Why Do PNH Patients Still Need Blood Transfusions on C5?

If you have Paroxysmal Nocturnal Hemoglobinuria (PNH) and take a complement inhibitor like eculizumab or ravulizumab, it can be incredibly frustrating to still feel fatigued and require regular blood transfusions. Continued anemia does not necessarily mean the C5 inhibitor is doing nothing—it is likely still protecting you from severe intravascular hemolysis and significantly lowering your risk of blood clots. However, persistent transfusions deserve a structured evaluation to find the cause.

One common explanation is a process called extravascular hemolysis (EVH). While C5 inhibitors are excellent at stopping red blood cells from being destroyed inside your blood vessels, they do not stop them from being tagged for destruction outside your blood vessels in organs like the spleen and liver ^[1][2].

The Two Types of Hemolysis

To understand why transfusions might still be needed, it helps to look at how the complement system—a part of your immune system—attacks PNH red blood cells.

• Intravascular Hemolysis (Inside the blood vessels): This occurs when the complement system punches holes in red blood cells while they are circulating in the bloodstream. C5 inhibitors (eculizumab and ravulizumab) block the very end of this attack process. They are highly effective at preventing intravascular hemolysis and substantially reducing the life-threatening risks associated with it, such as blood clots ^[1].
• Extravascular Hemolysis (Outside the blood vessels): Even though C5 inhibitors stop the final attack, the early parts of the complement cascade are still active. A complement protein called C3 can attach itself to (or “tag”) the surface of your surviving PNH red blood cells ^[1][3]. When these tagged cells travel through the spleen or liver, immune cells recognize the C3 tags and remove the red blood cells.

Because EVH continues despite C5 inhibitor treatment, your hemoglobin level and red blood cell count can remain low, leading to persistent fatigue and a continued need for transfusions ^[4][5]. Clinical trials have found that about 20% to 25% of PNH patients on a C5 inhibitor experience clinically significant EVH (defined in those studies as symptomatic anemia with high reticulocytes) ^[4][6].

Are There Other Reasons for Low Hemoglobin?

While EVH is a common culprit, it is not the only reason a patient on a C5 inhibitor might remain anemic. Before changing your treatment, your doctor should evaluate you for other factors ^[7][8]:

• Bone Marrow Failure: PNH is closely related to conditions like aplastic anemia. If your bone marrow is not producing enough red blood cells to begin with, stopping hemolysis will not fully resolve your anemia.
• Breakthrough Hemolysis: Sometimes intravascular hemolysis temporarily returns. This can happen if the drug concentration drops near the end of a dosing cycle, or if an infection, surgery, or pregnancy triggers a massive complement response that overwhelms the medication ^[5][9].
• Nutritional Deficiencies and Iron Overload: Lack of iron, vitamin B12, or folate can prevent your body from making enough red blood cells. Do not start iron supplements on your own, however, because receiving regular blood transfusions can actually cause dangerous iron buildup (iron overload) that requires separate management ^[7][8].
• Other Factors: Bleeding, kidney disease, or other inflammatory conditions can also contribute to anemia.

Understanding Your Lab Tests

Your doctor will look at several tests to determine the cause of your anemia ^[10][11][12]:

• LDH (Lactate Dehydrogenase): An enzyme released when red blood cells break open. It is a key marker of intravascular hemolysis.
• Reticulocyte Count: A measure of newly produced red blood cells, showing how hard your bone marrow is working.
• Direct Antiglobulin Test (DAT or Coombs Test): Looks for antibodies or complement (like C3) coating your red blood cells. A positive C3 test is common on C5 inhibitors, but it is not a standalone measure of treatment effectiveness; it must be interpreted alongside your other labs and symptoms.

New Treatment Options: Proximal Inhibitors

If your care team confirms that EVH is the main reason for your persistent anemia, there are medications designed to block the complement system earlier (proximally), preventing C3 tags from building up in the first place ^[13].

• Pegcetacoplan (C3 Inhibitor): Given as a twice-weekly subcutaneous infusion (under the skin, sometimes requiring a pump device). In the phase 3 PEGASUS trial of adults who remained anemic on eculizumab, it was superior for improving hemoglobin, and 85% of patients taking pegcetacoplan avoided transfusions over 16 weeks (compared to 15% on eculizumab) ^[14][15].
• Iptacopan (Factor B Inhibitor): An oral pill taken twice daily. In the phase 3 APPLY-PNH trial of patients with persistent anemia on anti-C5 therapy, 51 of 60 patients taking iptacopan achieved a hemoglobin increase of at least 2 g/dL without transfusions over 24 weeks ^[10].
• Danicopan (Factor D Inhibitor): An oral pill taken three times a day as an add-on therapy. You take it alongside your current C5 inhibitor. In the phase 3 ALPHA trial, adding danicopan significantly improved hemoglobin and reduced transfusions while maintaining intravascular hemolysis control ^[3][16].

Note: Medication availability, age requirements, and approval status vary by country. Do not stop or switch complement inhibitors without a specialist-directed transition plan, as missed doses can trigger severe, life-threatening hemolysis.

⚠️ IMPORTANT SAFETY WARNINGS FOR ALL COMPLEMENT INHIBITORS

• Serious Infection Risk: Both C5 and proximal inhibitors increase the risk of life-threatening infections from encapsulated bacteria, including meningococcal, pneumococcal, and Haemophilus influenzae. You must receive specific vaccines at least 2 weeks before starting treatment ^[17]. If treatment must start sooner, preventive antibiotics may be used.
• Vaccines do not eliminate the risk. Seek immediate emergency medical care if you develop a fever, severe headache, neck stiffness, rash, or confusion ^[17].
• Blood Clot Risk: While treatment lowers the risk of thrombosis, it does not eliminate it ^[8][18]. Seek urgent care for new limb swelling, chest pain, shortness of breath, severe abdominal pain, or neurologic symptoms.
• Breakthrough Hemolysis: Do not wait for your next dose if you experience sudden dark urine, jaundice, abrupt worsening fatigue, or abdominal/back pain. Contact your hematology team promptly.