About

• The Standard Q COVID-19 Ag detection kit is a rapid chromatographic immunoassay for qualitative detection of specific antigens to SARS-CoV-2.
• It has been developed by SD Biosensor, a South Korea based company, having its manufacturing unit in Manesar, Gurugram.
• The kit, validated by the ICMR and the All India Institute of Medical Sciences (AIIMS), was different from the Rapid Antibody Test kit. 
• Sample used is nasopharyngeal swabs in this test, while blood is collected in the antibody test.
• The kits will allow faster diagnosis.

Why in News?

The Indian Council of Medical Research (ICMR) has recommended the use of Standard Q COVID-19 Ag antigen detection test in containment zones and healthcare settings in combination with the RT-PCR test.

More in the news

• An advisory released by the ICMR stated that the test has high specificity (ability to detect true negatives) and relatively low sensitivity (ability to detect true positives).
• The Council recommends the use of this test in containment zones or hotspots to test symptomatic persons with influenza-like illness and asymptomatic direct and high-risk contacts with co-morbidities of a confirmed case.
• The test can be interpreted as positive or negative after 15 minutes of putting the sample into the well by appearance of test and control lines, which can be read with a naked eye, requiring no specialized equipment. 
• The maximum duration for interpreting a positive or negative test is 30 minutes

Related information

About Rapid antibody testing 

• It involves conducting blood tests on people displaying influenza-like illness symptoms in containment zones, large migration gatherings, or evacuee centres.
• A rapid antibody test is conducted to determine the presence of antibodies IgM and IgG, which can be detected from the seventh day of the onset of COVID-19 symptoms.
• This test can help understand an individual’s capacity to fight the infection after the virus has invaded the body.
• A rapid test kit can produce results in just 30 minutes. 
• The rapid antibody-based test will help detect the growth rate of cases, effectively aiding the country develop a better containment strategy.

Not for diagnosis

• WHO does not recommend the use of antibody-detecting rapid diagnostic tests for patient care but encourages the continuation of work to establish their usefulness in disease surveillance and epidemiologic research.
• The rapid antibody tests may not be as accurate as the RT-PCR.
• These tests are known to throw up more false negatives than false positives which is why the US Centre for Disease Control recommends a molecular test like RT-PCR if a rapid antibody test throws negative results.

Issues with currently available rapid testing kits

• Though it is quick and it can be done by anyone without much training the currently available POC rapid testing kits have been brought into the market without quality assurance by the regulatory authorities of the countries in which they were manufactured and they lack the validation process.
• Several of the testing kits have been fast-tracked due to increasing demand, hence lacking in quality, with variable sensitivity from 30% to 80%. 
• The main concerns raised by several European countries and India are that these kits are showing a higher percentage of false negative reports.

RT-PCR

• For individual diagnosis and treatment of Covid-19, the test used worldwide is RT-PCR (reverse-polymerase chain reaction).
• Earlier it was also used for Ebola and Zika diagnosis.

About real-time PCR

• A real-time polymerase chain reaction (real-time PCR), also known as quantitative polymerase chain reaction (qPCR), is a laboratory technique of molecular biology based on the polymerase chain reaction (PCR).
• It monitors the amplification of a targeted DNA molecule during the PCR (i.e., in real time), not at its end, as in conventional PCR.

How is it performed?

• In this, a nasopharyngeal (nasal) or oropharyngeal (mouth) swab is taken and sent in a cold storage box to the central laboratory, where the viral RNA is converted to complementary DNA (cDNA) using reverse transcriptase, and amplified following the addition of a primer and fluorescent dye and DNA building enzymes.
• A positive test will be indicated by the raise in fluorescence.
• Depending on the equipment and method used, the time taken may vary between a few hours to a day to get the reports.

(Apart from nasal or oral swab, another option for RT-PCR is the bronchoalveolar lavage (BAL) method, which a bronchoscope is passed to obtain fluid from lungs or sputum. Sputum or BAL has a higher viral load, so there is a higher chance of virus detection than nasal or oral swab.)

Positives and negatives

• This test is very sensitive and specific and can detect even if a single viral RNA particle is present in the swab.
• False negative (negative test when the patient is actually COVID-19 positive) may be obtained in some cases due to improper swab sampling, prolonged time to get samples to the lab causing degradation of RNA.
• RT-PCR is expensive, while free in government labs. Until May end, the ICMR had capped the cost of a test at Rs 4,500 for private laboratories, but has since removed the cap for private labs, allowing states to fix their own prices.

https://www.thehindu.com/news/national/icmr-recommends-use-of-faster-covid-19-testing-kit/article31834925.ece