Assessment of the aggregate risk score to predict mortality after surgical biopsy for interstitial lung disease†

Abstract

Objectives: An aggregate risk score (range 0-6 points) for predicting mortality after surgical biopsy for interstitial lung disease (ILD) was recently developed from four independent variables: intensive care unit treatment (2 points), age >67 years (1.5 points), immunosuppression (1.5 points), open biopsy (1 point). In the development cohort, patients were grouped in four classes of aggregate score (A, B, C, D) showing incremental risk of death within 90 days from biopsy. We tested this mortality risk model in an independent cohort.

Methods: The aggregate risk score and the corresponding class of 90-day mortality risk was retrospectively determined in 151 consecutive patients undergoing biopsy for uncertain ILD at the Center for Thoracic Surgery, University of Insubria (Varese, Italy) in 1997-2012. We evaluated, by Spearman's ρ test, the correlation between aggregate risk score and mortality rate in the development cohort and in our cohort. Fisher's exact test was used for comparison of overall mortality rate between the two cohorts.

Results: The mortality rate correlation with risk score differed in our cohort (ρ = 0.127; P = 0.06) compared with the development cohort (ρ = 0.352; P < 0.0001). In our dataset mortality polarized: it was minimal in Classes A and B (2% and 0%, respectively), 33% in Classes C and D. This skewed mortality distribution was possibly contributed by significantly lower overall mortality rate in our cohort than in the development cohort (2.6% vs 10.6%; P = 0.0017). Despite the difference in mortality distribution, in our dataset, we confirmed that ILD patients with aggregate score >2 (Classes C and D) were at exceedingly high risk of postoperative mortality.

Conclusions: The aggregate score is a simple and useful risk score for ILD. Our dataset confirms that lung biopsy is reasonably safe in Class A and B patients while, in Class C and D patients, it is indicated only if histology would substantially change management and prognosis.

Keywords: Aggregate risk score; Interstitial lung disease; Mortality; Surgical lung biopsy.