Comparison of national mortality data with routinely collected health-care data to measure the occurrence of liver cirrhosis: an observational study

Abstract

BackgroundIncidence of liver cirrhosis is increasing faster than the four most common diagnosed cancers (breast, colon, lung, prostate) in the UK. Mortality rates are commonly used to estimate the occurrence of cirrhosis because no other monitoring system is available for cirrhosis, but this measure has methodological limitations; there is a time lag between diagnosis and mortality, and not everyone with cirrhosis dies directly from the disease. This study compared estimates of liver cirrhosis incidence in England with mortality rates based on similar definitions of disease, over the same period. MethodsThis population-based cohort study used data from the Clinical Practice Research Datalink (CPRD) and linked English Hospital Episode Statistics (HES) to establish the number of new cases of cirrhosis between 1998 and 2009, on the basis of diagnostic codes for cirrhosis, oesophageal varices, and portal hypertension. Similar codes were used to identify deaths due to liver cirrhosis in the Office for National Statistics death registry over the same period. Mortality rates were calculated by dividing the number of deaths due to cirrhosis by mid-year population. Incidence rates were determined by dividing the number of cases by the total number of person-years from the CPRD-HES population at risk. Poisson regression was used to establish rate ratios adjusted for age and sex. Ethics approval was obtained where necessary. Findings5118 adults with an incident diagnosis of cirrhosis were identified; crude incidence increased from 24·6 to 38·4 per 100 000 person-years from 1998 to 2009. This increase fitted a continuous model with an average yearly incidence rate ratio of 1·04 (95% CI 1·03–1·05), corresponding to a 50·6% increase over the 12 years. By contrast, mortality rates for cirrhosis were 6·0 and 5·9 per 100 000 person-years in 1998 and 2009, respectively, representing a decrease of 2·5% over time. InterpretationMortality rates underestimated liver cirrhosis incidence by at least four times between 1998 and 2009. Alternative sources of routinely collected data could be used to more accurately monitor the trends in this disease. The strength of this study is the comparison of two measures of disease occurrence over the same time period; the limitation is the validity of cause of death. FundingUniversity of Nottingham and Nottingham University Hospitals NHS Trust. The funder had no role in the study.