Interpreting COVID-19 Test Results in Clinical Settings: It Depends!

Article Figures & Data

Table 1.

Theoretical Explanation of Individual Motivation for Seeking a Test Based on the Health Belief Model⁸

Constructs	Definition	Application to testing motivation
Perceived Susceptibility	Belief about the likelihood of getting a disease or condition	Perception of COVID-19 being an issue in the individual’s geographic area
Perceived severity	Belief about the seriousness of contracting a condition or of leaving it untreated, including physical consequences and social consequences	Perception the individual is at risk for COVID-19 given age and other demographics
Perceived benefits	Beliefs about positive features or advantages of a recommended action to reduce threat	Perception that a test provides beneficial information or is a “treatment” unto itself
Perceived barriers	Beliefs about negative features or of a recommended action to reduce threat	Perception that test is not useful or painful to get
Cue to action	Internal or external markers stimulus	Media coverage of testing; knowing others who have been tested; getting sick
Self-efficacy	The conviction that one can successfully execute a behavior	Ability to go and get a test

Table 2.

Test Performance in Three Hypothetical Clinical Scenarios*

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.