How many PNH patients actually reach treatment?

In the UK, 38% of patients known to the national PNH service are on NHS-funded complement inhibition. The National PNH Service at Leeds and King’s College Hospital followed 1,146 patients in 2024–25. Of those, 439 (38%) were on NHS-funded complement inhibition, and 39 started treatment during the year. For anyone forecasting a PNH drug, the gap between “has PNH” and “is treated” is the model.

Updated November 2026 · Every figure checked against the original paper or the service’s own report

What is PNH, and why is it a useful test case?

PNH (paroxysmal nocturnal haemoglobinuria) is a rare acquired blood disorder. Blood cells lose proteins that protect them from the complement system, so red cells break down inside the blood vessels. The results are anaemia, fatigue, dark urine and a high risk of blood clots.

PNH is a good test case for patient flow because each step is unusually well measured. The UK runs a single national service, a population study has counted cases, and an international registry has followed thousands of patients. This post walks the six steps from our pillar post on patient flow models, using PNH numbers at each one.

Step 1: who has PNH?

It depends on what counts as PNH. A Yorkshire study covering 3.8 million people found 197 patients with detectable PNH cells between 2004 and 2018. Only 8% had classical PNH. 88% had aplastic anaemia with a PNH clone, and 3% had myelodysplastic syndrome.

Scaled to the UK, that is about 220 new cases a year and about 2,400 people living with detectable PNH cells. The authors stress that classical haemolytic PNH is a small part of that total. A model that starts from 2,400 and applies a treatment rate overstates the pool for a drug aimed at haemolysis.

Step 2: how long does diagnosis take?

Often years. In a Japanese claims database, 160 patients were diagnosed with PNH between 2010 and 2022. The median time from first PNH-related symptom to diagnosis was 26.5 months. Only 99 of the 160 had the flow cytometry test that is the diagnostic standard. Complication rates, including kidney failure and thrombosis, rose with the length of the delay.

A review funded by a PNH drug maker puts it more broadly. Fewer than 40% of patients are diagnosed within 12 months of symptoms, and 24% take 5 years or longer. For the model, the diagnosed share is an input with its own evidence and its own trend. A new test pathway or an awareness programme can move it.

Step 3: who reaches specialist care?

In the UK, all patients are under review at one of two reference centres. NHS England commissions PNH care from Leeds and King’s College Hospital. In 2024–25 they followed 1,146 patients: 722 at Leeds, covering England, Scotland, Wales and Northern Ireland, and 424 at King’s.

That gives a UK model something rare: a counted specialist-care step. Where no national service exists, that step has to be built from haematology centre counts, registry enrolment or claims data.

The 1,146 cannot simply be divided by the 2,400. The two counts come from different years and different definitions, and the service sees all four UK nations. What they do show is that the specialist-care pool and the population estimate are the same order of size.

Step 4: who is eligible for treatment?

Fewer than the diagnosed count suggests, because clone size and disease activity decide eligibility. The International PNH Registry reported on 4,439 untreated patients, of whom 2,701 had clone size data. The median clone was 31.8%. 1,002 patients had clones under 10%, and 1,173 had clones of 50% or more.

Clone size tracks disease activity. Among untreated Registry patients, high disease activity at last follow-up affected 14% of those with clones of 5% or less. It affected 77% of those with clones above 30%. Small clones still carry risk, though: 10.2% of patients with clones under 10% had a history of major vascular events.

Eligibility is set by the label, then narrowed or widened by the payer and the treating centre. In the UK service, the reasons for starting treatment in 2024–25 are published. Of 39 new starts, 28 were for haemolysis with anaemia, 4 for thrombosis, 5 by exceptional multidisciplinary decision and 2 before a bone marrow transplant.

Step 5: who is treated?

In the UK service, 439 of 1,146 patients (38%) were on NHS-funded complement inhibition. Another 24 were on a trial or non-NHS-funded inhibitor, and 683 (60%) were not on complement inhibition. The report does not say why. The Yorkshire split suggests many have small clones and marrow failure, and are monitored rather than treated.

The share has held steady. In 2020, the Leeds service had 618 patients, 237 of them (38%) on anti-complement therapy.

The treated share has also been measured internationally. In the first 1,610 International PNH Registry patients, 25% were on eculizumab. That figure predates most of today’s medicines.

The choice of medicine has widened fast. The FDA approved eculizumab for PNH in 2007 and ravulizumab in 2018. Pegcetacoplan followed in 2021, iptacopan in 2023, and danicopan and crovalimab in 2024. Two eculizumab biosimilars were also approved in 2024. The UK service lists iptacopan, danicopan and crovalimab as approved since 2024. A forecast now has to split the treated pool by medicine, not just count it.

In PNH, clone size and active haemolysis set the treated pool more than the number of people with the disease.

Step 6: who stays on treatment, and how well does it work?

Complement inhibition changed survival. At Leeds, 79 patients treated with eculizumab between 2002 and 2010 had survival no different from age- and sex-matched controls. 40 of 61 patients (66%) on eculizumab for more than 12 months became transfusion independent.

The full UK record is more mixed. All 509 UK patients treated with eculizumab or ravulizumab up to 2022 had lower survival than matched controls. Among the 389 who did not need treatment for marrow failure, survival matched the controls. Even so, 26.7% needed transfusions in their most recent 12 months on therapy.

Response is often incomplete, and that is where switching comes from. In a German centre, 76 patients on eculizumab were followed for a mean of 5.59 years. 63% were transfusion dependent at some point, and 43% had haemolysis return while on treatment. Between 79% and 89% did not reach a normal haemoglobin in any 24-week window.

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For the model, persistence in PNH is less about stopping treatment and more about moving between treatments. The number to forecast is how many patients on a C5 inhibitor stay on it, add a medicine, or switch class.

Where does this approach fall short?

The PNH chain is better measured than most, and it still has weak links.

• The UK counts do not share a definition. The population estimate counts detectable PNH cells; the service counts referred patients. We show both and do not divide one by the other.
• The Registry is not a census. It enrols patients at participating centres, and its treated share depends on when the data were cut.
• Single-centre outcome studies travel badly. The Leeds and Essen results come from expert centres. Outcomes in less specialised settings may differ.
• The newest medicines have little real-world data yet. Switching rates for the 2023 and 2024 approvals have to be assumed, then updated.

Key takeaways

• Define PNH before counting it. Only 8% of people with detectable PNH cells in Yorkshire had classical PNH.
• The UK has a counted specialist-care step. 1,146 patients in the national service in 2024–25.
• Treatment is the minority. 439 of 1,146 (38%) were on NHS-funded complement inhibition.
• Clone size drives eligibility. High disease activity rose from 14% to 77% between the smallest and largest clones.
• Persistence means switching. 63% of patients on eculizumab in one centre needed transfusions at some point.

Frequently asked questions

Why is the treated share of PNH patients so low?

Most people with detectable PNH cells have aplastic anaemia with a small clone, and are monitored rather than treated. Treatment is mainly started for haemolysis or thrombosis.

Can the UK numbers be used for other countries?

The structure can, the counts cannot. Without a single national service, the specialist-care step has to be built from other sources in each market.

Which step moves fastest?

The treated step, by medicine. Five new PNH medicines and two biosimilars have reached the US market since 2018.

Where do the numbers come from?

Population studies, registries, the national service’s own report and regulator records, each checked at the source. We do not use market-research estimates as sources.

Get started

• PNH patient flow model on AXLRx: https://axlrx.ai/pnh/patient-flow-model/
• PNH patient flow, UK: https://axlrx.ai/pnh/uk/patient-flow-model/
• PNH patient flow, France: https://axlrx.ai/pnh/france/patient-flow-model/
• All PNH analysis on AXLRx: https://axlrx.ai/pnh/
• Commission a patient flow model for your asset: https://axlrx.ai/commission/

Related posts

• How do you build a patient flow model for a rare disease? https://medium.com/@sales.moatrx/how-do-you-build-a-patient-flow-model-for-a-rare-disease-ecf4d81a26c9
• How do you forecast a rare disease when most patients are undiagnosed? https://medium.com/@sales.moatrx/how-do-you-forecast-a-rare-disease-when-most-patients-are-undiagnosed-46703ae45b2f
• PNH competitive intelligence on AXLRx: https://axlrx.ai/pnh/competitive-intelligence/

Part of The Rare-Disease Forecasting Series (2026): https://axlrx.ai/blog/rare-disease-commercial-analytics-attractive-hard-to-analyze/

Sources

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2. National PNH Service (Leeds and King’s College Hospital), annual report 2024–25. https://pnhserviceuk.co.uk/healthcare-professionals/annual-report/
3. Ueda Y et al. Diagnostic delay and clinical outcomes of paroxysmal nocturnal hemoglobinuria: Japanese claims data. Int J Hematol 2026. https://doi.org/10.1007/s12185-026-04260-9
4. Schrezenmeier H et al. Baseline clinical characteristics and disease burden in PNH: updated analysis from the International PNH Registry. Ann Hematol 2020. https://doi.org/10.1007/s00277-020-04052-z
5. Dingli D et al. Relationship of PNH granulocyte clone size to disease burden and risk of major vascular events. Ann Hematol 2023. https://doi.org/10.1007/s00277-023-05269-4
6. Schrezenmeier H et al. Baseline characteristics and disease burden in patients in the International PNH Registry. Haematologica 2014. https://doi.org/10.3324/haematol.2013.093161
7. Kelly RJ et al. Long-term treatment with eculizumab in PNH: sustained efficacy and improved survival. Blood 2011. https://doi.org/10.1182/blood-2011-02-333997
8. Versmold K et al. Long-term outcomes of patients with PNH treated with eculizumab in a real-world setting. Eur J Haematol 2023. https://doi.org/10.1111/ejh.13970
9. US Food and Drug Administration, Drugs@FDA approval records for Soliris, Ultomiris, Empaveli, Fabhalta, Voydeya, Piasky, Bkemv and Epysqli.
10. Kelly RJ et al. Treatment outcomes of complement protein C5 inhibition in 509 UK patients with PNH. Blood 2024. https://doi.org/10.1182/blood.2023021762
11. Pike A et al. COVID-19 infection in patients on anti-complement therapy: the Leeds National PNH service experience. Br J Haematol 2020. https://doi.org/10.1111/bjh.17097
12. Bektas M et al. Paroxysmal nocturnal hemoglobinuria: patient journey and burden of disease. J Manag Care Spec Pharm 2020 (funded by Apellis). https://doi.org/10.18553/jmcp.2020.26.12-b.s8