COVID-19 tests: Everything you need to know - Synlab

COVID-19 tests: Everything you need to know

Published by Synlab on 08 May 2024
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Understand how the new Coronavirus originated, how to diagnose, and what are the tests available and recommended, both for individuals who want to know whether they are infected or had contact with the SARS-COV2, the virus that causes COVID-19, and produced the necessary immunity antibodies. 


How did the COVID-19 originate? 

In December 2019, in Wuhan, province of Hubei, China, some cases of severe pneumonia with unknown cause were reported and epidemiologically related to a seafood market in Wujan. 

Then, in January 2020, a new coronavirus was identified, isolated in the lower respiratory tract of four suspected cases of severe pneumonia. This new coronavirus belonged to the family of viruses that cause severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS), as well as the four human coronaviruses associated to common cold. 

The new coronavirus SARS-COV-2, named initially 2019-nCOV by the World Health Organization (WHO) and later as SARS-COV-2 (Severe Acute Respiratory Syndrome Coronavirus 2), is a virus that belongs to the family coronaviridae from the genus betacoronavirus. This virus causes the disease that became known as Corona Virus Disease (COVID-19). 

On January 30, 2020, the World Health Organization declared that the outbreak of SARS-CoV-2 was a Public Health Emergency of international concern, and more than 80,000 confirmed cases were reported around the world by February 28, 2020. 

Currently, 55 million people were infected worldwide and more than one million lives were lost to the diseases.   


How to diagnose COVID-19? 

The diagnostic medicine has a fundamental role in the global fight against the coronavirus. As a response to the COVID-19 pandemic, SYNLAB Solutions in Diagnostics, present in 40 countries and four continents, has different laboratory tools developed for different goals. 

These laboratory tools, when adopted individually or as a set, allow developing protocols to obtain epidemiological data, occupational medicine, hospital discharge, return to the work environment or to life in society, among others.  

The tests available for detecting COVID-19 can be divided into two classes: 


1) Diagnoses for the new Coronavirus:  

The diagnostic tests are used to verify whether the patient is infected. The test consists of detecting genetic material (RNA) from the SARS-COV-2 virus in nasopharyngeal samples and respiratory secretions. Is generally known as molecular testing or nucleic acid amplification techniques (NAAT). RT-PCR is the gold standard, but not the only molecular test. 

RT-PCR Coronavirus test: can detect infection from the first day of symptom, in average, until the 21st day of infection 

  • Considered the gold standard for COVID-19 diagnosis.  
  • Molecular analysis, highly sensitive, enabling to identify contaminated patients soon after the symptoms appear up to approximately the 21st day since the infection. After this period, the amount of viral material (load) tends to decrease, making it more difficult to detect by this technique.  
  • Technique of choice in cases of monitoring infected patients, being mandatory for hospital discharge. 

To whom the Coronavirus RT-PCR Test is indicated: 

Since the RT-PCR test is a diagnostic test, which has the goal of assessing whether the patient is infected by the virus that causes COVID-19, is indicated for patients presenting symptoms or who have presented prior POSITIVE result, in order to find out whether they are still sick and infectious. Also indicated in contacts close to confirmed COVID-19 cases. 


2) Assessment of immune response: 

The tests for assessing the immune response are used to check whether the patient had prior contact and produced antibodies of immunity against the virus. The test consists of detecting antibodies that appear in the acute phase of infection (IgM/IgA) and/or antibodies that appear in the later phase of infection (IgG) and suggest immunity against the SARS-COV-2 virus in blood samples. It is important to consider that the time for these antibodies to appear may vary from person to person and in certain clinical conditions (such as immunosuppressed patients who may take a little longer to produce, or still haven’t produced, these antibodies). 

Antibodies or Serology:  

The serology tests consist on quantifying the antibodies produced against the SARS-COV-2 virus, that is, it assesses the response from the immune system to contact with the virus. 

  •  Analysis of the immune response conducted in blood/serum samples; 
  • Production of antibodies in average after the 5th day of the disease 
  • Indicated for individuals after the 5th day from the onset of symptoms or exposure; 
  • Like every serology test, if the result is negative, the possibility of infection must not be excluded. Therefore, the result must be assessed by the requesting physician, who will check the need for repetition.  


What are the types of test for serology?  

Between 5 to 10 days after the contact or onset of symptoms: 

  • IgA/IgM: Antibodies of the IgA/IgM type indicate recent contact with the virus, or acute infection. Antibodies of the IgA/IgM appear in the beginning of infection and, after a while, start decreasing, until they are no longer detected.

Between 10 to 15 days after the contact or onset of symptoms: 

  • IgG: Antibodies of the IgG type indicate immunity, that is, the individual had contact with the virus and it was enough to create immunity antibodies (IgG). However, there still isn’t concrete information on whether IgG antibodies are permanent against SARS-COV-2, and whether it always generate immunity. 


Quick test: The quick test also conducts the analysis of antibodies against SARS-COV-2. However, this analysis presents lower sensitivity and provides a qualitative result, that is, POSITIVE or NEGATIVE. It must be performed by a trained health professional and with all biosafety measures. 


How is the COVID-19 quick test conducted? 

  • The test is conducted in a mobile device, through a capillary blood sample, in which the positive or negative result is visually interpreted by the appearance of bars for each antibody (IgM or IgG) 
  • . 

When must the COVID-19 quick test be conducted? 

  • When is it recommended? 

Since it needs a higher amount of antibodies, it is recommended that it is conducted as of the 10th day after the contact or onset or symptoms.  

  • When is it not recommended? 

Due to the long detection window period, its isolated use as a tool for acute/early detection is not recommended, because it may generate a high number of FALSE NEGATIVE results. 


To whom is the COVID-19 quick test recommended? 

The tests for analysis of antibodies are indicated for individuals who want to know whether they had contact with the virus and produced immunity antibodies, or for epidemiological control. 


What are the differences between the PCR and Serology tests for COVID-19? 

The difference between the COVID-19 tests consists on the purpose of the analysis, as well as the necessary sample, that is, to know whether the individual is or was infected. 

For the RT-PCR test, considered the gold standard: 

  • It identifies whether the individual is infected.  
  • The virus is detected by the viral genetic material. 
  • – The higher the viral load, the better the sensitivity. 
  • the samples selected is the nasopharyngeal swab, however, other types of samples from the oropharynx or respiratory tract can be used. 

For antibody or serology tests and quick test:  

  • It identifies whether the individual had contact with the virus. 
  • It identifies whether the individual produced immunity antibodies.  
  • The virus is detected by a serum or blood sample.  


Despite the fact that the quick test and the serology test check the presence of antibodies against SARS-COV-2, they also are different from each other: 

  • The serology test allows to quantify the results, presenting higher sensitivity. Performed on automated equipment. 
  • The quick test is a qualitative test that needs a higher amount of antibodies to be able to make the detection, thus it has lower sensitivity. It does not require laboratory equipment for its interpretation. 


About the SYNLAB Group

The SYNLAB Group is a leader in providing medical diagnostic services in Europe, providing a full range of clinical laboratory analysis services to patients, healthcare professionals, clinics and the pharmaceutical industry. Resulting from the merger between Labco and Synlab, the new SYNLAB Group is the undisputed European leader in medical laboratory services. 

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