COVID-19 PCR Test: Molecular Diagnostic Testing for Active SARS-CoV-2 Infection

The COVID-19 PCR test is a molecular diagnostic test that detects genetic material (RNA) from the SARS-CoV-2 virus, which causes COVID-19. It is used to determine whether you have an active infection at the time your sample is collected, and it is considered the most accurate method for diagnosing a current infection, even in people who have no symptoms.

The SARS-CoV-2 Interferon Gamma Release Assay (IGRA) is a specialized blood test that measures how your T-cells respond to SARS-CoV-2, the virus that causes COVID-19. When T-cells have been previously exposed to the virus (either through infection or vaccination), they become 'sensitized' and will release interferon gamma when re-exposed to viral antigens in the laboratory. This test detects that immune response.

A healthcare provider collects a sample by gently inserting a soft swab into your nose or throat, often the area deep behind the nose. In some cases, a saliva sample may be collected instead. The sample is sent to a laboratory, where a technique called reverse transcription polymerase chain reaction (RT-PCR) detects viral genetic material. Results are typically available within 24 to 72 hours, depending on the laboratory.

A healthcare professional will draw a blood sample from a vein in your arm. The sample is then sent to a laboratory where it is mixed with SARS-CoV-2 antigens. If your T-cells have been previously exposed to the virus, they will recognize these antigens and release interferon gamma, which is then measured. The test includes a positive control (to ensure your T-cells can respond) and a negative control (to account for background interferon gamma levels).

A positive result means genetic material from SARS-CoV-2 was detected in your sample and you currently have COVID-19. You should follow your healthcare provider's guidance on isolation, treatment, and notifying close contacts. A negative result means the virus was not detected at the time of testing, but if you were tested very soon after exposure, viral levels may have been too low to detect, so repeat testing a few days later may be recommended. Always review your results with a healthcare provider, especially if symptoms continue.

Results are typically reported as positive, negative, or indeterminate. A positive result suggests that your T-cells have been sensitized to SARS-CoV-2, indicating either past infection or immune response from vaccination. A negative result means no detectable T-cell response was found. Indeterminate results may require retesting. Your healthcare provider will interpret these results in the context of your medical history and vaccination status.

The PCR test detects the virus itself and diagnoses an active infection, while an antibody (serology) test looks for proteins your immune system produced in response to a past infection or vaccination. Antibody tests cannot tell whether you currently have COVID-19, because antibodies can remain in your blood for weeks or months after the infection has resolved. If you have symptoms or a known exposure now, the PCR test is the appropriate choice.

This test measures cellular immunity (T-cell response), while antibody tests measure humoral immunity (B-cell produced antibodies). T-cell responses may persist longer than antibodies, potentially providing a longer-term view of immune protection. This test can be useful even if antibody levels have declined.