PNH diagnosis and testing
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The gold standard method for diagnosing paroxysmal nocturnal hemoglobinuria (PNH), a rare acquired disease characterized by the lack of certain proteins on the surface of blood cells, particularly red blood cells, is a molecular examination of those cells to look for these surface proteins. Other tests can be done to assess disease severity and identify a patient’s risk of related disorders.
How is PNH diagnosed?
PNH is caused by mutations in hematopoietic stem cells (HSCs), which reside in the bone marrow and are responsible for giving rise to new blood cells. A mutation in the PIGA gene impairs the production of a molecule called glycosylphosphatidylinositol (GPI), which acts as an anchor to attach other proteins to the cell’s surface. These include a protein called CD59, also known as membrane inhibitor of reactive lysis (MIRL), and another called CD55, which also is known as decay accelerating factor (DAF).
A technique called flow cytometry is considered the gold standard method of diagnosing PNH. It does so by measuring the levels of CD59, CD55, and GPI on blood cells, which are either low or undetectable in people with PNH.
Other tests are often performed to exclude other potential causes, such as autoimmune diseases and bone marrow disorders. Clinicians also will typically ask about a person’s history of aplastic anemia, a bone marrow disorder that increases the risk of PNH.
Flow cytometry
When testing for PNH with flow cytometry, cells are first stained with fluorescent antibodies against CD59 and CD55, as well as a substance that binds to GPI, called fluorescent aerolysin reagent (FLAER). After this, cells pass through a specialized machine called a flow cytometer that analyzes them one by one to measure the fluorescent staining — and, by extension, the amount of CD59, CD55, and GPI on each of them.
Low or absent levels of CD59, CD55, and GPI on blood cells indicates that a person meets the diagnostic criteria for PNH. Disease severity can be assessed based on the proportion of affected cells.
It is necessary to test for both CD59 and CD55 because some people are born without the ability to produce one of these two proteins. If only one of the proteins is analyzed, that can lead to false positives during testing. Additionally, flow cytometry testing must be performed on at least two different blood cell types to minimize the risk of false-positive test results.
Lactate dehydrogenase (LDH) test
Lactate dehydrogenase, also called lactic acid dehydrogenase or LDH, is a protein found in most body cells that is important for regulating energy metabolism. LDH is released into the bloodstream when blood cells are destroyed, which is what happens in PNH. Measuring LDH levels in the blood can therefore be used to assess the severity of PNH.
Bone marrow tests
PNH is caused by a genetic mutation that arises in HSCs, which reside in the bone marrow. Thus, bone marrow tests such as biopsy or aspiration, which involve collecting a sample of bone marrow cells for analysis, may be included in the diagnostic workup of PNH.
Bone marrow tests are usually not needed to diagnose PNH itself, but they can be useful for identifying other bone marrow disorders, such as myelodysplastic syndromes (MDS) and aplastic anemia. People with PNH are at an increased risk of developing some of these bone marrow disorders.
Who diagnoses PNH?
Given that PNH is a rare disease, visiting a specialist in blood disorders — known as a hematologist — may help confirm the diagnosis and rule out other possible conditions causing similar symptoms. Once PNH is suspected, diagnosing the disease with flow cytometry is usually fairly straightforward.
What happens if PNH goes undiagnosed?
Because PNH is a rare condition, it’s common for clinicians not to consider it as a possibility, which can lead to incorrect diagnoses and diagnostic delays. Also, a correct diagnosis is required before proper treatment can be started, so a missed or delayed diagnosis can lead to a longer time to therapy initiation.
Modern care for PNH involves medications that block the activity of the complement cascade, a part of the immune system that plays a central role in this disorder.
Without complement-blocking medications, people with PNH typically live for 10 to 22 years. But for patients on these modern therapies, life expectancy is comparable to that of the general population.
Next steps after PNH diagnosis
After a diagnosis of PNH is confirmed, patients and clinicians will collaborate to develop a care strategy. This usually involves medications that block the activity of the complement system, such as Soliris (eculizumab) and Ultomiris (ravulizumab). These therapies can help reduce the destruction of blood cells that characterizes PNH and drives its symptoms.
In some cases, an allogeneic hematopoietic stem cell transplant — also known as bone marrow transplant — may be performed. The aim of this procedure is to replenish the bone marrow with healthy cells obtained from a donor without the disorder. A stem cell transplant is considered the only truly curative treatment for PNH. However, because it is an invasive procedure that carries not-insubstantial risk, it is not recommended in all cases.
Other care and management strategies for PNH will be tailored to address specific disease symptoms and manifestations. For example, patients with PNH may require oral iron and folic acid supplements, and sometimes blood transfusions.
Across the PNH News website, information and resources can be found to help people become more familiar with the disease.
PNH News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
FAQs about PNH diagnosis
Paroxysmal nocturnal hemoglobinuria (PNH) can develop any age, but the disease, characterized by the lack of certain proteins on the surface of blood cells, most commonly starts and is diagnosed between the ages of 30 and 40.
Flow cytometry is considered the gold standard method for diagnosing paroxysmal nocturnal hemoglobinuria (PNH). This type of test looks for certain proteins on the surface of blood cells, which are typically missing in people with the disorder. False-positive and false-negative test results were common a few years ago, but since then, efforts have been made to standardize the procedure and improve its sensitivity. Now, flow cytometry is considered a highly sensitive and specific test for PNH.
Paroxysmal nocturnal hemoglobinuria (PNH) has been reported in children as young as 3. However, it is more common for the disease to develop during adulthood, usually when patients are in their 30s.
Without a correct diagnosis, a person with paroxysmal nocturnal hemoglobinuria (PNH) cannot start proper treatment. As a result, the disease will continue unchecked, which can lead to severe and life-threatening complications. Without modern therapy, people with PNH typically have lived for a decade or two after disease onset. However, with modern treatments, life expectancy for someone with PNH is comparable to that of the general population.
Paroxysmal nocturnal hemoglobinuria (PNH) is usually diagnosed via flow cytometry, a test that looks for certain proteins on the surface of blood cells that are either missing or present in low levels in people with the disorder. Diagnosing aplastic anemia requires a bone marrow biopsy to assess the number of different blood cell types in the bone marrow. Flow cytometry alone cannot diagnose aplastic anemia, and a bone marrow biopsy is usually not sufficient to diagnose PNH. Given that these two conditions commonly co-occur, it’s typical for both diagnostic tests to be performed if even one of these diseases is suspected.
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