiac Hemolytic Anemia (mechanical hemolysis from prosthetic heart valves).
  • Features:
    • Mild anemia; schistocytes are the main morphological finding.
    • Reticulocytosis with a normal platelet count.
    • Hemolysis depends on severity and marrow compensation.
    • Management often involves repair or replacement of the prosthesis.

Exercise-Induced Hemoglobinuria

  • Exercise-induced hemolysis seen in long-distance runners, cyclists, swimmers, and hand drummers.

Malaria and Babesiosis: RBC Injury by Infectious Agents

Malaria

  • Caused by RBC infection with Plasmodium species: P. extit{falciparum}, P. extit{vivax}, P. extit{ovale}, P. extit{malariae}, P. extit{knowlesi}.
  • Pathogenesis highlights:
    • Four clinical outcomes after mosquito bite: No infection, asymptomatic parasitemia, uncomplicated malaria, severe malaria.
    • Outcomes depend on parasite factors (species, inoculum, replication rate, virulence, drug resistance), host factors (age, pregnancy, immune status, prior exposure, genetics), and geographic/social factors (endemicity, poverty, treatment availability).
    • Immunity: most people in high-transmission areas develop some immunity; young children and first pregnancies are high-risk for severe malaria.
    • Severe malaria is mainly due to falciparum; vivax and knowlesi can also cause severe disease; P. malariae and P. ovale are usually uncomplicated.
  • Major complications of severe malaria: respiratory distress syndrome, circulatory shock, liver and kidney failure, hypoglycemia, severe anemia, metabolic acidosis.
  • Mechanisms of anemia:
    • Direct lysis of RBCs by parasites
    • Immune destruction of infected and non-infected RBCs (often in spleen)
    • Inhibition of erythropoiesis and ineffective erythropoiesis
  • Parasite proteins shed into RBC membranes can bind both infected and non-infected cells, altering membranes to promote Ig and complement binding and clearance in the spleen.
  • Hemozoin (parasite pigment) triggers inflammatory cytokines (TNF-α, IFN-γ), inhibiting erythropoiesis; IL-6 increases hepcidin, reducing iron availability for developing RBCs.
  • Invasion specifics by species:
    • P. vivax and P. ovale infect reticulocytes.
    • P. malariae infect older RBCs.
    • P. falciparum and P. knowlesi can infect RBCs of all ages.
    • P. vivax requires Duffy antigen on RBC membrane to invade.
    • Genetic traits (sickle cell, thalassemia, G6PD deficiency) confer some resistance to malaria.
  • Microscopy and diagnosis:
    • Thick and thin blood smears; use EDTA venous blood or capillary blood; collect before treatment.
    • Stain with Wright-Giemsa; thin smears regular stain; thick smears water-based Wright-Giemsa for visualization.
    • See Rodak’s chapters for detailed staining guidelines; typically 2–4 technologists review smears.
    • Thick smears for screening; thin smears for speciation and parasitemia percentage.
  • Reporting and tests:
    • A negative smear does not rule out malaria; preliminary report states “No Malarial Parasite Seen” until confirmatory review.
    • Rapid diagnostic tests (BinaxNOW Malaria) detect malaria antigens but do not quantify parasitemia and have limitations at low parasite density.
    • Molecular methods (PCR) detect and speciate malaria; especially helpful for mixed infections and low parasitemia; helpful for P. knowlesi.
  • Specialized notes:
    • Be aware that platelet clumps or platelets on RBCs can be mistaken for malaria on smears.
    • Smear morphology examples: Schuffner stippling in P. vivax/ovale; band form in P. malariae; crescent-shaped gametocytes in P. falciparum; ring forms can be seen in multiple species including Knowlesi.
  • Treatment:
    • Chloroquine or hydroxychloroquine treat all malaria except disease caused by P. falciparum and P. vivax in areas with chloroquine-resistant strains (per sixth edition guidance).

Babesiosis

  • Tick-transmitted protozoan infection; diagnosis by Wright-Giemsa stained peripheral blood smear.
  • Morphology: tiny ring forms that may be round, oval, or tetrad forms; Maltese cross formation (tetrads) is characteristic but not always present.
  • Distinguishing features vs malaria: more pleomorphic rings, absence of hemozoin pigment, no gametocytes, and no extracytoplasmic forms.

Immune Hemolytic Anemia (IHA)

  • Definition: Hemolysis due to antibodies directed against RBC antigens, leading to shortened RBC survival.
  • Antibody types:
    • Autoantibody: against self RBC antigens
    • Alloantibody: against donor RBC antigens (transfusion, pregnancy, organ transplant)
  • Mechanisms of destruction:
    • Some antibodies activate the classic complement pathway (opsonization and removal by spleen).
    • Others cause intravascular complement-mediated hemolysis or primarily extravascular destruction.
    • Hemolysis severity ranges from asymptomatic to life-threatening depending on antibody specificity and activity.
  • Immunoglobulins involved: IgG and IgM are the most common; complement plays a major role in some cases.
  • Diagnostic framework: Direct antiglobulin test (DAT) distinguishes immune from nonimmune hemolysis.
  • Important concept: DAT results may be negative in some immune hemolytic anemias; conversely some disorders yield positive DAT. Context and additional testing (elution, indirect antiglobulin testing) may be required.

DAT Test (Direct Antiglobulin Test)

  • Purpose: Determines if in vivo sensitization of RBC surface is present (IgG, C3b, or C3d).
  • Method: Uses polyspecific anti-human globulin (AHG) that detects Fc portions of IgG and complement components C3b and C3d.
  • Interpretation:
    • Positive polyspecific DAT prompts monospecific testing to identify sensitization type.
    • If IgG detected, an elution procedure is performed to detach antibody for identification (IDAT via indirect antiglobulin test with panel cells).
  • Note: Some immune hemolytic anemias can have a negative DAT; some disorders may yield a positive DAT. Do not rely solely on DAT for diagnosis.

Laboratory Findings in Hemolytic Anemias (General)

  • Common hematologic changes:
    • Decreased hemoglobin (Hb)
    • Increased reticulocytes
    • Increased indirect (unconjugated) bilirubin
    • Increased lactate dehydrogenase (LDH)
    • Decreased haptoglobin
  • If intravascular hemolysis or severe extravascular hemolysis:
    • Plasma hemoglobin (Hb) elevated (hemoglobinemia)
    • Hemoglobinuria or hemosidinuria (chronic hemolysis)
  • MCV may be increased due to reticulocytosis or RBC agglutination if present
  • Peripheral blood smear findings:
    • Polychromasia due to reticulocytosis
    • Spherocytes or schistocytes may be present
    • RBC agglutination depending on condition
    • Erythrophagocytosis
    • NRBCs may be present in severe cases
  • DAT findings:
    • DAT typically positive in immune hemolytic anemias using polyspecific AHG
    • Eluate testing helps identify coating antibodies via IDAT

Autoimmune Hemolytic Anemia (AIHA) Categories

Warm Autoimmune Hemolytic Anemia (WAIHA)

  • Most common AIHA (~70% of cases).
  • Antibody: predominantly IgG; reacts at body temperature (~37°C).
  • Etiology: often idiopathic or secondary to another condition.
  • Hemolysis pattern: predominantly extravascular (spleen removes coated RBCs).
  • Antibody characteristics: warm autoantibodies are usually pan-reactive.
  • DAT: positive in about 95 ext{ extasciitilde{}} ext{%} of cases; some cases yield negative DAT due to various technical reasons (IgA/IgM not detected by polyspecific AHG; low IgG or low avidity; or washing-related dissociation).
  • Management: corticosteroids are initial treatment of choice for non-life-threatening disease; transfusion may be necessary for severe anemia but can be complicated if antibodies react with most donor cells; use limited RBC units and monitor closely.

Cold Agglutinin Disease (CAD)

  • Mostly idiopathic; sometimes associated with malignancies.
  • Antibody: cold agglutinins reacting at ~4°C; primarily IgM.
  • Hemolysis: predominantly extravascular (spleen/phagocytes) with complement involvement; DAT positive for C3 only.
  • Clinical features: winter predominance; acral cyanosis (bluish fingers/toes), numbness; cold-induced agglutination that can activate complement and cause RBC destruction when returning to core body temperature where agglutination resolves but complement remains on RBCs.
  • Lab features: DAT positive for complement only; RBCs show agglutination on smear; MCV may be falsely elevated due to agglutination; RBC agglutination visible on smear.
  • Practical test: warming a sample to 37°C can disperse agglutination to assess underlying state.

Paroxysmal Cold Hemoglobinuria (PCH)

  • Primarily in children; linked to childhood illnesses.
  • Antibody: cold-reacting IgG that binds P antigen on RBCs and fixes complement at low temperature; complement activation at warmer temperatures leads to intravascular hemolysis.

Mixed-type AIHA

  • Features combine warm and cold antibody mechanisms; more complex serologic patterns.

Alloimmune Hemolytic Anemia

  • Occurs when antibodies against foreign RBC antigens are produced via:
    • Transfusion (antibodies against donor antigens)
    • Pregnancy (fetal antigen exposure)
    • Organ transplantation (antibodies against donor organ antigens)

Acute Hemolytic Transfusion Reactions (AHTR)

  • Etiology: predominantly due to acute intravascular hemolysis from ABO incompatibility; typically IgM antibodies.
  • Symptoms: fever, chills, burning at infusion site, nausea, vomiting, chest and back pain.
  • Laboratory findings: hemoglobinemia, hemoglobinuria; elevated unconjugated bilirubin and LDH; decreased haptoglobin; DAT positive.
  • Management: STOP the transfusion immediately.

Delayed Hemolytic Transfusion Reactions (DHTR)

  • Usually due to antibodies against non-ABO RBC antigens (often IgG).
  • Mechanism: secondary (anamnestic) antibody response causing extravascular hemolysis.
  • Typical onset: 2–10 days after transfusion.
  • Lab findings: serological evidence of incompatibility; DAT may be positive.

Hemolytic Disease of the Newborn (HDN)

  • Antibody-mediated destruction of fetal RBCs that cross the placenta; involves maternal alloantibodies against fetal RBC antigens.
  • Pathophysiology and testing similar in concept to other alloimmune hemolytic processes; specific management depends on severity.

Drug-Induced Immune Hemolytic Anemia (DIIHA)

  • Drugs implicated include penicillin, ampicillin, and many cephalosporins.
  • Mechanism:
    • Complement is not usually activated (in typical drug-induced cases).
    • If DIIHA goes unrecognized, drug exposure may continue and risk severe hemolysis.
  • DAT findings: positive for anti-IgG; not typically positive for C3b/C3d in many cases (anti-C3b/C3d may be negative).
  • Mechanism details:
    • Drug binds loosely to the RBC forming a drug-RBC complex that stimulates antibody production (IgG/IgM) which can bind and activate complement.
    • Hemolysis can occur abruptly after exposure or re-exposure.
  • Examples:
    • Drug-dependent antibodies: e.g., penicillin/ampicillin-associated cases.
    • Drug-independent antibodies: e.g., fludarabine-induced warm autoimmune hemolysis (IgG autoantibodies) with extravascular hemolysis.
  • DAT findings: typically IgG positive; complement involvement varies and is usually less prominent than in classic immune complex etiologies.
  • Reference illustration context: Rodak’s Hematology Clinical Principles and Applications; Chapter 23, Fig. 23.6.

Practical and Ethical/Clinical Implications

  • Diagnosis often requires integration of clinical context, DAT results, elution/IDAT studies, and serology, because DAT alone can be misleading (positive or negative in different AIHA contexts).
  • Management must balance rapid control of hemolysis with safety of transfusions (e.g., in WAIHA with broad donor reactivity).
  • In pregnancy-related MAHA (HELLP), multidisciplinary management is vital due to fetal/metal risk and potential need for obstetric intervention.
  • In malaria/babesiosis, accurate species identification and parasitemia quantification are crucial for appropriate therapy and public health reporting; mixed infections may require molecular tests in addition to microscopy.
  • MAHA variants often require urgent treatment due to potential organ injury (brain, kidneys) or loss of renal function (HUS) or neurologic complications (TTP).

References and Acknowledgments

  • Rodak’s Hematology Clinical Principles and Application; Chapter 22 (and 23 for AIHA) – foundational text for these notes.
  • Additional review sources cited in the lecture materials; chapter-and-page references provided in the transcript.