The following options are currently available for testing SARS-CoV-2:
- determination of viral nucleic acid (RNA) by PCR method;
- detection of viral antigens (proteins);
- detection of antiviral antibodies in the body.
Detection of viral RNA is used in Estonia and worldwide for the detection of coronavirus and, in case of a positive result, for the primary diagnosis of COVID-19.
The main benefit of the test is its ability to detect the presence of the virus at an early stage, which helps to implement quarantine immediately. Another advantage is the reliability of results: the test is very specific and highly sensitive — it detects even a small amount of the virus. Viral RNA can be detected using the so-called traditional real-time PCR (Polymerase chain reaction) method, which requires specific equipment, specially trained laboratory technicians and a tailored laboratory process. A similar method is used in the laboratories of the Estonian Health Board, SYNLAB and several hospitals, and it allows for the carrying out of relatively large-scale tests.
In hospital admission and intensive care units, it is also useful to detect viral RNA with POCT (Point-of-care testing) devices, which do not require dedicated personnel. Although these devices have lower capacity, the results are received faster, making this method especially beneficial for people arriving at the emergency rooms.
Detection of viral RNA is the method of choice for the primary diagnosis of COVID-19 both by the World Health Organization (WHO) and the European Centre for Disease Prevention and Control (ECDC) (see Sources 1, 2).
RAPID ANTIGEN TESTS
The (rapid) antigen tests currently available have generally lower analytical sensitivity compared to RNA detection, giving many false-negative results in patients with low levels of virus in the body. According to the recommendations of the WHO’s Laboratory Testing Strategy for coronavirus SARS-CoV-2, antigen tests should not be treated as an alternative to PCR testing.
The coronavirus SARS-CoV-2 antibody tests measure the body’s response to the virus, which takes some time to develop. Studies indicate that antibodies to this type of coronavirus develop over 10 days after the onset of symptoms (see Source 2). As the patient is at high risk of infection throughout this time, it is clear that the antibody test is not suitable for the early diagnosis of the disease and for determining the person’s need to quarantine. However, both the WHO and the ECDC have recognised that antibody tests may be required for subsequent epidemiological studies. The sample used for antibody analysis is blood.
In conclusion, with today’s knowledge and technology, the most reliable method for detecting coronavirus is the SARS-CoV-2 RNA test, which is usually performed from a nasopharyngeal swab sample. The detection of the virus by PCR method from other materials (e.g. throat swab) is in the testing phase worldwide.
Virus vs. disease? Check out the correct terminology HERE.