Idiopathic pulmonary fibrosis: CT and risk of death

Purpose: To investigate the prognostic value of quantitative computed tomographic (CT) scoring for the extent of fibrosis or emphysema in the context of a clinical model that includes the gender, age, and physiology (GAP model) of the patient.

Materials and Methods: Study cohorts were approved by local institutional review boards, and all patients provided written consent. This was a retrospective cohort study that included 348 patients (246 men, 102 women; mean age, 69 years±9) with idiopathic pulmonary fibrosis from two institutions. Fibrosis and emphysema visual scores were independently determined by two radiologists. Models were based on competing risks regression for death and were evaluated by using the C index and reclassification improvement.

Results: The CT-GAP model (a modification of the original GAP model that replaces diffusion capacity of carbon monoxide with CT fibrosis score) had accuracy comparable to that of the original GAP model, with a C index of 70.3 (95% confidence interval: 66.4, 74.0); difference in C index compared with the GAP model of 20.4 (95% confidence interval: 22.2, 3.4). The performance of the original GAP model did not change significantly with the simple addition of fibrosis score, with a change in C index of 0.0 (95% confidence interval: 21.8, 0.5) or of emphysema score, with a change in C index of 0.0 [95% confidence interval: 21.3, 0.4]).

Conclusion: CT fibrosis score can replace diffusion capacity of carbon monoxide test results in a modified GAP model (the CTGAP model) with comparable performance. This may be a useful alternative model in situations where CT scoring is more reliable and available than diffusion capacity of carbon monoxide.