What is the diagnosis of Paroxysmal Nocturnal Hemoglobinuria (PNH)?

From the Guidelines

Paroxysmal nocturnal hemoglobinuria (PNH) should be diagnosed through a combination of clinical evaluation, complete blood count, and specialized laboratory testing, including flow cytometry of peripheral blood to detect the absence or reduced expression of GPI-anchored proteins, as recommended in the diagnostic work-up for autoimmune hemolytic anemia 1. The diagnostic work-up for PNH, as outlined in the management of immune-related adverse events in patients treated with immune checkpoint inhibitor therapy, should include a history and physical examination, blood chemistry, CBC with evidence of anemia, macrocytosis, evidence of hemolysis on peripheral smear, LDH, haptoglobin, bilirubin, reticulocyte count, free hemoglobin, and PNH screening 1. Some key points to consider in the diagnosis of PNH include:

• History and physical examination to identify potential causes of hemolysis
• Complete blood count to evaluate for anemia, macrocytosis, and evidence of hemolysis
• Specialized laboratory tests, such as flow cytometry, to detect the absence or reduced expression of GPI-anchored proteins
• Evaluation for other potential causes of hemolysis, including autoimmune serology, disseminated intravascular coagulation panel, and infectious causes 1. It is essential to note that early diagnosis of PNH is crucial to prevent serious complications, such as thrombosis, chronic kidney disease, and pulmonary hypertension, and to initiate effective treatments like eculizumab or ravulizumab, which can significantly improve outcomes and quality of life.

From the Research

Diagnosis of Paroxysmal Nocturnal Hemoglobinuria

• The diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) involves detecting the absence of glycosylphosphatidylinositol (GPI)-anchored proteins, such as CD55 and CD59, on the surface of blood cells 2, 3, 4.
• Flow cytometry has become the gold standard for PNH testing, and it is essential to test at least two GPI-linked markers on at least two different lineages, particularly on red cells and granulocytes/monocytes 3, 4.
• The fluorescent aerolysin combined with other monoclonal antibodies in multicolor flow cytometry offers an improved assay for diagnosis and monitoring of PNH clones 3, 4.
• Other laboratory tests, such as the sucrose hemolysis test and Ham's acid hemolysis test, can also be used for screening and confirmation of PNH, but they have been largely replaced by flow cytometric procedures 4.
• A clinically relevant, consensus-driven screening and diagnostic algorithm has been developed to assist non-specialist clinicians in identifying signs and symptoms of PNH and conducting appropriate differential diagnosis 5.

Diagnostic Approaches

• The diagnosis of PNH can be straightforward when flow cytometric analysis of the peripheral blood reveals a population of GPI anchor protein-deficient cells 6.
• However, PNH is clinically heterogeneous, and the disease process can be characterized by florid intravascular, complement-mediated hemolysis, or bone marrow failure can dominate the clinical picture 6.
• An understanding of the unique pathobiology of PNH, including its relationship to complement physiology and immune-mediated bone marrow failure, provides the basis for a systematic approach to management 6.

Laboratory Abnormalities

• Diverse laboratory abnormalities can be observed in PNH, including bone marrow hyper- and hypoplasia, hematologic cytopenias, micro- and macrocytosis, decreased leukocyte alkaline phosphatase (LAP), hemoglobin- and hemosiderinuria, and associated iron deficiency 4.
• These abnormalities can be used to support the diagnosis of PNH, but they are not specific to the disease and can be seen in other conditions as well 4.