Accuracy of certification of deaths due to asthma. A national study

In a two-year study of asthma mortality in New Zealand conducted between August 1981 and July 1983, the certified cause of death and its subsequent statistical coding was compared with the opinion of a panel of respiratory physicians who had made detailed enquiry into the medical history and circumstances surrounding the death of each patient. When the panel's opinion was taken as the reference standard, the national health statistics overestimated asthma mortality for all age groups by 26.0%. For patients aged 15-64 years, the net overestimate was 12.9%, no greater than that found in a similar study in this age group in the United Kingdom. Failure of certifying doctors and coroners to follow appropriate procedures for identification of the primary condition leading to death, or misdiagnosis of other lung disease as asthma, accounted for most inaccuracies in certification. In patients under age 35 years, certification and statistical coding of asthma death was considered accurate in 97.8% of all cases, but accuracy declined with increasing age. The high New Zealand asthma mortality rate, especially in young people, could not be explained by inaccuracies in death certification or statistical coding.