The diagnostic accuracy of Rapid Antigen Tests (RAT) has been widely studied in various applications and in diverse populations.
Sensitivity, in the order of 75% in pooled estimates, is significantly influenced by the presence or absence of symptoms, viral load, and the timing of sampling relative to the onset of symptoms.
Specificity, in the order of 99% in pooled estimates, is consistently high across tests, populations, and sampling methods.
Post-test probability of being an infectious case following a positive test is highest in individuals with a high pre-test probability (population prevalence > 5%), such as those with COVID-19 symptoms, and those in settings with a high level of community transmission. Here, the positive predictive value is in the order of 95%. However, when used in settings with a lower pre-test probability (population prevalence < 0.5%), as in screening asymptomatic individuals, the positive predictive value is considerably reduced, as low as 25%.
Post-test probability of being an infectious case following a negative test is less than 1% (negative predictive value > 99%) in all settings except those with the highest levels of community transmission.
Badea, A; Reeder, B; Groot, G; Muhajarine, N; Minion, J; Miller, L; Howell-Spooner, B. In real world settings, what is the validity of Rapid Antigen Tests (RATs) in identifying SARS-CoV-2 and how well do they predict disease? 2022 Jan 12, Document no.: EOC211201 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2022. 15 p. (CEST rapid review report).
The overall ‘clinical’ false negative rate (1 – sensitivity) of rt-PCR in the detection of SAR-CoV-2 in the respiratory tract is estimated to be 30%, although estimates vary from 3.5 – 50%. This rate is higher when the technique of clinical sampling is poor, higher in nasopharyngeal and oral swabs than lower respiratory tract secretions, and higher early in the course of disease (prior to symptom development) and following the first week of symptoms.
The performance of the rt-PCR test can be maximized by:
1. Timing and collecting specimens in the optimal manner
2. Applying the test in those individuals with a high pre-test probability of having COVID-19; this includes individuals living in communities with a high prevalence of disease, those with an epidemiological history linking them to a confirmed case, and those with symptoms associated with COVID-19, potentially identified with the aid of a clinical prediction rule
3. Serial testing with a repeat rt-PCR test after a specific interval such as 24-48 hours
4. In the clinical setting, the additional assessment of blood biomarkers, IgM/IgG serology and chest CT scan
These considerations apply to the decision to conduct initial rt-PCR testing as well as to the decision to re-test individuals with an initial negative result.
Badea, A; Reeder, B; Young, C; Dalidowicz, M; Miller, L. What factors can be used to identify negative PCR tests that are ‘false negatives’? 2020 May 25; Document no.: EOC052101 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2020. 12 p. (CEST rapid review report)