Panel a: Scenario 1 – Low Pretest Probability (LFA) | ||||
---|---|---|---|---|

Dx | No Dx | PPV | NPV | |

Prevalence 0.1%, Sn 90, Sp 95 | ||||

(+) | 9 | 500 | 1.8% | 99.9% |

(-) | 1 | 9490 | ||

Prevalence 0.2%, Sn 90, Sp 95 | ||||

(+) | 18 | 499 | 3.5% | 100.0% |

(-) | 2 | 9481 |

Panel b: Scenario 2 – Intermediate Pretest Probability (RT-PCR Initially Negative) | ||||
---|---|---|---|---|

Dx | No Dx | PPV | NPV | |

Prevalence 40%, Sn 85%, Sp 95% | ||||

(+) | 34 | 3 | 91.9% | 90.5% |

(-) | 6 | 57 | ||

Prevalence 60%, Sn 85%, Sp 95% | ||||

(+) | 51 | 2 | 96.2% | 80.9% |

(-) | 9 | 38 |

Panel c: Scenario 3 – High Pretest Probability (RT-PCR) | ||||
---|---|---|---|---|

Dx | No Dx | PPV | NPV | |

Prevalence 80%, Sn 90%, Sp 95% | ||||

(+) | 72 | 1 | 98.6% | 70.4% |

(-) | 8 | 19 | ||

Prevalence 80%, Sn 80%, Sp 95% | ||||

(+) | 64 | 1 | 98.4% | 54.3% |

(-) | 16 | 19 |

LFA, lateral flow assay; RT-PCR, real-time polymerase chain reaction.

*These tables describe the distribution of 10,000 (panel a) or 100 patients (panels b and c) with and without the disease (COVID-19) compared to with positive and negative test results.

^{†}Sensitivity (Sn), the proportion of infected individuals who test positive.^{‡}specificity (Sp), the proportion of uninfected individuals who test negative.^{§}Dx, patient has disease; no Dx, patient does not have disease.^{||}(+), test result is positive; (-), test result is negative.^{¶}Positive predictive value (PPV), the probability that a positive test result actually means one has COVID-19.^{¶¶}Negative predictive value (NPV), the probability that a negative test result actually means one does not have COVID-19.