Paroxysmal Nocturnal Hemoglobinuria (PNH)


Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, chronic, acquired, life-threatening hematopoietic stem cell disease that progressively affects multiple body systems. Characteristics of PNH include intravascular hemolytic anemia, thrombosis, smooth-muscle dystonia, serious infections, and bone marrow failure.1,2

In 2010, the International Clinical Cytometry Society (ICCS) published consensus guidelines for the diagnosis, management, and treatment of PNH. In 2017, the ICCS, in collaboration with the European Society for Clinical Cell Analyses (ESCCA), updated its consensus guidelines for PNH.3

In Turkey in 2013, specialists in hematology, immunology, cardiology, neurology, gastroenterology, pulmonology, urology, and general surgery established the PNH Education and Study Group (PESG), with the objective of spreading awareness about PNH. In 2016, the PESG published a summary of the international guidelines related to PNH.4 

In the summer of 2021, the Brazilian Associação Brasileira de Hematologia, Hemoterapia, e Terapia Celular (ABHH) reviewed the literature on the international guidelines for the diagnosis and treatment of PNH and published a consensus statement. They placed a special focus on early recognition of the systemic complications of PNH.1

Diagnosis of PNH

Many current guidelines emphasize the need for laboratory testing, flow cytometry, and bone marrow aspiration and biopsy to diagnose PNH.1,3,4

Laboratory Testing for PNH Diagnosis

In a patient with PNH, blood tests reveal the following1,4:

  • Decreased red blood cell count (anemia)
  • Increased lactate dehydrogenase (LDH) level
  • Increased bilirubin level
  • Increased reticulocyte count
  • Decreased haptoglobin level
  • Decreased hemoglobin

A negative result of a direct antiglobulin (Coombs) test indicates that the anemia is not antibody-mediated (Coombs-negative anemia).1,4

The results of urinalysis are positive for hemoglobinuria. The results of a dipstick test are positive for heme and negative for red blood cell sediment.1

Further screening is warranted if the laboratory findings indicate the presence of intravascular hemolysis in a patient presenting with the most common clinical features of PNH: thrombosis, abdominal or chest pain, dysphagia, dyspnea, and erectile dysfunction.4

Flow Cytometry for PNH Diagnosis

High-precision flow cytometry is the gold standard diagnostic test for PNH. Fluorescently labeled monoclonal antibodies that bind to glycosylphosphatidylinositol (GPI)-anchored proteins are used to detect a deficiency of GPI-anchored proteins, especially CD55 and CD59, in peripheral blood samples,1,4 as well as the levels of other GPI-linked proteins, such as CD14, CD15, CD16, CD24, CD45, and CD64.1 

Fluorescent aerolysin (FLAER) may also be used for assays.1,4 Aerolysin is a toxin derived from bacteria that binds directly to GPI-anchored proteins,1 which are frequently absent in the granulocytes and monocytes of patients with PNH.4 In one pilot study, a FLAER-based assay detected leukocytic PNH clones in a single tube with a high level of diagnostic sensitivity.2

Bone Marrow Aspiration and Biopsy for PNH Diagnosis

Although bone marrow aspiration and biopsy are not specifically required for a diagnosis of PNH, they are highly recommended to assess for bone marrow deficiency caused by comorbidities such as myelodysplastic syndrome (MDS), aplastic anemia (AA), and idiopathic myelofibrosis.4

Read more about PNH diagnosis

PNH Subtypes

The International PNH Interest Group (IPIG) has classified PNH into three subtypes: classic PNH, PNH associated with a specific bone marrow disorder, and subclinical PNH.5

In classic PNH, the clinical and laboratory findings confirm the presence of intravascular hemolysis without evidence of bone marrow deficiency.1

In PNH associated with a specific bone marrow disorder, hemolysis occurs in a bone marrow deficiency disease such as MDS or AA.1

Subclinical PNH occurs without clinical or laboratory confirmation of hemolysis or thrombosis and is often present in patients with other bone marrow conditions.1

Read more about PNH types

Risk Classification of PNH

The level of PNH disease activity can guide treatment decisions and determine the required frequency of monitoring. The following signs are typically observed in patients who have a high level of disease activity and are considered to be at risk4:

  • Anemia (hemoglobin <10 g/dL)
  • Increased hemolysis (LDH >1.5 ULN [upper limit of normal])
  • Hemoglobinuria
  • Weakness
  • Fatigue
  • Dyspnea
  • Major vascular events (including thrombosis, often in atypical locations)
  • Abdominal pain
  • Dysphagia
  • Erectile dysfunction

Read more about PNH prognosis

Treatment Guidelines for PNH

Treatments for PNH include supportive care, allogeneic hematopoietic stem cell transplant (HCT), and complement inhibitors, such as Soliris®.1

Supportive care 

These treatments may include1,4:

  • Oral iron supplementation with additional recommendations for folate and vitamin B12
  • Red blood cell transfusion if a patient’s hemoglobin level drops below recommended levels
  • Immediate treatment of bacterial infections with antibiotics to prevent hemolytic crises
  • Short-term glucocorticoids to decrease the duration and severity of hemolytic crises
  • Immunosuppression in patients who have PNH with comorbid AA or bone marrow deficiency
  • Primary anticoagulation prophylaxis to prevent thrombotic events in patients with PNH who are pregnant, are not taking complement inhibitors, are perioperative, have high D-dimer levels, or have a high PNH clone size with other risk factors for thrombosis

Read more about PNH treatment

Allogeneic HCT

Allogeneic hematopoietic stem cell transplant is a potentially curative treatment reserved for those patients most severely affected by PNH. This may include patients with significant comorbidities, those at risk for mortality, and patients unresponsive to other treatments. There is high risk for post-transplant infection and mortality, so this must be factored into the decision for treatment.1

Read more about PNH experimental therapies

Complement Inhibitors

Three complement inhibitors have been approved by the US Food and Drug Administration (FDA) for the treatment of PNH: Soliris® (eculizumab) in 2007, Ultomiris® (ravulizumab) in 2018, and Empaveli™ (pegcetacoplan) in 2021. Soliris and Ultomiris block activation of the complement system by binding to C5 and preventing it from splitting into C5a and C5b, while Empaveli inhibits the C3 complement protein from fragmenting into a C3b activation.6 All three drugs decrease PNH-induced organ damage due to hemolysis, renal failure, thrombosis, and pulmonary hypertension and reduces the need for transfusions.4 

Patients taking complement inhibitors should be routinely monitored with the following tests1:

  • Complete blood cell (CBC) count with differential, reticulocyte count, LDH measurement, and biochemical analysis every month for the first 3 months and then every 3 months
  • Renal function tests, including measurement of electrolytes, the estimated glomerular filtration rate, and urea every 3 months
  • Iron studies, including ferritin and transferrin saturation, every 3 months
  • Tests to detect folic acid and vitamin B12 deficiency yearly
  • Updates on transfusion history every 6 months
  • PNH clone analysis every 6 months for the first 2 years, then every year in patients with stable PNH

Discontinuation of complement inhibitors should be considered in the following cases1:

  • Spontaneous disease remission
  • Reduction of the red blood cell transfusion requirement of less than 30% during the 6 months after the initial dose
  • Continued significant hemolysis following the initial dose
  • Onset of significant bone marrow failure
  • Patient’s desire to stop treatment or lack of patient adherence to monitoring and treatment protocols

Read more about PNH therapies

References

  1. Cançado RD, Araújo A da S, Sandes AF, et al. Consensus statement for diagnosis and treatment of paroxysmal nocturnal haemoglobinuria. Hematol Transfus Cell Ther. 2021;43(3):341-348. doi:10.1016/j.htct.2020.06.006
  2. Manivannan P, Tyagi S, Pati HP, Saxena R. FLAER based assay according to newer guidelines increases sensitivity of PNH clone detection. Indian J Hematol Blood Transfus. 2020;36(3):526-534. doi:10.1007/s12288-019-01220-8
  3. Sutherland DR, Illingworth A, Marinov I, et al. ICCS/ESCCA consensus guidelines to detect GPI-deficient cells in paroxysmal nocturnal hemoglobinuria (PNH) and related disorders part 2 – reagent selection and assay optimization for high-sensitivity testing.  Cytometry B Clin Cytom. 2018;94(1):23-48. doi:10.1002/cyto.b.21610
  4. Sahin F, Akay OM, Ayer M, et al. PESG PNH diagnosis, follow-up and treatment guidelines. Am J Blood Res. 2016;6(2):19-27.
  5. Dezern, AE and Borowitz, MJ. ICCS/ESCCA consensus guidelines to detect GPI-deficient cells in paroxysmal nocturnal hemoglobinuria (PNH) and related disorders part 1 – clinical utility. Cytometry B Clin Cytom. 2018;94(1):16-22. doi:10.1002/cyto.b.21608
  6. Besa EC. Paroxysmal nocturnal hemoglobinuria treatment & management: approach considerations. Medscape. Updated May 20, 2021. Accessed December 5, 2022.

Reviewed by Kyle Habet, MD, on 11/29/2022.