Paroxysmal Nocturnal Hemoglobinuria - PNH

Diagnosis

Indications for Testing

• Patient presenting with anemia and hemolysis

Laboratory Testing

• Initial screen for hemolysis
  • CBC – overt hemolysis on smear (polychromasia); thrombocytopenia and leukopenia may also occur
  • Reticulocyte count – elevated
  • Lactate dehydrogenase (LD) – always elevated
  • Bilirubin – may be elevated
  • Haptoglobin – low
• Ham and sugar tests are obsolete for the diagnosis of PNH due to their nonspecificity and low sensitivity
  • In the rare instance when congenital dyserythropoietic anemia type II is suspected, the Ham test is the preferred initial test
• Flow cytometry of granulocytes and erythrocytes – evaluate for presence of GPI-linked antigens
  • Gold standard for diagnosis of PNH
  • Both WBC and RBC testing are recommended for initial diagnosis
    • WBC testing is best to monitor the PNH clone size
      • Fluorescently labeled inactive toxin aerolysin (FLAER) is included in WBC testing
    • RBC testing is more sensitive for detecting minor PNH clones
    • RBC testing is best for PNH type II and type III quantification
• PIGA gene mutation – confirms flow cytometry results but seldom necessary

Histology

• Bone marrow biopsy – reveals normal to hypercellular marrow with erythroid hyperplasia and normal or nearly normal morphology, or hypocellular or aplastic
  • Indicated when pancytopenia is present to rule out other disorders or when marrow transplantation considered

Differential Diagnosis

• Aplastic anemia
• Other hemolytic diseases or processes
• Myelodysplastic syndromes
• Congenital dyserythropoietic anemia (CDA type II, ie, hereditary erythroblastic multinuclearity with positive acidified serum lysis test [HEMPAS])
• Leukemia (AML, ALL)

Monitoring

Clinical Background

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired clonal disorder caused by the nonmalignant clonal expansion of one or more stem cell lines. PNH results in a deficiency of cell-surface glycophosphatidylinositol (GPI)-anchored proteins, including complement pathway regulatory proteins. PNH is associated with several phenotypes or phenotype combinations, including intravascular hemolysis, thrombotic complication (especially Budd-Chiari syndrome and mesenteric thrombosis), and aplastic anemia.

Epidemiology

• Incidence – 1.3/1,000,000
• Age – median onset is 40 years
• Sex – M:F, equal

Pathophysiology

• Mutation of PIGA gene results in the deficiency or absence of GPI-anchored cell membrane proteins
• Pathophysiology of hemolysis involves abnormal RBC sensitivity to complement lysis
• Pathophysiology of bone marrow failure and thromboses is not known
• Association between acquired aplastic anemia and PNH – majority of patients with PNH will eventually develop some degree of bone marrow failure

Clinical Presentation

• Chronic hemolysis – patient reports episodic occurrence of dark urine (in minority) and hemosiderinuria (in virtually all PNH patients with hemolysis)
• Symptoms of anemia (fatigue, pallor, weakness)
• Thrombophilia (occurs in up to 40% of patients)
  • Thromboses at various sites – abdominal veins most common
    • Thromboses are the leading cause of death in PNH
• Aplastic anemia
  • Overlap syndromes with aplastic anemia
• Other signs and symptoms may include abdominal pain, iron deficiency anemia, jaundice, smooth muscle dysfunction

Treatment

• Based on level of signs and symptoms
  • Minimal – folic acid and thrombosis prophylaxis
  • Intravascular hemolysis of PNH can be controlled with eculizumab, a humanized monoclonal antibody that blocks formation of cytolytic membrane attack complex of complement
    • Eculizumab is palliative and has no effect on the underlying disease process
  • Mutant clone can be eradicated and normal hematopoiesis restored by allogenic hematopoietic stem cell transplant

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory

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Test Name and Number	Comments
Acid Hemolysin (Ham Test) 0049010 Method: Visual Identification	Obsolete for the diagnosis of PNH; preferred initial diagnostic test for PNH is RBC and WBC PNH panel  In the rare instance when congenital dyserythropoietic anemia type II is suspected, this is the preferred initial test

Diagnostic Algorithm

  Hemolytic Anemias Testing Algorithm