Rare Disease · In-Market · Updated August 2026
In PNH the market is not sized by prevalence. It is sized by how many patients have had the flow-cytometry test that confirms the diagnosis, and most have not.
PNH is an acquired clonal disorder whose presenting features - fatigue, haemoglobinuria and thrombosis - mimic far more common conditions. Confirmation requires high-sensitivity flow cytometry for GPI-anchor-deficient cells, a test that sits outside the standard anaemia and thrombosis work-up. Most patients are therefore diagnosed only after an unexplained haemolytic or thrombotic event routes them to haematology, often years after symptom onset. The referral-and-testing pathway, not efficacy or price, is the rate-limiting step in this market.
Treatment has divided into two mechanisms. Intravenous anti-C5 antibodies have held the majority of diagnosed patients since the class was established, and an oral Factor B inhibitor has since opened a switch that the class cannot answer on convenience alone. The live commercial opportunity is not the market at large but a specific cohort: patients with extravascular haemolysis who remain anaemic on intravenous anti-C5 therapy. Modelled as a subpopulation conversion, that cohort behaves nothing like a share-of-market contest, and an analogue curve borrowed from a larger indication will overstate uptake substantially.
The payer case does not transfer between markets. In the United States it turns on whether an agent routes through the medical or the pharmacy benefit, on prior-authorisation criteria that are still forming, and on the orphan-drug exclusion that shields the class from Medicare negotiation. In the United Kingdom it runs through the ultra-rare appraisal route with its own threshold. In the Gulf the gate is registration and payer infrastructure, which lag both.
AXLRx PNH reports build that funnel end to end, size the switch cohort with testing rate as an explicit sensitivity, and construct the value case market by market. Each report is a sample output of the AXLRx commercial consulting engine, and the same analysis can be commissioned for your asset and market.
For the wider context, see orphan drug approvals in numbers: FDA and EMA orphan approvals counted by year, condition and sponsor.
Paroxysmal nocturnal hemoglobinuria (PNH) is an ultra-rare acquired clonal hematopoietic stem-cell disorder, with an estimated ~18,000 diagnosed patients in the US. The true number is uncertain: PNH is frequently missed because its hallmark features (fatigue, hemoglobinuria, and thrombosis) mimic far more common conditions, and confirmation requires a flow-cytometry test that is not routinely ordered. The gap between the epidemiological and the diagnosed population is the single most important number to get right in PNH commercial work.
PNH is confirmed by high-sensitivity flow cytometry detecting GPI-anchor-deficient blood cells. Because the presenting symptoms are non-specific and the test is not part of a standard anemia or thrombosis work-up, most patients are diagnosed only after an unexplained hemolytic or thrombotic event routes them to hematology, often years after symptom onset. For a commercial team, the referral-and-testing pathway (who orders flow cytometry, and when) is the true rate-limiting step, upstream of any question about efficacy or price.
Four agents are approved: eculizumab (Soliris, AstraZeneca) and ravulizumab (Ultomiris, AstraZeneca), both intravenous anti-C5 monoclonal antibodies; iptacopan (Fabhalta, Novartis), the first oral Factor B inhibitor, approved in 2023; and crovalimab (Piasky, Roche/Chugai), a subcutaneous anti-C5 antibody approved in 2024. The anti-C5 class has historically covered roughly 60-70% of diagnosed patients, and the commercial contest now centres on the oral switch dynamic that iptacopan introduced.
Not from prevalence. In an ultra-rare, diagnosis-limited disease the defensible number is built bottom-up as a funnel: diagnosed prevalence, then the treated pool, then the specific subpopulation your asset targets, in PNH the ~1,000 patients with extravascular hemolysis (EVH) who remain anemic on IV anti-C5 and are the oral switch candidates. The variable that moves this number most is not efficacy but flow-cytometry testing penetration and referral rate. Any PNH forecast that assumes full diagnosis overstates the near-term addressable pool, and the sizing has to be shown as a sensitivity on the testing rate, not a single point estimate.
Model it as a subpopulation conversion, not a share grab. The realistic near-term opportunity is the EVH-dominant cohort transfusing despite IV C5 therapy, so the forecast is built patient-by-patient off that funnel and off the timing of payer step-edit and prior-authorization criteria, which form gradually and gate the switch. Because the anti-C5 price anchor is shielded from IRA Medicare negotiation by the orphan-drug exclusion, oral entry is additive to a stable-priced class rather than a price war. Anchoring an oral-switch forecast on a large-indication analog curve consistently overstates uptake in PNH.
Geo by geo, because the frameworks do not transfer. In the US, the case is built around Part B (IV buy-and-bill) versus Part D (oral) routing, the forming PA and step-edit criteria, and the orphan-drug IRA exclusion that keeps the class anchor intact; ICER's value benchmark (~$156K-157K) is the reference point to argue against. In the UK, PNH agents run through NICE's Highly Specialised Technologies route with its distinct cost thresholds. In the GCC, the gate is SFDA registration and payer infrastructure, which typically lag US and EU access. The value story rests on the transfusion-burden offset in a defined subpopulation, not a whole-population claim.
Because in PNH the addressable market is defined by the patient-identification funnel, not by prevalence, and the live opportunity is a specific subpopulation rather than the market at large. Analog curves borrowed from larger indications assume a findable, fully-diagnosed population and a broad treated pool, both false here. The disciplined approach is a bottom-up model where diagnosis rate, testing penetration, and subpopulation size are the explicit levers, each defensible in a forecast review. In rare disease the funnel is the strategy; the label is not.
The analysis behind the questions above: a bottom-up patient-flow model from diagnosed prevalence to the EVH switch cohort with testing-rate sensitivities; competitive intelligence on the forming PA and step-edit dynamics; a payer and HTA value case built market by market for the US, UK, and GCC; KOL and treatment-centre mapping; and pricing analysis against the ICER benchmark. Each is scoped to your asset and its target subpopulation, delivered as a sourced brief, an editable model, or an executive readout.