COVID-19 Diagnostic Methods And Tools: What You Should Know

As of April 24, 2020, the total number of confirmed COVID-19 cases in India is 23,077 including 4,749 recovered cases and 718 deaths. Seeing a 19-days incubation period of the virus, medical experts have suggested 14 days quarantine for people who are suspected or asymptomatic.

Early diagnosis of diseases plays a key role in controlling a pandemic. Researchers around the world are making continuous effort to develop a COVID-19 diagnostic method which is rapid and accurate to control the spread. Take a look at a few existing diagnostic methods for COVID-19.

1. Nucleic Acid Amplification Tests (NAAT)

It is regarded as a primary testing method for diagnosing COVID-19. NAAT is used to genetically detect and amplify a unique sequence of the COVID-19 RNA by reverse-transcription polymerase chain reaction (RT-PCR). [1]

The test is done mainly at the acute phase of the illness. RT-PCR test is highly sensitive and specific. It detects viral load even if it is low in number and prevents false-negative results. Also, the cost of testing is relatively optimal. The negative aspects of the PCR test are time and the requirement of additional parameters. [2]

2. Viral Sequencing

RT-PCR test is efficient in detecting COVID-19 virus sequence. However, it targets only the conserved region of the pathogen genome. As we know, pathogens keep mutating, therefore, the chances of false-negative results are more during the PCR test.

Viral sequencing is a next-generation sequencing (NGS) technique which includes metagenomics, amplicon-based NGS and hybrid capture-based NGS. It is highly sensitive than PCR method and can be used for secondary detection or double-checking the RT-PCR false-negative samples. The only negative side of this method is the high cost. [3]

3. Serological Tests

The test is used to detect the immune response by the body when it encounters a certain virus. Whenthe epidemic firststarted , the human body was unable to develop its antibodies as it was new to mankind. This has limited the diagnosis during the early days.

As of now, this treatment method is widely used by healthcare professionals to treat infected cases. They are doing it by a process called convalescent plasma in which the blood samples ofrecovered patientsare taken (with permission from the donor) and administered to patients who are critically ill or has lower chances of recovery. [4]

Serological testing is a kind of passive antibody treatment which is mainly used to help COVID-19 positive patients develop an immunity against the virus. This test is approved by the FDA. The negative aspect of the test is the presence of allergens or interfering substances in the blood of the donor. The process can be used when the NAAT test comes negative.

What Is Convalescent Plasma Therapy? Is It Effective To Fight COVID-19?

4. Rapid Antigen Tests

The test is known for fast detection and low cost. There are multiple types of rapid antigen test but among them, fluorescence immunochromatographic is accurate, rapid and simple. It helps detect the outer protein shell of the virus that contains genetic material in the nasopharyngeal swab and urine sample. [5]

Rapid antigen test has poor specificity in detecting coronavirus except for MERS. As most of the COVID-19 patients are not identified during the incubation period of the infection, this method does not serve as the best method for diagnosis of COVID-19.

5. Computer Tomography

It is a non-invasive method carried out by taking many cross-sectional images of a person's chest. The images are then analysed by radiologists to detect any abnormality in the lungs.

The severity of COVID-19 is found out based on the CT scan images. If it's just two days after the onset of symptoms, the CT findings will be normal while after 10 days, maximum lung involvement can be seen. Compared to RT-PCR, CT scan has a higher sensitivity of 86 to 98 per cent with less false-negative rates. [6]

Digital Stethoscope For COVID-19: What You Need To Know