Idiopathic pulmonary fibrosis: survival in population based and hospital based cohorts

To ascertain whether findings from hospital based clinical series can be extended to patients with idiopathic pulmonary fibrosis (IPF) in the general population, the survival of patients with IPF in a population based registry was compared with that of a cohort of patients with IPF treated at major referral hospitals and the factors influencing survival in the population based registry were identified.

The survival of 209 patients with IPF from the New Mexico Interstitial Lung Disease Registry and a cohort of 248 patients with IPF who were participating in a multicentre case-control study was compared. The determinants of survival for the patients from the Registry were determined using life table and proportional hazard modelling methods.

The median survival times of patients with IPF in the Registry and case-control cohorts were similar (4.2 years and 4.1 years, respectively), although the average age at diagnosis of the Registry patients was greater (71.7 years versus 60.6 years, p < 0.01). After adjusting for differences in age, sex, and ethnicity, the death rate within six months of diagnosis was found to be greater in the Registry patients (relative hazard (RH) 6.32, 95% CI 2.19 to 18.22) but more than 18 months after diagnosis the death rate was less (RH 0.35, 95% CI 0.19 to 0.66) than in the patients in the case-control study. Factors associated with poorer prognosis in the Registry included advanced age, severe radiographic abnormalities, severe reduction in forced vital capacity, and a history of corticosteroid treatment.

The adjusted survival of patients with IPF in the general population is different from that of hospital referrals which suggests that selection biases affect the survival experience of referral hospitals.