COVID-19 testing

Molecular tests, primarily reverse transcription polymerase chain reaction (RT-PCR), detect the virus's genetic material and are considered the gold standard for diagnosing active infection.¹ These tests are highly sensitive and specific, but require laboratory equipment and trained personnel, leading to longer turnaround times. Sample types include nasopharyngeal swabs, saliva, and anterior nares swabs. The development of rapid molecular tests, such as isothermal amplification methods, has expanded access to molecular testing in point-of-care settings.

Antigen tests detect viral proteins and are typically used as rapid diagnostic tests, providing results in 15–30 minutes. They are less sensitive than PCR, especially in asymptomatic cases, but are valuable for frequent screening and outbreak control. The World Health Organization recommends their use in community settings where PCR is unavailable. Antigen tests are most reliable during the early phase of infection when viral load is high.

Antibody (serology) tests detect past infection or vaccination by measuring IgG, IgM, or IgA antibodies in blood.² They are not used for diagnosing acute infection because antibodies take days to weeks to develop. Seroprevalence surveys have used these tests to estimate population-level exposure. However, antibody levels wane over time, and cross-reactivity with other coronaviruses can cause false positives.

Beyond the main test types, several niche aspects exist. Pooled testing, where multiple samples are combined and tested together, was widely used to increase throughput and reduce costs during surges. Saliva-based tests gained popularity due to non-invasive collection and reduced PPE use. The first COVID-19 test was developed by the WHO's network of laboratories in January 2020, and the first US test was developed by the CDC. Additionally, at-home rapid tests became a key tool for self-screening, with regulatory approvals in many countries. The accuracy of tests can be affected by viral variants, leading to ongoing evaluation and updates.

RT-PCR

Reverse transcription polymerase chain reaction, a molecular technique that amplifies viral RNA to detect infection.

Antigen

A viral protein that triggers an immune response; detected in rapid diagnostic tests.

Antibody

A protein produced by the immune system in response to infection or vaccination.