What tests to use for diagnosing COVID-19?

With the COVID-19 pandemic, nearly 200 different COVID-19 diagnostic tests (including so-called rapid tests) have appeared on the market in the last few months and the number of manufacturers and dealers is increasing day by day (source here). At the same time, the media is talking about lack of resources, including diagnostic tools. In this situation, both the medical professionals and citizens have a question – why these tests are not used and which ones to trust.

The following options are currently available for testing SARS-CoV-2:

  • Determination of viral nucleic acid (RNA);
  • Detection of viral antigen (proteins);
  • Detection of antiviral antibodies in the body.

 Detection of viral RNA is used in Estonia and worldwide for the primary diagnosis and detection of COVID-19. The benefit of the test is the ability to detect the presence of the virus at an early stage, which will help quarantine immediately. Another advantage is the high reliability of results. Virus RNA can be detected using the so-called classical 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 is possible to carry out relatively large-scale tests. In addition, viral RNA detection using point-of-care testing (POCT) devices, which do not require dedicated personnel and have lower throughput but are faster to respond to, is useful in hospital admissions and intensive care units. Detection of viral RNA is the only method currently accepted by both the World Health Organization (WHO) and the European Center for Disease Prevention and Control (ECDC) (sources here and here). The antigen (quick) tests provided have generally significantly lower sensitivity compared to RNA detection, giving many false negative results. It is estimated that using these could bring more harm than benefit – many infectious COVID-19 patients with false-negative results could end the quarantine. This means that, in addition to over-checking the few positives in the viral recovery phase, many negative results should be re-tested in order to get a correct answer. According to the recent recommendations of the WHO’s COVID-19 Laboratory Testing Strategy, antigen tests are currently not recommended for clinical diagnosis.

The COVID-19 antibody test measures body’s response to the virus, which takes a certain amount of time to develop. According to recent studies, antibodies to this coronavirus develop over 10 days after the onset of symptoms (https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30196-1/fulltext). As the patient is highly infectious throughout this time, it is clear that the antibody test is not suitable for the early diagnosis of the disease and the need for quarantine. However, both the WHO and the ECDC have recognized that antibody testing may be required for subsequent epidemiological studies. The sample used for antibody analysis is blood.

Currently, the quick tests provided are mostly based on antibody detection. In addition to the fact that such tests are not suitable for the early detection of disease, there is no overview of the quality of the tests provided, including their sensitivity and specificity.

In conclusion, based on up to date knowledge and technology, the only reliable method for the early diagnosis and detection of infectious cases of COVID-19 in a laboratory-based SARS-CoV-2 RNA test, which is mostly done from nasopharynx swab material.

Much has also been said about the lack of diagnostic tools in the world, which is true because of the worldwide spread of the virus and the consequent need for multiple diagnostics. However, the capabilities of diagnostics and related equipment manufacturers are adapting to the ever-increasing demand, and the need is increasingly being produced and supplied. In Estonia, the situation is currently under control with the detection of relevant viral RNA, and laboratories are able to carry out sufficient analyses. Rainar Aamisepp, head of SYNLAB, the largest laboratory for SARS-CoV-2 virus RNA analysis, comments: „SYNLAB Estonia’s Tallinn laboratory has sufficient amount of diagnostic tools and equipment necessary for reliable COVID-19 testing, we have launched parallel technological processes in the laboratory, multiplied the number of specialists in the respective laboratory department, organized 24/7 work. In addition, we, in cooperation with our partners, have provided sufficient capacity for sample collection and logistics to cover the needs of COVID-19 laboratory diagnostics across Estonia. Many hospital laboratories have appropriate on-site RNA detection capabilities for quick diagnostics. ”

Clinical microbiologist Dr Paul Naaber adds: “As Estonia has sufficient capacity to provide adequate viral RNA detection methods for the diagnosis and detection of COVID-19 disease, there is currently no need to implement (quick) tests not recommended by various international specialized organizations. In my opinion, this would make the COVID-19 diagnostic more confusing. “