The Italian National Rare Diseases Registry: a model of comparison and integration with Hospital Discharge Data.

Background Italy has been the first country at European level to implement a population-based public health registry dedicated to rare diseases. This study describes the current situation of the Italian National Rare Diseases Registry (NRDR) and compares its data with those from the National Hospital Discharge Database (HDD). Methods Three rare diseases were analysed: Huntington disease (HD), Hereditary Haemorragic Telangiectasia (HHT) and Prader-Willi Syndrome (PWS), selected for their different characteristics. The two sources (NRDR and HDD) were linked: incidence rate ratio (IRR), sensitivity and predictive positive value (PPV) were calculated. Results Incidence rates from NRDR and from HDD were compared by age groups, and IRR calculated: 1.08 for HD, 1.41 for HHT, 1.21 for PSW. For HD, sensitivity was 0.52 and PPV 0.48; for HHT sensitivity was 0.71 and PPV 0.52; for PWS the sensitivity was 0.71 and PPV 0.58. We found a strong regional variability in the results. Conclusions The integrated use of the two sources helps tracking those cases that are not captured by the Registry; further, it is a precious tool to accurately describe clinical histories of rare disease affected individuals, in terms of concomitant pathologies and medical procedures performed during hospitalization.