Julio 10, 2020



PCR (Polymerase Chain Reaction) is a technique that directly diagnoses the presence of the SARS-CoV-2 virus in the body. The SARS-CoV-2 virus that causes COVID-19 is composed of nucleic acid (RNA) inside a lipid envelope. The COVID-19 RNA-PCR test detects the nucleic acid present in the virus. The COVID-19 RNA-PCR test is currently the “golden standard” for diagnosing COVID-19.

During the initial phase of COVID-19, that is the first 14 days of infection, the viral load is high. A positive result on the COVID-19 RNA-PCR test would indicate an acute ongoing COVID-19 infection.

The samples for the COVID-19 RNA-PCR test can be obtained from various bodily fluids. Depending on the sample, the sensitivity of the test can be variable. The most sensitive sample is obtained from the nasopharynx. The COVID-19 RNA-PCR test is therefore sometimes also called a “swab test”.

In nasopharynx and oropharynx, the virus can be detected normally until day 14 from the onset of symptoms. During a latter stage of infection, samples from the lower respiratory tract, such as sputum are indicated.

Why is this analysis important?

As WHO Director General Tedros Adhanom Ghebreyesus said, “test, test, test” is crucial in slowing the advance of the coronavirus pandemic. Since there are no specific and effective treatments against this highly contagious new virus, the most effective measure we currently have is prevention.

Knowing if one currently have or previously had a COVID-19 infection is not only of interest to the tested individual, but also important from a public health point of view. Testing helps epidemiologists and policy makers better understand the prevalence, spread and contagiousness of the disease and tailor policies accordingly.


What does a positive COVID-19 RNA-PCR test mean?

The COVID-19 RNA-PCR test has a very high specificity for COVID-19. A positive result typically means that one has an ongoing COVID-19 infection.

What does a negative COVID-19 RNA-PCR test mean?

The sensitivity of the COVID-19 RNA-PCR test is unfortunately not very high, which means that a negative COVID-19 RNA-PCR does not completely rule out the possibility of an ongoing infection. If typical symptoms persist, retesting should be considered.

Other Considerations

  • No test can be 100% accurate. False positives and false negative results are both possible. A false positive results means that the result turns out positive even though the person in reality does not have COVID-19 or antibodies against COVID-19. While a false negative result means that the person may have COVID-19 or antibodies against COVID-19, but the test results turned out negative. At Melio, we strive to offer you the best possible test on the market with the highest possible sensitivity and specificity to avoid problems with false positive and false negative results.

  • In order to interpret the results of the COVID-19 RNA-PCR test, it is important to take into account the symptoms, and it is sometimes necessary to supplement it with the determination of IgG and IgM antibodies.

  • A positive result on the COVID-19 RNA-PCR indicates the presence of the virus in the sample, but does not imply that the virus is necessarily replicative, i.e. alive.


What is COVID-19?

COVID-19, short for “coronavirus disease 2019”, is a respiratory infection caused by the virus SARS-CoV-2 (Severe acute respiratory syndrome coronavirus 2). SARS-CoV-2 belongs to the large family of coronaviruses, and was first discovered in Wuhan (China) in December 2019. The number of confirmed cases of COVID-19 has then been rising every day since.

COVID-19 presents with flu-like symptoms similar to SARS (Severe Acute Respiratory Syndrome) and MERS (Middle East Respiratory Syndrome Coronavirus), which are two other coronavirus-caused diseases that caused global outbreaks in 2003 and 2012 respectively. Although COVID-19 is much less fatal than SARS and MERS, it’s global spread is unprecedented.

The spectacular spread of COVID-19 around the world has led the World Health Organisation (WHO) to declare the COVID-19 outbreak as a global pandemic on March 11, 2020. As of June 7, 2020, there have been 6 799 713 confirmed cases and 397 388 COVID-19-related deaths reported globally (

Moreover, it is estimated that the “real” number of cases is significantly higher than those diagnosed. Calculations published by the Imperial College COVID-19 Response Team in April 2020 showed that infection rates vary between 0.5% of the population in Norway (with the lowest estimate) and 15% in the population in Spain (with the highest estimate).

The pandemic of a new virus that we still know little about poses a tremendous challenge to the global community. The UN Secretary General António Guterres calls the COVID-19 outbreak “the biggest challenge for the world since World War Two”.

Natural progression of COVID-19

COVID-19 is mainly transmitted through droplets generated by coughing and sneezing, but also when we talk. We can also catch COVID-19 by touching contaminated surfaces. Exactly how long the SARS-CoV-2 virus can survive outside the body is unknown, but other coronaviruses have been previously been shown to survive from a couple of hours to a week, depending on the material of the surface if not disinfected.

After infection, it can take from 2-14 days before symptoms appear. This is called the incubation period. The most common symptoms of COVID-19 are the following:

  • Cough

  • Fever

  • Difficulty breathing

  • Runny nose

  • Blocked nose

  • Sore throat

  • Headache

  • Nausea

  • Muscle and joint pain

It is also fairly common to lose one’s sense of smell and taste for a period of time. Diarrhea has also been reported as a symptom.

According to the WHO-China joint mission report in February 2020, 80% of laboratory confirmed COVID-19 patients have mild to moderate disease, that is to say a flu-like presentation and does not require hospitalized care, while 13.8% has severe disease, with difficulty breathing and 6.1% has critical disease with respiratory failure, septic shock and/or multiple organ dysfunction.

Some people infected with the SARS-CoV-2 virus do not experience any symptoms at all. However, the exact proportion of asymptomatic carriers in the population and their role in the transmission of the infection is still unclear. Asymptomatic carriers of COVID-19 can only be revealed through testing.

There is currently no treatment that is fully effective or specific for the novel coronavirus, and those currently being used are either experimental or only partially effective.


Report from the American Society for Microbiology COVID-19 International Summit, 23 March 2020: Value of diagnostic testing for SARS–CoV-2/COVID-19. Patel R, Babady E, Theel ES, Storch GA, Pinsky BA, St. George K, Smith TC, Bertuzzi S. 2020., mBio 11:e00722-20.

Detection of antibodies against SARS‐CoV‐2 in patients with COVID‐19. J Med Virol. 2020;1–4. DOI: 10.1002/jmv.25820

The epidemiology and pathogenesis of coronavirus disease (COVID-19) Outbreak., Hussin A. Rothan. Journal of Autoimmunity.

Estimating the number of infections and the impact of non-pharmaceutical interventions on COVID-19 in 11 European countries. Department of Infectious Disease Epidemiology, Imperial College London; Imperial College COVID-19 Response Team. 30 March 2020

Coronavirus disease 2019 (COVID-19): Epidemiology, virology, clinical features, diagnosis, and prevention., Kenneth McIntosh, MD. UpToDate Apr 30, 2020