Table 3. Comparison of cut-off points and ROC curves between ROX index at initiation and after 1 hour of HFNC.

Index/ score	Cut-off point	Sensitivity at cut-off point	Specificity at cut-off point	Positive predictive value at cut-off point	Negative predictive value at cut-off point	Positive likelihood ratio at cut-off point	Negative likelihood ratio at cut-off point	AUC (95% CI)
All AHRF patients
ROX	6.93 (Youden)	0.52	0.69	0.51	0.7	1.67	0.7	0.62 (0.57–0.68)
	5.18	0.31	0.8	0.49	0.65	1.55	0.86
	3.84	0.16	0.91	0.52	0.64	1.78	0.92
ROX at 1h	7.96 (Youden)	0.59	0.65	0.51	0.72	1.69	0.63	0.65 (0.60–0.71)
	6.46	0.37	0.8	0.53	0.67	1.85	0.79
	4.94	0.22	0.91	0.6	0.66	2.44	0.86
AHRF patients with pneumonia only
ROX	6.56 (Youden)	0.59	0.67	0.52	0.73	1.79	0.61	0.65 (0.57–0.72)
	4.58	0.41	0.81	0.57	0.69	2.16	0.73
	3.62	0.21	0.91	0.59	0.65	2.33	0.87
ROX at 1h	7.18 (Youden)	0.65	0.68	0.55	0.76	2.03	0.51	0.71 (0.64–0.79)
	6.06	0.51	0.8	0.61	0.73	2.55	0.61
	4.64	0.33	0.91	0.69	0.69	3.67	0.74
AHRF patients not due to non-pneumonia conditions
ROX	7.59 (Youden)	0.53	0.72	0.54	0.71	1.89	0.65	0.62 (0.55–0.69)
	6.24	0.33	0.80	0.51	0.66	1.65	0.84
	4.36	0.14	0.90	0.46	0.63	1.40	0.96
ROX at 1h	11.54 (Youden)	0.82	0.42	0.47	0.79	1.41	0.43	0.63 (0.56–0.70)
	6.89	0.34	0.80	0.51	0.66	1.79	0.83
	5.44	0.13	0.91	0.45	0.63	1.44	0.96

AUC: Area under the receiver operating characteristic curve.

CI: Confidence interval.