A validation of the National Early Warning Score (NEWS) to predict outcome in patients with COPD exacerbation

Background: The National Early Warning Score (NEWS), proposed as a standardised track and trigger system, may perform less well in acute COPD exacerbation (AECOPD). This study externally validated NEWS and modifications (CREWS and Salford-NEWS) in AECOPD. Methods: An observational cohort study (2012-2014, two UK acute medical units [AMUs]), compared AECOPD (2,361 admissions, 942 individuals, ICD-10 J40-44 codes) with AMU patients (37,109 admissions, 20,415 individuals). Outcome: in-hospital mortality prediction by admission NEWS, CREWS and Salford-NEWS assessed by discrimination (area under receiver operating characteristic curves [AUCs]) and calibration (plots and Hosmer-Lemeshow [H-L] goodness-of-fit).Results: Median admission NEWS in AECOPD was 4 (IQR 2-6) vs 1 (0-3) for AMU (p=<0.001), despite mortality 4.5% in both. AECOPD AUCs were: NEWS 0.74 (95% confidence intervals 0.66 to 0.82), CREWS 0.72 (0.63 to 0.80) and Salford-NEWS 0.62 (0.53 to 0.70). AMU NEWS AUC was 0.77 (0.75 to 0.78). At threshold NEWS=5 for AECOPD (44% of admissions), positive predictive value (PPV) of death was 8% (5 to 11) and negative predictive value (NPV) 98% (97 to 99) vs AMU patients PPV 17% (16 to 19) and NPV 97% (97 to 97). For NEWS in AECOPD H-L P-value =0.202.Conclusions: This first validation of the NEWS in AECOPD found modest discrimination to predict mortality. Lower specificity of NEWS in AECOPD patients vs other AMU patients reflects acute and chronic respiratory physiological disturbance (including hypoxia), with resultant low PPV at NEWS=5. CREWS and Salford-NEWS, adjusting for chronic hypoxia, increased specificity and PPV but there was no gain in discrimination