Table 2.

Time thresholds for mothership to be the preferred strategy.

LVO Screening methods	Probability of LVO	Ideal time metrics		Real-world time metrics

		Scene to PSC arrival time (min)^*	Additional transport time to CSC (min)	Scene to PSC arrival time (min)^*	Additional transport time to CSC (min)
LVO prevalence = 0.0487
Screened Negative²⁹^†	0.02	<60	<1	<40	<23
Screened Negative²⁹^†		>100	<2	>70	<28
No Screening¹⁸	0.0487	<60	<2	<40	<28
No Screening¹⁸		>100	<5	>70	<39
Screened Positive^‡
High sensitivity/ Low specificity³⁰	0.07	<60	<3	<40	<32
High sensitivity/ Low specificity³⁰		>100	<8	>70	<46
Moderate sensitivity/ Moderate specificity²⁹	0.18	<60	<9	<20	<50
Moderate sensitivity/ Moderate specificity²⁹		>100	<18	>70	<83
Low sensitivity/ High specificity³¹	0.23	<60	<11	<20	<59
Low sensitivity/ High specificity³¹		>100	<23	>70	<99

LVO prevalence = 0.118
Screened Negative²⁹^†	0.06	<60	<3	<40	<30
Screened Negative²⁹^†		>100	<7	>70	<43
No Screening²	0.118	<60	<6	<40	<40
No Screening²		>100	<12	>70	<63
Screened Positive^‡
High sensitivity/ Low specificity³⁰	0.16	<60	<8	<40	<47
High sensitivity/ Low specificity³⁰		>100	<16	>70	<77
Moderate sensitivity/ Moderate specificity²⁹	0.36	<60	<18	<20	<103
Moderate sensitivity/ Moderate specificity²⁹		>100	<33	>70	<135
Low sensitivity/ High specificity³¹	0.45	<60	<23	<20	<130
Low sensitivity/ High specificity³¹		>100	<39	>70	<158

LVO, Large vessel occlusion; PSC, primary stroke center; CSC, comprehensive stroke center.

The dichotomized time ranges presented for scene to PSC arrival time were generated from both individual sensitivity analyses and visual inspection of the two-way sensitivity analysis figures.

^†

Probability of LVO calculated from using a single scale with moderate sensitivity (0.63), moderate specificity (0.85).

^‡

We calculated positive predictive values across the full range of reported sensitivity/specificity, and chose to present 3 representative combinations: 1. high sensitivity (0.83), low specificity (0.40), and positive likelihood ratio (1.8); 2. moderate sensitivity (0.63), moderate specificity (0.85), and positive likelihood ratio (4.3); and 3. low sensitivity (0.30), high specificity (0.95), and positive likelihood ratio (6.0).