摘要：Detection of idiopathic interstitial pneumonias (IIPs) on chest X-ray is difficult for non-specialist physicians, especially in patients with mild IIPs. The current study aimed to evaluate the usefulness of a simple method for detecting IIPs by measuring vertical lung length (VLL) in chest X-rays to quantify decreased lung volume. A total of 280 consecutive patients with IIPs were randomly allocated to exploratory and validation cohorts, and 140 controls were selected for each cohort by propensity score-matching. Upper (
uVLL; from apex to tracheal carina), lower (
lVLL; from carina to costophrenic angle), and total VLL (
tVLL; from apex to costophrenic angle), and the
l/
uVLL ratio were measured on chest X-rays. Patients in the exploratory cohort had significantly decreased
uVLL,
lVLL,
tVLL, and
l/
uVLL ratio compared with controls (all
p < 0.001). Receiver operating characteristic curve analyses demonstrated that
lVLL (area under the curve [AUC
