Chronic immune thrombocytopenia in Denmark, Sweden and Norway: The Nordic Country Patient Registry for Romiplostim

Background: Population-based cohorts of immune thrombocytopenia (ITP) are useful for understanding occurrence, clinical characteristics and long-term clinical course. This paper describes the content of the Nordic Country Patient Registry for Romiplostim (NCPRR) and provides prevalence and incidence estimates of chronic ITP (cITP). Methods: The NCPRR, a cohort study established in 2009, includes all adult (>= 18 years) patients in Denmark, Sweden and Norway with cITP (defined as ITP lasting > 12 months and platelet count < 100 x 10(9)/L), combining data from national health registries and medical records. The NCPRR currently includes prevalent cITP patients diagnosed before 2009 and incident cITP patients diagnosed during 2009-2016. The registry obtains clinical information for cITP patients, including comorbidities, treatments, laboratory values, and complete follow-up for various outcomes. Findings: The NCPRR currently includes 3831 patients with cITP (1258 prevalent; 2573 incident). In 2009, the prevalence of registered cITP was 10.0/100,000 (95%Cl:9 1-11.0) adult persons in Denmark and 10.7 100,000 (95% CI: 9.9-11.4) adults in Sweden. During 2009-2016, the incidence rates of cITP per 100,000 person-years were 2.8 (95%Cl: 2.6-3.0), 1.8 (95%Cl: 1.7-1.9) and 2.1 (95%CI: 1.9-2.2) in Denmark, Sweden and Norway, respectively. Fifty-eight percent of cITP patients were women. At NCPRR inclusion, 30.2% were aged >= 70 years, 23% had a platelet count <50 x 10(9)/L, 17.4% were splenectomized, 41% had prior ITP therapy, and 8.6% had severe comorbidity. Interpretation: The NCPRR provides population-based data on the epidemiology and characteristics of almost 4000 cITP patients and is a valuable resource for research. (C) 2019 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.