Standardised mortality rates in females and males with COPD and asthma

Mortality studies of males and females with chronic obstructive pulmonary disease (COPD) and asthma have suggested that females have a poorer prognosis than males, but the results are either not unanimous or based on poorly characterised patients. The current study analysed the mortality of 279 asthma patients and 869 COPD patients, who were seeking pension due to disability, and compared mortality rates with expected rates derived from the general population. The mean follow-up period was 13.3 yrs (range 2.5-22.4 yrs) during which time 96 (34.4%) and 671 (77.2%) deaths were identified among asthma and COPD patients, respectively. The average age at study entry was 46.8 and 56.6 yrs, and the average forced expiratory volume in one second (FEV1) was 68.8 and 44.1 % predicted in the two diagnostic groups. After adjustment for predictors of survival (age, FEV1 % predicted, chronic bronchitis, body mass index, smoking status, oral prednisolone, ischaemic heart disease, and cor pulmonale), the relative risk of death was 1.21 (95% confidence interval: 0.77-1.89) and 0.98 (0.83-1.16) in females compared with males, in asthma and COPD patients, respectively. The standardised mortality rate (SMR) for males was 1.54 (1.10-2.09) and 2.7 (2.5-3.0), and for females 1.91 (1.44-2.49) and 4.8 (4.2-5.4), in asthma and COPD patients, respectively. Direct comparison of the SMR of males and females showed that females had higher mortality than males, with a rate ratio of 1.24 (0.82-1.84) and 1.8 (1.5-2.0), in asthma and COPD patients, respectively. Poisson regression analysis with control for the confounders did not change this result. Females and males with the same level of obstructive lung disease appear to have the same level of mortality. However, using standardised mortality rates, females have a higher mortality than males, suggesting that the protective effect of being female is lost in chronic obstructive pulmonary disease patients.