Covid-19: What tests are available?

	Covid-19
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Covid-19: What tests are available?
(as of May 2020)
The first and still most common way to test was invented in Germany and uses polymerase chain reaction (PCR). The virus multiplies rapidly in your body and it seems that, whether you get sick or not, you expel that virus when you breath and even when you speak. So the nurse simply picks up a nasal swab and the machine checks if there is a sign of the virus (if there is DNA or RNA associated with that virus). If and when the immune system destroys the virus, it means that your immune system has produced the appropriate antibodies. This usually takes a few days. You can be tested (easily) for these antibodies circulating in your blood. If you have them, in theory you are immune to re-infection, and therefore you should not be a threat to others. I write "in theory" because nobody really knows for how long the immunity lasts. Germany and Britain were the first countries to consider testing people for antibodies so that the ones who are immune can go back to normal life. The problem is that antibody tests are notoriously inaccurate. PCR testing is pretty accurate: if viral DNA or RNA is detected in your nose, there aren't many doubts about it. But you may have antibodies against some other coronavirus (like the common flu) that may fool the antibody test.
More details below.
In mid-January Christian Dorsten in Germany published a paper that describes how to make a test kit for covid-19, and by January 28 China had approved five test kits for covid-19. I think there is consensus that the USA wasted precious time when the test kit didn't work. The first antibody ("serological") test for covid-19 was unveiled by Linfa Wang's team at Duke-NUS in Singapore at the end of February. But the first serology test approved in the USA by the FDA was the one made by Cellex and that happened at the beginning of April.
The test kits that everyone talks about look for the genetic material (the RNA) of the virus, typical in the saliva or in the nose and then amplify it using the Polymerase chain reaction (PCR) so it can be detected. There are two main types of test. The one used by everybody so far is a "molecular test" that uses PCR (more precisely, reverse transcription or RT-PCR), which detects whether or not viral RNA is present in samples from a patient. The first quantitative RT-PCR tests for detecting the covid-19 virus were designed and distributed in January by the World Health Organization. It takes several hours to do a RT-PCR, it requires highly trained personnel and expensive special equipment. And therefore this type of test is mainly done by large, centralized laboratories, which means that it also takes time to ship the samples to those labs. (A new method to detect viral RNA is loop-mediated isothermal amplification or LAMP, but most labs don't trust it). The second type is antibody test, in particular lateral flow assays, that detect the two protective antibodies (IgG and IgM) produced by covid-19 patients. It can give a result in as little as 15 minutes. (A new method to detect these antibodies is "enzyme-linked immunosorbent assay" or ELISA). PCR tests are highly accurate, lateral flow assays are less accurate. By March 23 Nature journal listed a dozen lateral-flow assays from North Carolina-based Cellex, Biolidics (Singapore), Biomedomics (China), Jiangsu Medomics (China), Guangzhou Wondfo Biotech (China), Innovita (based in Utah but the test is made in China), Predictive (also based in Utah but the test is also made in China), Xiamen AmonMed (China) , Segentech (South Korea), Pharmact (Germany), etc.
Lateral flow assays can test a variety of samples like urine, blood, saliva, sweat, and serum. They are a well-tested method for rapid at-home tests. The most common lateral flow test is the home pregnancy test. The serological test looks for antibodies to the coronavirus in the blood plasma, and one was developed at Stanford by Scott Boyd. They all detect IgM antibodies, which are made early and whose levels usually quickly wane, and IgG antibodies, whose levels rise more slowly after infection but usually persist longer. Commercial serological tests are now being developed around the world, but their quality varies.
On April 13 the FDA authorized the first at-home covid-19 saliva test, made by a lab at Rutgers University. Saliva tests detect the presence of the virus' RNA.
In January 2021 three at-home covid-19 tests were entering the market: BinaxNow (only available by prescription), Lucira (only available by prescription) and Ellume (over the counter, no prescription required).
In July 2020 the Daily Telegraph reported that the British government was making plans to distribute for free millions of units of a quick antibody test called "AbC-19 lateral flow test" (98.6% accurate) developed by Britain's Rapid Test Consortium (UK-RTC), a partnership between Oxford University and diagnostics firms, which could identify covid antibodies within 20 minutes.
An antigen test is similar to the antibody test because it uses immunoassays, but the assays used are for detecting proteins left behind by the virus. These are generally faster and cheaper. The FDA approved antigen tests from Quidel (in May), BD Veritor (in July) and LuminaDX (in August), but these need proprietary machines to read the results. In August 2020 Abbott introduced a cheap antigen test that doesn't require a special machine and can give results in 15 minutes; but it requires a health professional to administer it. Antigen tests are generally cheap and easy to use, but they are not as sensitive as PCR tests: they need a lot of viral material to generate a positive result. But this actually makes them better at detecting infected people at the time when they are more likely to infect others. Unfortunately, an over-the-counter antigen test is unlikely to be approved in the USA precisely because it is unreliable, even though it is reliable to find highly contagious people. Britain now has two rapid tests: Oxford Nanopore's LamPORE, that can test both saliva and swab for viral RNA and that yield results in under two hours, and DnaNudge's test kit that delivers results in under 90 minutes and can be done outside a laboratory; but both require proprietary machines.
A study by Becton Dickinson published in October 2020 showed that a quick antigen-based test may be better at identifying covid than the slow and expensive PCR test (paper) and a few days later similar results were announced by UC San Francisco using Abbott's BinaxNOW rapid antigen test, still the only one authorized by the FDA.
In November 2020, Adaptive Technologies reported that its T-cell test T-Detect Covid is more effective than the antibody tests (paper).
Now we also have tests based on CRISPR. In March scientists from the University of Buenos Aires in Argentina and their spin-off CASPR Biotech in San Francisco announced a test based on CRISPR. Then both Mammoth Biosciences (in collaboration with Charles Chiu`s team at UC San Francisco) and Sherlock Biosciences (in collaboration with Silicon Valley startup Cepheid), startups cofounded by CRISPR pioneers Jennifer Doudna and Feng Zhang, respectively, are promising rapid tests.

See also:
Back to FAQ/ Q&A about Covid-19,
Data on Covid-19 and selected sources,
Covid-19: How it may change the World,
The Clown & the Virus,
The Clown & the Virus - Part 2,
Trump's Virus,
Sinophobia & Covid-19,
Sinophobia & Covid-19 in US Media,
Was covid-19 made in the USA? in China? TM, ®, Copyright © 2020 Piero Scaruffi All rights reserved.
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