12th Congress of the European Hematology ... - Haematologica

tified with the current protocol. Summary. we identified abnormalities
suggestive of previous subclinical thromboses in 6 of 10 hemolytic PNH
patients by high-resolution MR imaging, including in patients on primary
prophylaxis with warfarin. Effective prevention of thrombosis is
an important aspect of the therapy in PNH.
0067
THE INCIDENCE AND PREVALENCE OF PAROXYSMAL NOCTURNAL HEMOGLOBINURIA
(PNH) AND SURVIVAL OF PATIENTS IN YORKSHIRE
A. Hill, 1 P.J. Platts, 2 A. Smith, 2 S.J. Richards, 1 M.J. Cullen, 1 Q.A. Hill, 1
E. Roman, 2 P. Hillmen1 1 2 Leeds General Infirmary, LEEDS; University of York, YORK, United Kingdom
Background. Paroxysmal nocturnal hemoglobinuria (PNH) is an
acquired clonal stem cell disorder characterized by the expansion of a
population of blood cells deficient in glycosylphosphatidylinositol (GPI)
linked proteins. This results in the classical clinical features of intravascular
hemolysis and thrombosis. PNH is known to be a rare disorder, but
its incidence and prevalence have so far been poorly defined with very
few studies. Aims. To better define the incidence and prevalence of PNH.
Methods. Survival data was collected on all patients diagnosed with PNH
in the strategic health authorities of North and East Yorkshire, Northern
Lincolnshire and West Yorkshire between January 1991 and July 2006.
All patients were diagnosed by flow cytometry for GPI-linked antigens
on red cells and neutrophils at a single reference laboratory (HMDS).
Results. The population of the study region is 3,742,835 (based on the
2001 census of Britain). 76 PNH patients were diagnosed during this
time period giving an incidence of 0.13/100,000/year. Based on incidence
and survival rates, the estimated 15 year prevalence of PNH is 1.59 per
100,000 resulting in a predicted prevalence of 59 patients in the study
region. We have previously demonstrated that a neutrophil clone size
>50% is a predictor of increased thrombotic risk; the current study predicts
that 25% of patients will have >50% PNH neutrophil clone size,
43% with >10%, and 82% with >1%. Platelet count >100×10 9 /L has
been used as a criteria to consider primary prophylactic anticoagulation
in PNH patients with substantial hemolysis if the neutrophil clone size
is >50%. In the current study, the platelet count is >100×10 9 /L in 32%
of patients and