Why does a flow cytometry report show a 68% PNH clone in granulocytes but only an 18% clone in red blood cells? Why do 25% to 35% of patients receiving intravenous C5 inhibitors (ravulizumab or eculizumab) normalize their lactate dehydrogenase (LDH) yet remain fatigued with a hemoglobin of 9.2 g/dL?
For 18 years (2003 to 2021), PNHdisease.org served as the primary online support and clinical education hub for families navigating Paroxysmal Nocturnal Hemoglobinuria. Rebuilt in 2026 as an independent, advertising-free hematology reference desk, this atlas translates high-sensitivity flow cytometry, intravascular vs. extravascular hemolysis markers, and the new generation of oral and subcutaneous proximal complement inhibitors into decision-ready clinical tables.
Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired somatic PIGA stem cell disorder in which blood cells lack glycosylphosphatidylinositol (GPI) anchor proteins CD55 and CD59. Unchecked complement activation lyses red blood cells and triggers venous thrombosis. Modern terminal C5 and proximal C3, Factor B, and Factor D inhibitors restore near-normal life expectancy.
Go to an Emergency Department immediately if you have PNH and develop unexplained severe abdominal pain (possible hepatic or mesenteric vein thrombosis), sudden severe headache, chest pain, dark cola-colored urine after an infection, or any fever of 38.0°C (100.4°F) or higher while taking a C5, C3, Factor B, or Factor D complement inhibitor. See the printable ER Physician Triage Card.
High-sensitivity flow cytometry (sensitivity down to 0.01%) frequently detects minute GPI-deficient clones in patients with acquired aplastic anemia (AA) or hypoplastic myelodysplastic syndrome (MDS). At <1% clone size, serum LDH is normal (<1.5x ULN) and clinical intravascular hemolysis is absent. The presence of a minor PNH clone is actually a favorable biomarker predicting higher response rates to immunosuppressive therapy (ATG + cyclosporine).
Clinical Action: Repeat high-sensitivity flow cytometry every 6 to 12 months; complement inhibitor therapy is not indicated. Read AA & MDS Overlap Dossier.
Patients with a 1% to 10% granulocyte clone typically fall into the IPIG category of PNH in the setting of another specified bone marrow disorder. Cytopenias (thrombocytopenia, neutropenia, hypoproliferative anemia) are driven primarily by marrow hypoplasia rather than complement-mediated red cell lysis. However, clones can expand rapidly during recovery from immunosuppressive therapy.
Clinical Action: Track LDH, reticulocyte count, and haptoglobin every 3 to 6 months. Treat underlying marrow failure first unless LDH rises above 1.5x ULN with hemolytic symptoms. See Flow Cytometry Decoder.
In the 10% to 49% clone range, clinical expression depends heavily on the proportion of Type II (partially CD59-deficient) vs. Type III (completely CD59-deficient) erythrocytes and whether the patient has active intravascular hemolysis (LDH >= 1.5x upper limit of normal). Patients with Type III dominance, LDH >= 1.5x ULN, symptomatic anemia, smooth muscle dystonia, or any prior thromboembolism qualify for complement inhibition.
Clinical Action: Compare Terminal C5 vs. Proximal Complement Inhibitors and screen for abdominal/cerebral thrombosis risks.
| Diagnostic Parameter | Typical Untreated Finding | Pathophysiological Mechanism | Target on Complement Therapy |
|---|---|---|---|
| Granulocyte & Monocyte FLAER | 50% to 99% GPI-deficient | True measure of PIGA mutant stem cell dominance in bone marrow (unaffected by red cell lysis). | Clone % remains high (or rises slightly as RBCs survive); therapy blocks lysis, not the clone itself. |
| RBC CD59 (Type III) Clone | Often 15% to 45% (falsely low) | Type III RBCs lack CD59 entirely and are destroyed by membrane attack complex (C5b-9) or diluted by transfusions. | Type III RBC % rises toward granulocyte % once complement blockade prevents premature lysis. |
| Serum LDH (Lactate Dehydrogenase) | 3.0x to 10.0x ULN (>750 to 2,500+ U/L) | Direct biomarker of intravascular hemolysis (IVH) and cell-free hemoglobin release into plasma. | <1.5x ULN (normal or near-normal), cutting thromboembolic risk by >85%. |
| Reticulocytes & Direct Coombs (C3d) | Reticulocytes >120 x 10^9/L; Coombs negative pre-treatment | Marrow compensation for hemolysis. On C5 inhibitors, surviving RBCs accumulate surface C3d fragments. | If Hb stays <10.5 g/dL with high reticulocytes & C3d+ on C5 therapy, switch to proximal C3/Factor B/D blockade. |
Normal red blood cells carry two critical GPI-anchored shields: CD55 (Decay-Accelerating Factor), which dismantles upstream C3 convertases, and CD59 (MIRL), which blocks downstream C5b-9 Membrane Attack Complex (MAC) pores. When a terminal C5 inhibitor blocks C5 cleavage alone, CD59 absence is compensated, but CD55 absence remains unaddressed.
Enter your most recent laboratory values below to see how hematologists classify intravascular hemolysis activity and whether persistent anemia on a C5 inhibitor points toward C3d-mediated extravascular clearance.
Every dossier is written in plain language, anchored to peer-reviewed trials and guidelines, and mirrored across English, Spanish, and Simplified Chinese.
Why granulocyte FLAER clone size differs from RBC clone size, Type I/II/III red cell populations, and why chronic hemolysis causes the renal cortical hemosiderosis rim sign on CT and MRI.
Head-to-head comparison of Ravulizumab (Ultomiris), Eculizumab (Soliris & biosimilars), Pegcetacoplan (Empaveli), Iptacopan (Fabhalta), Danicopan (Voydeya), and Crovalimab (Piasky).
Managing nitric-oxide-depletion fatigue, why unmonitored iron supplementation triggers hemolytic crises when starting therapy, travel checklists, and MenACWY + MenB schedules.
Budd-Chiari hepatic vein thrombosis, portal/mesenteric clots, cerebral venous sinus thrombosis, and how to manage infection-triggered breakthrough hemolysis (BTH).
Why 40% to 50% of acquired aplastic anemia patients harbor a PNH clone, the auto-immune T-cell escape hypothesis, and sequencing ATG + cyclosporine + eltrombopag with complement blockade.
Why estrogen contraception is contraindicated, NEJM evidence for eculizumab safety in pregnancy, LMWH anticoagulation through 6 weeks postpartum, and pre-surgical dosing.
Comparing $450,000-$550,000/yr US list prices, FDA/EMA eculizumab biosimilars (Bkemv, Epysqli), UK NHS national commissioning, Latin America, and China NRDL reimbursement + HSCT centers.
Concordance of historical PNH Support Group resources, verified international patient advocacy organizations (AAMDSIF, PNH Support UK, HPN Espana, AAMAC), and editorial methodology.
Direct, link-free clinical answers grounded in ASH, IPIG, and Phase 3 complement inhibitor trial evidence.
No. PNH is not leukemia or a malignant cancer, and it never metastasizes to solid organs. It is a benign acquired clonal disorder of hematopoietic stem cells caused by a somatic mutation in the PIGA gene. However, because PNH shares deep bone marrow biology with aplastic anemia and myelodysplastic syndrome (MDS), a small minority of patients (roughly 2% to 5% over 10 years) can evolve into MDS or acute myeloid leukemia, requiring regular complete blood count monitoring.
Clinical source: Parker et al., Blood 2005 (IPIG Consensus) · See AA & MDS Overlap.
Laboratories diagnose PNH using high-sensitivity multiparameter flow cytometry on peripheral blood. In red blood cells, testing measures the GPI-anchored complement regulators CD55 and CD59 to classify cells into Type I (normal), Type II (partial deficiency), and Type III (complete deficiency). In white blood cells (granulocytes and monocytes), laboratories combine FLAER (fluorescently labeled inactive aerolysin, which binds directly to the GPI anchor) with lineage markers such as CD15, CD24, CD14, and CD64.
Clinical source: Borowitz et al., Cytometry Part B 2010 · See Flow Cytometry Decoder.
Before the approval of eculizumab in 2007, median survival after a PNH diagnosis was 10 to 15 years, with venous thrombosis accounting for up to two-thirds of deaths. Today, long-term registry studies from the UK, US, and Europe demonstrate that PNH patients treated with terminal C5 inhibitors (eculizumab or ravulizumab) or proximal complement inhibitors who do not have severe underlying bone marrow failure achieve a life expectancy matching age-matched healthy controls.
Clinical source: Kelly et al., Blood 2011; Kulasekararaj et al., Ann Hematol 2025.
Although the disease was named in the 19th century for dark morning urine (caused by mild respiratory acidosis during sleepenhancing complement activation and concentrated overnight urine), chronic low-grade intravascular hemolysis occurs 24 hours a day. Roughly 70% to 75% of newly diagnosed patients present with crushing fatigue, anemia, smooth muscle spasms, or unexplained thrombosis rather than visible macroscopic hemoglobinuria.
Clinical source: Brodsky, NEJM 2014 / Blood 2021 Review · See Living With PNH.