All About Covid Tests

In the midst of the information overload on Covid-19 tests, Dr Alok Pal Singh explains what is what

The topic that has taken over our lives and one which everyone in the world is worried about is Covid-19 (referred to hereafter as Covid). This is also sometimes simply referred to as Coronavirus, which can be misleading since other types of human coronaviruses also exist and cause the common cold among other things. Covid is specifically caused by a new and novel strain of the virus that emerged from Wuhan, China in December 2019 called the SARS-Coronavirus-2 (SARS-CoV-2). As there is no proven specific treatment for this virus to date and vaccination is under development, our best strategy at present is to avoid contact with someone who is suspected or has confirmed Covid.

Possible symptoms

Suspicious symptoms of Covid include:

• Fever
• Cough
• Shortness of breath
• Tiredness
• Sore throat
• Headache
• Loss of taste or smell

Diagnosis of Covid should ideally be confirmed with a laboratory test since other viral infections like flu can also cause similar symptoms.

If you do have any one of these symptoms, you’re advised to see a doctor who may advise you to undergo a diagnostic test for Covid detection. If you have none of these symptoms but have recently have come in contact with a person who had Covid there may still be a chance that you have Covid, but are asymptomatic.

The diagnostic tests available in your local hospital or testing center may be for screening or confirmation of Covid.

The tests available for diagnosing Covid have differences in terms of targets in the virus or human body, reporting times and performance assessed by the sensitivity and specificity of the test. Sensitivity is the ability of a test to correctly identify patients with a disease, whereas specificity is the ability of a test to correctly identify people without the disease.

What tests are available?

A brief description of the currently available tests is provided below:

1. Reverse Transcription – Polymerase Chain Reaction (RT-PCR)

The RT–PCR is a nucleic acid-derived method used to detect the presence of specific genetic material in any pathogen, including a virus.

RT-PCR is also a gold standard test to detect active SARS-CoV-2 infection. Here, a swab is inserted deep in the nose or back of the throat, usually the former. It takes around 4- 8 hours in general to obtain test results. . The sensitivity of the test is around 60-80% whereas the specificity is 90-95%.

TrueNat/CBNAAT (Cartridge-based Nucleic Acid Amplification Test) is one type of rapid PCR testing.

TrueNat is a chip-based, portable RT-PCR machine, originally developed as a portable diagnostic tool for tuberculosis. TrueNat has been validated by the Indian Council of Medical Research (ICMR) for Covid tests. Here again the sample is taken from the nose or throat with a swab. TrueNat can return results faster than the standard RT-PCR tests; results may take less than 60 minutes. The sensitivity of the test is lower compared to the RT-PCR test at 50-80% while the specificity is still at 90-95%.

2. Rapid Antigen Test

This test is aimed at detecting the virus antigen; that means this test detects the current infection. It can be used at the point-of-care. Nasal samples are collected and the results are interpreted in less than 30 minutes. This has been approved by ICMR for use in containment zones and healthcare settings. Sensitivity is around 50-84% and it has a high specificity above 99%.

Rapid antigen test kit. Picture: Roche

Rapid antigen testing device. Picture: Abbott Laboratories

3. Serology (IgM and IgG Antibody test)

Unlike the previous tests this test isn’t used for diagnosis but is intended for use as an aid in identifying individuals with an adaptive immune response to SARS-CoV-2, indicating recent or prior infection. It should not be used to diagnose acute SARS-CoV-2 infection. Moreover, negative results do not preclude acute SARS-CoV-2 infection. Here we require a blood sample and the results will be available in less than 30 minutes. With a sensitivity of around 93% and specificity of around 98% it is the most accurate and yet not 100% reliable, so the ICMR has advised that if patients test positive they have to undergo a confirmatory RT-PCR test before beginning treatment.

Rapid IgG/IgM antibody test. Picture: thebiologynotes.com

Tests under Development

New tests and methods are still being developed to detect the coronavirus.

ELISA (Enzyme Linked Immunoassay) based serological test being developed by the Indian Institute of Technology, Delhi which will not only be a ‘probe-free method’ unlike the RT-PCR test but also cost a fraction of the price. Additionally, this test is meant to be for home use and it would not compromise on the accuracy compared to the current gold standard RT-PCR test.

N1-STOP-LAMP test, which is a rapid molecular test which compromises slightly on sensitivity for being easy to use and giving results within 20 minutes. However, this isn’t meant to replace the RT-PCR test.

A new Oxford machine learning-based Covid test can provide results in less than 5 minutes with a high degree of accuracy, without any sample preparation required and can be used for mass testing. It works by labeling any virus particles found in a sample collected by a patient using short fluorescent DNA strands that act as markers. The researchers anticipate to start product development by early next year, with the potential of having the test approved and ready for use around six months after that.

The saliva-based or spit test that has been said to not only be less intrusive and cheaper but also deliver faster and more accurate results. Trials for saliva-based tests are still undergoing and are yet to be approved in India for mass use.

Feluda Covid-19 testing kit is said to give a test result in 45 minutes. It has been developed by the New Delhi-based CSIR-Institute of Genomics and Integrative Biology (IGIB) and the Tata Group. It has 96% sensitivity and 98% specificity. The Feluda test kit is very similar to a pregnancy strip test, in that it changes colour on detecting a virus from a nasal swab.

COVIRAP is another test that is being developed by Indian Institute of Technology, Kharagpur. ICMR has already validated the efficacy of this test. It includes an automated pre-programmable temperature control unit, a special detection unit on genomic analysis, and a customised smartphone app to produce results. It can deliver results within an hour. It has shown 94 per cent sensitivity and 96 per cent specificity. The machine is portable and has a capacity to test between 3 and 10 samples in one go. It uses a paper strip to detect virus from the nasal swab samples.

Apart from new methods being released to the public there have also been improvements on already existing tests such as the RT-PCR test. Reliance Life Sciences has developed a new RT-PCR kit that promises results within 2 hours. It is named R-Green Kit and has shown a 98.7% sensitivity and 98.8% specificity.

As existing and new tests continue to be improved and developed, we can be assured that diagnosing COVID will get quicker and easier. Stay safe and stay strong.