Paroxysmal Nocturnal Hemoglobinuria

What is paroxysmal nocturnal hemoglobinuria?

Paroxysmal nocturnal hemoglobinuria (often shortened to PNH) is a rare, acquired blood disorder in which red blood cells are destroyed too early by a part of the immune system called the complement system. The complement system is a group of proteins in the blood that normally helps fight infection. In PNH, some red blood cells are missing the protective surface proteins that would normally tell complement to leave them alone, so these cells break apart inside the blood vessels. This process is called hemolysis, and when it happens inside the vessels it is called intravascular hemolysis.

The name describes what doctors first noticed more than a century ago. "Paroxysmal" means the symptoms come in episodes, "nocturnal" refers to the fact that red cell breakdown was thought to happen mostly at night, and "hemoglobinuria" means hemoglobin (the red, oxygen-carrying protein inside red cells) appears in the urine and turns it dark. In reality, hemolysis in PNH happens around the clock, and many people never notice dark urine at all, so the name can be misleading.

PNH is not inherited and is not contagious. It is an acquired condition, meaning it develops during a person’s lifetime rather than being passed down from parents. It can appear at any age but is most often diagnosed in young and middle-aged adults. Men and women are affected in roughly similar numbers. Because it is rare and its symptoms overlap with many other conditions, the diagnosis is often delayed. PNH is closely linked to other bone marrow disorders, especially aplastic anemia (a condition in which the bone marrow does not make enough blood cells). Care for PNH is usually led by a hematologist, a doctor who specializes in blood disorders; at Acibadem this condition is managed within the Hematology Department.

Paroxysmal nocturnal hemoglobinuria symptoms

Paroxysmal nocturnal hemoglobinuria symptoms vary widely from person to person and depend on how many blood cells are affected, how fast red cells are being destroyed, and whether the bone marrow is also underperforming. Some people have severe, daily symptoms, while others feel relatively well for long periods. Common symptoms include:

• Fatigue that is often out of proportion to the level of anemia (low red blood cell count) and does not improve with rest
• Dark, tea-colored or cola-colored urine, especially the first urine of the morning
• Shortness of breath, particularly with activity
• Abdominal pain, which may come in waves or episodes
• Difficulty or pain when swallowing (dysphagia), caused by spasm of the muscles of the esophagus
• Erectile dysfunction in men
• Yellowing of the skin or eyes (jaundice) from the breakdown products of red cells
• Pale skin, headaches, and a fast heartbeat related to anemia
• Easy bruising, bleeding, or frequent infections when the bone marrow is also failing
• Blood clots, which can cause swelling and pain in a limb, chest pain, sudden breathlessness, severe abdominal pain, or sudden headache

Many of these symptoms are linked to nitric oxide, a natural chemical that helps smooth muscle relax and blood vessels open. Free hemoglobin released from broken red cells binds nitric oxide and removes it from the body. This shortage is thought to explain the muscle spasms that cause abdominal pain and swallowing difficulty, as well as erectile dysfunction, and it may contribute to high blood pressure in the lungs (pulmonary hypertension) and to kidney strain over time.

Blood clots (thrombosis) are the most dangerous complication of PNH. They can form in unusual places, including the veins of the liver, the abdomen, and the brain, as well as in the more familiar locations of the legs and lungs. A clot can be the first sign of PNH in some people who did not know they had the condition.

Doctors often describe three broad patterns of the disease, and symptoms differ between them:

• Classic PNH: a large proportion of blood cells are affected, hemolysis is obvious, and the bone marrow is otherwise producing cells normally. Symptoms of hemolysis and clotting tend to dominate.
• PNH with another bone marrow disorder: PNH occurs together with aplastic anemia or a related condition. Low counts of all blood cell types may cause bleeding and infection in addition to anemia.
• Subclinical PNH: only a very small number of cells are affected and there is no measurable hemolysis. People in this group usually have no PNH-related symptoms, but are monitored because the affected cell population can grow over time.

Causes and risk factors

Paroxysmal nocturnal hemoglobinuria causes lie in a genetic change that happens in a single blood-forming stem cell in the bone marrow. Stem cells are the parent cells that produce all red cells, white cells, and platelets. In PNH, a stem cell develops a mutation (a change in its genetic code) in a gene called PIGA. This mutation is somatic, meaning it occurs in that one cell during life and is not present in the egg or sperm, which is why PNH does not run in families.

The PIGA gene is needed to build a molecular anchor called GPI, which holds a number of protective proteins onto the surface of blood cells. Two of these proteins, known as CD55 and CD59, act as brakes on the complement system. Without the GPI anchor, cells made from the mutated stem cell lack CD55 and CD59, and complement is free to attack them. Red cells are the most obviously affected because they burst, but white cells and platelets made from the same stem cell also lack these proteins, which is thought to contribute to the increased clotting risk.

A PIGA mutation on its own is probably not enough to cause disease; researchers believe that such mutations occur in small numbers in many healthy people without ever causing problems. For PNH to develop, the abnormal stem cell must expand and produce a large share of the blood. Why this happens is not fully understood. A leading theory is that in some people the immune system attacks normal bone marrow stem cells (as happens in aplastic anemia), and the PNH cells, which lack certain surface proteins, escape this attack and gradually take over.

Known associations and risk factors include:

• Aplastic anemia, the strongest known association; a sizeable share of people with aplastic anemia have a detectable PNH cell population
• Other bone marrow failure syndromes, such as certain forms of myelodysplastic syndrome (a group of disorders in which blood cells are poorly formed)
• Previous immune-suppressing treatment for bone marrow failure, after which PNH cells may become more prominent
• Young to middle adult age, when the condition is most often diagnosed

There is no evidence that diet, lifestyle, infections, or environmental exposures cause PNH, and there is nothing a person could have done to prevent it. Certain triggers, such as infections, surgery, or heavy physical stress, can temporarily increase complement activity and set off a hemolytic episode in someone who already has the condition.

Diagnosis

Paroxysmal nocturnal hemoglobinuria diagnosis usually begins when a doctor notices unexplained anemia, signs of red cell breakdown, dark urine, or a blood clot in an unusual place. Because PNH is rare, it is often considered only after more common causes have been ruled out. The following tests are typically used:

• Complete blood count (CBC): measures red cells, white cells, and platelets. In PNH, red cells are usually low; white cells and platelets may also be low if the bone marrow is affected.
• Reticulocyte count: reticulocytes are young red cells. A high count suggests the marrow is working hard to replace destroyed cells; a low count suggests the marrow is failing.
• Lactate dehydrogenase (LDH): an enzyme released when red cells break apart. Very high LDH is a hallmark of intravascular hemolysis and is also used to track disease activity.
• Bilirubin and haptoglobin: bilirubin (a breakdown product of hemoglobin) rises and haptoglobin (a protein that mops up free hemoglobin) falls during hemolysis.
• Direct antiglobulin (Coombs) test: checks for antibodies on red cells. This is negative in PNH, which helps separate it from autoimmune hemolytic anemia.
• Urine tests: may show hemoglobin or hemosiderin (iron deposits from broken cells) even when the urine looks normal.
• Flow cytometry: the definitive test. A blood sample is passed through a laser-based machine that measures proteins on the surface of individual cells. The laboratory looks for cells missing CD55, CD59, and other GPI-anchored proteins, often using a reagent called FLAER that binds directly to the GPI anchor. The result is reported as the percentage of affected cells, sometimes called the "PNH clone size."
• Bone marrow examination: a sample of marrow is taken, usually from the hip bone, to check whether the marrow is producing cells normally or shows signs of aplastic anemia or another disorder.
• Imaging: ultrasound, CT, or MRI scans may be ordered if a blood clot is suspected, particularly in the abdomen or brain, and an echocardiogram may be used to assess pressure in the lungs.

There are no formal scoring criteria for PNH in the way there are for some other diseases. The diagnosis rests on demonstrating a population of GPI-deficient blood cells by flow cytometry, interpreted alongside evidence of hemolysis and the overall clinical picture. Doctors may also screen for PNH in people with aplastic anemia or unexplained clots even when hemolysis is not obvious.

Paroxysmal nocturnal hemoglobinuria treatment options

Paroxysmal nocturnal hemoglobinuria treatment depends on the type of PNH, the severity of symptoms, the degree of hemolysis, and whether the bone marrow is also failing. Treatment aims to control red cell destruction, prevent blood clots, manage anemia, and, where appropriate, address the underlying bone marrow problem. The main approaches are outlined below.

Observation and monitoring

People with subclinical PNH, or with a small clone and no significant hemolysis, may not need disease-specific treatment. Instead, a hematologist typically monitors blood counts, LDH, and clone size at regular intervals, because the affected cell population can grow or shrink over time. Treatment may be started later if hemolysis or symptoms develop.

Complement inhibitor medications

For people with active hemolysis, complement inhibitors are now the standard treatment. These medicines block specific steps in the complement cascade so that it can no longer destroy PNH red cells. The first widely used drugs in this group, eculizumab and ravulizumab, are given by intravenous infusion and block a complement protein called C5. Newer medicines act earlier in the cascade; some, such as pegcetacoplan, are injected under the skin, while others are taken by mouth. Your doctor may recommend one over another based on your response, convenience, and whether some red cells continue to be removed in the liver and spleen despite C5 blockade (sometimes called extravascular hemolysis).

Complement inhibitors often reduce fatigue, lower LDH, decrease the need for transfusions, and lower the risk of clots. They are not a cure: the abnormal stem cells remain, and treatment usually needs to continue long term. Because blocking complement weakens defenses against certain bacteria, especially the type that causes meningococcal meningitis, vaccination is required before starting these drugs, and some people are also given preventive antibiotics. Patients are taught to seek urgent care for fever or other signs of infection.

Supportive treatments

• Blood transfusions to relieve severe anemia when needed
• Folic acid supplements, because rapid red cell production uses up this vitamin
• Iron replacement if iron is lost in the urine, used cautiously since iron can sometimes trigger more hemolysis
• Anticoagulants (blood thinners) to treat a clot that has already formed; in some cases they are also used to prevent clots, though this is less common now that complement inhibitors are available
• Treatment of bone marrow failure, which may include immune-suppressing medicines if aplastic anemia is also present

Bone marrow (stem cell) transplantation

Allogeneic stem cell transplantation, in which a patient’s bone marrow is replaced with healthy stem cells from a donor, is the only treatment that can potentially cure PNH by removing the abnormal stem cells entirely. However, it carries serious risks, including severe infections and graft-versus-host disease (a reaction in which donor cells attack the patient’s body). For this reason it is generally reserved for people with severe bone marrow failure or for those who do not respond to or cannot receive complement inhibitors. The decision is individualized and made with a transplant team.

Surgery and rehabilitation

Surgery is not a treatment for PNH itself. When surgery is needed for another reason, careful planning is important because operations can trigger hemolysis and clotting. Rehabilitation is not routinely required, but people recovering from a clot, especially one affecting the brain or a limb, may benefit from physical therapy. Managing fatigue through paced activity and good sleep habits is often part of ongoing care.

Living with paroxysmal nocturnal hemoglobinuria and outlook

PNH is a chronic condition that in most cases requires lifelong follow-up. In the past, before targeted treatments existed, the outlook was often poor, largely because of blood clots and complications of bone marrow failure. The introduction of complement inhibitors has changed this picture considerably, and many people receiving effective treatment now experience far fewer hemolytic episodes and a much lower clotting risk. Nonetheless, the course of the disease varies, and no treatment can promise a specific outcome.

Several factors influence the outlook, including the size of the PNH clone, the presence and severity of any bone marrow failure, a history of thrombosis, kidney function, and how well the disease responds to therapy. In some people the clone shrinks spontaneously over many years, though this cannot be predicted. Rarely, PNH progresses to another bone marrow disorder, which is one reason regular monitoring matters.

Day-to-day, living with PNH often means keeping up with scheduled infusions or medications, attending regular blood tests, staying current with vaccinations, and being alert to signs of infection or clotting. Many people find it helpful to carry information about their condition and treatment in case of emergencies. Pregnancy is possible for women with PNH but carries increased risks for both mother and baby and requires close, coordinated care from hematology and obstetric teams. Fatigue and the emotional weight of a rare chronic illness are real, and support from family, patient organizations, and mental health professionals can be valuable.

Frequently asked questions

Is paroxysmal nocturnal hemoglobinuria a type of cancer?

No. PNH is a clonal disorder, meaning it arises from a single abnormal stem cell that multiplies, and this feature is shared with some blood cancers. However, PNH cells are not malignant; they do not grow uncontrollably or invade tissues. PNH is classified as a bone marrow failure disorder and an acquired hemolytic anemia. In a small number of people it can evolve over time into a related marrow condition, which is one reason ongoing monitoring is recommended.

What are the first paroxysmal nocturnal hemoglobinuria symptoms people usually notice?

The earliest symptoms are often vague and easily attributed to other things: persistent tiredness, mild breathlessness, or occasional episodes of abdominal discomfort. Dark morning urine is the most recognizable sign but occurs in only a portion of patients. Some people are diagnosed only after a blood clot in an unusual location or after routine blood tests reveal unexplained anemia. If you have several of these features, a doctor can decide whether testing for hemolysis is appropriate.

What causes paroxysmal nocturnal hemoglobinuria, and can it be inherited?

PNH is caused by an acquired mutation in the PIGA gene within a bone marrow stem cell, which leaves the cells it produces without protective surface proteins. Because the mutation happens in body cells during life rather than in egg or sperm cells, it is not passed to children and does not run in families. There is no known way to bring it on or to prevent it, and it is not linked to lifestyle.

How is paroxysmal nocturnal hemoglobinuria diagnosed if the urine looks normal?

Normal-looking urine does not rule out PNH. Doctors rely on blood tests that show red cell breakdown, such as a high LDH, low haptoglobin, and raised bilirubin, together with a negative Coombs test. The diagnosis is confirmed by flow cytometry, a laboratory technique that identifies blood cells lacking the CD55 and CD59 proteins or the GPI anchor. This test is highly sensitive and can detect even small populations of PNH cells.

Can paroxysmal nocturnal hemoglobinuria be cured?

The only treatment with the potential to cure PNH is a stem cell transplant from a donor, which replaces the abnormal bone marrow. Because transplantation carries significant risks, it is usually reserved for people with severe marrow failure or those who cannot be managed with medication. Complement inhibitors control the disease very effectively for many people but do not remove the underlying abnormal cells, so they are typically continued long term.

Does paroxysmal nocturnal hemoglobinuria treatment have side effects?

Complement inhibitors are generally well tolerated, but they increase the risk of serious infection with certain bacteria, particularly those that cause meningococcal disease. Vaccination is required before treatment, and any fever should be treated as urgent. Headache, nausea, and infusion or injection-site reactions can occur. Some people continue to have a milder form of hemolysis despite treatment and may need a change of medicine. Your hematologist will discuss the specific risks of any drug recommended for you.

Can I live a normal life with paroxysmal nocturnal hemoglobinuria?

Many people receiving effective treatment are able to work, study, travel, and have families, although the condition requires ongoing medical care and some planning. Fatigue can be a persistent challenge even when blood tests look good. Staying up to date with treatment schedules, vaccinations, and monitoring, and knowing the warning signs of clots and infection, helps most people manage the condition alongside everyday life. Individual experiences vary, and your care team can give guidance tailored to your situation.

When to see a doctor

You should see a doctor if you have ongoing, unexplained fatigue, shortness of breath, dark urine, or repeated episodes of abdominal pain or difficulty swallowing, especially if blood tests have shown anemia without a clear cause. If you have already been diagnosed with PNH or aplastic anemia, keep your scheduled follow-up appointments even when you feel well, because changes in the disease can occur without obvious symptoms.

Seek emergency medical care immediately if you experience any of the following, as they may signal a blood clot, severe hemolysis, or a serious infection:

• Sudden chest pain or sudden severe shortness of breath
• Sudden, severe headache, confusion, weakness on one side of the body, difficulty speaking, or vision changes
• Severe or rapidly worsening abdominal pain, especially with swelling of the abdomen or vomiting
• Painful swelling, redness, or warmth in an arm or leg
• Fever, chills, stiff neck, or a rash, particularly if you are taking a complement inhibitor
• Very dark urine along with dizziness, fainting, or a racing heartbeat
• Bleeding that will not stop, blood in the stool or vomit, or widespread bruising
• Yellowing of the skin or eyes that appears suddenly or worsens quickly

Blood clots in PNH can develop rapidly and in unexpected locations, and infections in people on complement-blocking treatment can become life-threatening within hours. Early evaluation gives the best chance of effective treatment.