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. 2023 Sep;17(9):831-840.
doi: 10.1111/crj.13564. Epub 2022 Nov 27.

External validation of the GAP model in Chinese patients with idiopathic pulmonary fibrosis

Xinran Zhang  1 , Yanhong Ren  2 , Bingbing Xie  2 , Shiyao Wang  2 , Jing Geng  2 , Xuan He  2 , Dingyuan Jiang  2 , Jiarui He  2 , Sa Luo  2 , Xin Wang  2   3 , Dingyun Song  2 , Mingming Fan  2   4 , Huaping Dai  2
Affiliations

External validation of the GAP model in Chinese patients with idiopathic pulmonary fibrosis

Xinran Zhang et al. Clin Respir J. 2023 Sep.

Abstract

Introduction: The GAP model was widely used as a simple risk "screening" method for patients with idiopathic pulmonary fibrosis (IPF).

Objectives: We sought to validate the GAP model in Chinese patients with IPF to evaluate whether it can accurately predict the risk for mortality.

Methods: A total of 212 patients with IPF diagnosed at China-Japan Friendship Hospital from 2015 to 2019 were enrolled. The latest follow-up ended in September 2022. Cumulative mortality of each GAP stage was calculated and compared based on Fine-Gray models for survival, and lung transplantation was treated as a competing risk. The performance of the model was evaluated in terms of both discrimination and calibration.

Results: The cumulative mortality in patients with GAP stage III was significantly higher than that in those with GAP stage I or II (Gray's test p < 0.0001). The Harrell c-index for the GAP calculator was 0.736 (95% CI: 0.667-0.864). The discrimination for the GAP staging system were similar with that for the GAP calculator. The GAP model overestimated the mortality rate at 1- and 2-year in patients classified as GAP stage I (6.90% vs. 1.77% for 1-year, 14.20% vs. 6.78% for 2-year).

Conclusions: Our findings indicated that the GAP model overestimated the mortality rate in mild group.

Keywords: GAP model; external validation; idiopathic pulmonary fibrosis; prognosis.

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Conflict of interest statement

No potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Figures

FIGURE 1
FIGURE 1
The cumulative mortality of patients with IPF by the GAP staging system. Blue represents patient with GAP stage I. Red represents patient with GAP stage II. Green represents patient with GAP stage III.
FIGURE 2
FIGURE 2
Calibration plots of the GAP calculator in patients with IPF. The x‐axis shows the predicted probability of death by the GAP calculator, and the y‐axis shows the observed probability of death. The solid line represents perfect agreement between predicted and observed risks, and the dashed line represents ±10% differences between them.
FIGURE 3
FIGURE 3
Calibration plots of the GAP staging system in patients with IPF. The x‐axis shows the predicted probability of death by the GAP staging system, and the y‐axis shows the observed probability of death. The solid line represents perfect agreement between predicted and observed risks, and the dashed line represents±10% differences between them.
FIGURE 4
FIGURE 4
The cumulative mortality of patients with IPF by the modified GAP staging system. Blue represents patient with the modified GAP stage I. Red represents patient with the modified GAP stage II. Green represents patient with the modified GAP stage III.
See this image and copyright information in PMC

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