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COVID-19 Tests

The progression of the COVID-19 pandemic has created a need for efficient and reliable tests that allow for accurate diagnosis as well as epidemiological surveillance around the world. This article will present the currently available tests for COVID-19 identification and their comparative benefits.

There are two main types of tests currently in use for COVID-19: those that identify the virus itself through its molecular components (molecular assays), and those that search for traces of the presence of the virus through remaining antibodies in the human body, that remain as the memory of a past infection (serology immunoassays).

Molecular Assays

These tests are genetic assays based on a molecular analysis technique called RT-qPCR, or reverse transcriptase polymerase chain reaction. They are the recommended method for identifying COVID-19 cases and are validated by the World Health Organization (WHO). This technique allows for the identification of the genetic material of the SARS-CoV-2 virus, which causes COVID-19 disease. They are used for diagnosing the active disease. The genetic material of the virus can be extracted from several sample sources, also called specimens, such as:


 * swabs from the pharynx or nasopharynx
 * sputum
 * tracheal aspirate
 * bronchoalveolar lavage
 * blood
 * urine
 * stool

The PCR tecnhique amplifies the genetic material, which then goes through fluorescence reactions to identify the virus.

Serology Immunoassays (SIAs)

These tests detect antibodies or antigens related to the body's immune response to the SARS-CoV-2 virus, which identifies people who have already fought the virus and developed immunity. Since they can keep track of people who are already recovered from COVID-19, they are used for epidemiological tracing. They are faster and less costly than genetic tests.

SIAs detect immune memory proteins called immunoglobulins, particularly IgG (associated with virus exposure some time ago) and IgM (related to recent exposure to the virus) in the case of SARS-CoV-2.Blood samples are analyzed using several technologies, such as Lateral Flow immunoassay (LFIA) and Enzyme-Linked Immunosorbent Assay (ELISA), which act by binding the antibody to an antigen and then creating a complex that is detected by the an immunochromatographic test. This provides several advantages, because the reaction time is short (5-20 min) and there's no need for specialized equipment. Still, there's the risk of false negatives if the virus is not very active, but on the positive side it can detect people without or with very few symptoms at the time of infection. Immunoenzymatic and immunofluorimetric assays are also used to monitor the epidemiological situation.

Factors impacting results


 * 1) Sensitivity: capacity to identify all infected people.
 * 2) Specificity: the ability of a test to detect a particular virus.
 * 3) Reagent stability: reagents that can be kept at room temperature allow for wider use.
 * 4) Turnaround time: the time it takes from taking a sample to delivering a result, which can go from minutes to days.
 * 5) Cost and platform accessibility: some tests require expensive laboratory equipment, that only large facilities have.
 * 6) Technical ability required: reading the results of a test can be as simple as detecting a color change with the naked eye to being able to operate analytical machinery.
 * 7) Minimum sample: the amount of virus protein, antigen or antibodies that are required for detection.

Result types

False negatives occur when an infected person has a negative result. This can happen because of a laboratory error, the stage of infection, or the type of sample collected.

False positives occur when a non-infected person has a positive result. This happens sometimes because of cross-contamination of samples, or because a sample was not correctly identified.

Glossary