3 Methods to diagnose COVID-19

The outbreak of the novel COVID-19 is an epidemiological threat to the nations. The techniques are available to diagnose COVID-19 alerts the countries to curb the spread quickly. Many fake news or misconceptions about the techniques and testing kits could mislead the information and health concerns extending to economic crises.

3 methods to diagnose COVID-19 or coronavirus infection.
  1. Nucleic acid amplification test (NAAT) – real-time reverse-transcriptase–polymerase-chain-reaction (RT-PCR)
  2. Serological (Antibodies) testing
  3. Chest radiograph or computed tomography (CT)

World Health Organization standardized the biochemical methods like RT-PCR and serological tests to diagnose COVID-19 as of February 2020. However, research studies confirmed that image analysis could be an advent methodology to assess the infected patient.

Amidst, RT-PCR stands out for the accurate detection of the novel coronavirus (SARS-nCoV-2). Many countries are preparing RT-PCR or mini-RT-PCR kits for fast accessing of the diagnosis results. Due to the high numbers of spreading, nations rely on other tests like antibodies or CT-Scan. However, it is mandatory to confirm through RT-PCR test to declare the patient is infected or not by SARS-nCoV-2.  

NAAT (RT-PCR)

It is the method based on the detection of unique sequences of COVID-19 virus RNA using a nucleic acid amplification test. Real-time reverse-transcription polymerase chain reaction (RT-PCR) is used to detect specific viral genes of COVID-19. It includes three stages, such as extraction, amplification, and analysis. Extraction of nucleic acids from the assay of nasal, pharyngeal swab specimens are employed to identify specific genes for the confirmation of infection.

Pneumonia based severe acute respiratory pandemic diseases (SARS-nCoV-2) have a 70% similarity of its genome with the previous version of SARS-coronavirus. From the knowledge index, RT-PCR assay was prepared to inspect and distinguish the novel coronavirus from other types of coronavirus such as alphacoronaviruses, betacoronaviruses, and middle east respiratory syndrome-related coronavirus. WHO conducted cross-verification tests with known respiratory viruses and bacteria in clinical samples before confirming the standardization of testing kits

Finally, WHO recommended three types of genes for the confirmation of SARS-nCoV-2 genomic RNA as a positive control. 

First-line screening assay: E gene assay
Confirmatory assay: RdRp gene assay
Additional confirmatory assay: N gene assay 

Most of the testing kits are based on the assay for one or any two genes. Compared to one, testing for two gene assays will result in most confirmative reliable data due to the practical difficulties like sampling, testing conditions, etc.

Relative positions of amplicon targets on SARS-CoV genome and wuhan-CoV genome
Image credit: WHO (RT-PCR assays, Berlin, Jan 13, 2020)

Serological (Antibodies) test 

It is an indirect method considered as a secondary test protocol. The measurement of specific antibodies related to an immune response of COVID-19 in the blood (serum) samples. Compared to the RT-PCR test, it is rapid to analyze. The testing of SARS-nCoV-19 antibodies IgG and IgM from whole blood, plasma, or serum are commercially available rapid diagnostic kits.

CT Scan

Chest radiograph or CT scanning is becoming an advised tool for the diagnosis of COVID-19. After the investigation of 1014 patients in Wuhan, China, from Jan 6 to Feb 6, 2020, the author(s) had concluded CT scan could be a methodology to assess the infected patients. Results published in the Radiology journal confirmed the consistency of chest CT scan analysis with the standard RT-PCR testing. The statistical results of CT scan analysis have higher sensitivity than RT-PCR test values.

“Chest CT may be considered as a primary tool for the current COVID-19 detection in epidemic areas.” – Tao Ai et al., Radiology, 2020; 200642 DOI: 10.1148/radiol.2020200642

Similarly, American Roentgen Ray Society acknowledged in a recent publication that, chest CT scan is reliable with a low rate of misdiagnosis (3.9%) that could help for the rapid diagnosis of COVID-19. But CT scan images of other respiratory syndrome diseases might overlap with COVID-19 symptoms. Hence, it is mandatory to get an opinion from 2-3 radiologists or doctors with a history of patients.  

“We found that chest CT had a low rate of missed diagnosis of COVID-19 (3.9%, 2/51) and may be useful as a standard method for the rapid diagnosis of COVID-19 to optimize the management of patients. However, CT is still limited to identifying specific viruses and distinguishing between viruses.” – Yan Li & Liming Xia, Tongji Hospital, Wuhan, China. American Journal of Roentgenology: 1-7. DOI: 10.2214/AJR.20.22954

COVID-19: Common features of CT scan

  • Ground-glass opacities (GGOs) and consolidation with or without vascular enlargement
  • Interlobular septal thickening
  • Air bronchogram sign

Outlook

In the end, the suspect or infected patients must be analyzed every day to confirm the presence of the COVID-19 virus. Several factors affect the symptoms of COVID-19. Even after recovering from the infection, there will be a possibility of virus proliferation. Hence, it is mandatory to test frequently.

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