Questions about PCR Tests vs Rapid Response Antibody Tests and Personal Protective Equipment
Q. What tests are available?
A. There are two main ways to test for infection with SARS-CoV2 (the coronavirus that causes COVID-19 disease). The first is a very sensitive test that looks for the RNA of the virus using a technique called RT-PCR. This can detect as little as one virus particle in swabs taken from inside the mouth or nose. These tests are now available from many US manufacturers and laboratories but are in short supply. This supply will increase rapidly over the next few weeks.
A second type of test measures the antibody responses to virus in blood serum. There are many virus components that our bodies make many different antibodies against. Some antibody is very useful, and kills the virus or stops infection, and some is less useful, binding to common parts of the virus but without helping our defenses. Rapid Response test kits that test for antibodies are the type of test kits described on this website.
The test itself is very simple: coat a test tube with a virus “mash” or ideally purified virus components, then add a tiny amount of a very diluted blood sample from the patient and let any antibodies bind to the test tube. Finally, develop the test to see if any antibodies are present.
At the start of the outbreak, most countries relied RT-PCR tests because these were fastest to develop. More antibody tests are now becoming available, which will increase reported cases as gaps are filled. Big differences in the groups being tested still make overall numbers between countries hard to compare. The WHO was very quick to develop an RT-PCR test and this remains the primary method, using a network of labs doing the same standardized test. This allows for consistent data but has stretched capacity from the vast scale of the outbreak and the speed of its development.
Q. How good are current COVID-19 tests?
RT-PCR is very specific and sensitive. However, once you have recovered the virus is eliminated and these tests can no longer tell if you’ve been infected. This creates significant uncertainty especially if someone has self-isolated due to mild and unclear symptoms. RT-PCR tests need a laboratory, so it takes time – even if the RT-PCR test itself only takes several hours, by the time you add sample collection, transport, and sample processing it can be days before the result is known. Rapid portable RT-PCR machines are the cutting edge of diagnostic technology, and COVID-19 tests are only just becoming available for these machines – but even the fastest machines take around two hours. These have been evaluated in the NHS to improve flu treatment.
As the coronavirus spreads more widely around the globe, scientists are starting to use a powerful new tool: a blood test that identifies people who have previously been exposed to the virus. This kind of test is still under development in the United States, but it has been rolled out for use in Singapore and China.
The current lab test used in the United States identifies people who are currently spreading the virus that causes COVID-19. That’s crucial information, but that test doesn’t reveal who had previously been infected. That’s important too for understanding the unfolding epidemic.
The other test, used widely in science and medicine, detects antibodies that people produce after they’ve become infected with a bacterium or virus. Those antibodies can appear in the blood one to three weeks after infection, and they’re part of the immune system’s response to infection.
The antibody-based tests can identify people who were not known to be infected “either because they never developed symptoms, or they had symptoms that were never correctly diagnosed,” says Lauren Ancel Meyers, a biology professor at the University of Texas at Austin.
Because the symptoms of covid-19 are similar to those of other diseases, testing is the only way to know for sure if someone is infected with the coronavirus. Mass testing is therefore crucial to halting its spread.
Q. How do you test for coronavirus infections?
A. At present, most tests are based on looking for genetic sequences specific to the covid-19 coronavirus. If these sequences are found in a sample, it must contain the virus.
Q. What does testing involve?
A. Getting a sample to test involves pushing a swab – which resembles an extra-long cotton bud – deep inside the nose or to the back of the throat. The swab is then sent off to a lab.
Q. What about testing blood or urine?
A. The virus is only detected in the blood, urine or feces of roughly half of those who test positive based on nose or throat swabs, so blood, urine and stool tests aren’t reliable. If you are coughing up sputum, testing that can provide more accurate results than a nose or throat swab, according to a handbook summarizing findings in China.
Q. How long does it take to get a result?
A. Most labs use a method called the polymerase chain reaction (PCR), which takes several hours. It can take days for labs to run the tests and tell people their result. Several groups around the world, are developing faster genetic tests, typically based on a method called loop mediated isothermal amplification (LAMP), which takes less than half an hour. Handheld LAMP tests that could be used in homes and airports may start
Q. How accurate are the tests?
A. In theory, genetic tests should be extremely accurate if done properly. However, there have been reports from China of many false negatives and false positives. This may be because the swabbing wasn’t done correctly, or because overworked lab technicians were making mistakes. In addition, if people are tested very soon after becoming infected, they may not be shedding the virus yet.
Q. Why is it so hard to get tested in most countries?
A. There are obvious practical issues with scaling up testing, from lack of trained personnel to equipment. But South Korea, which is now testing more than 20,000 people per day, has shown how fast it can be done. Many other countries didn’t start ramping up testing capacity until local case numbers began to soar and – unlike South Korea – haven’t made testing central to their strategy as advised by the World Health Organization.
Q. Some tests can be done in 10 or 15 minutes. How do they work?
A. Rapid tests, such as those shown on this website, are usually based on detecting proteins rather than genetic sequences. These proteins can either be viral ones, called antigens, or the antibodies our bodies make to kill the virus. Antigen tests can directly detect the presence of the virus, but are less accurate than genetic tests.
A. What about antibody tests?
A. The downside of antibody tests is that they cannot detect infections in the first two weeks or so, when people are most contagious. However, our bodies keep making antibodies even after we have recovered from an infection, so testing people’s blood for antibodies against the coronavirus will reveal how many of us have been infected so far. This will help us calculate the infection fatality rate.
Q. Can antibody tests distinguish between people who have recovered and those who are still infected?
A. Sometimes. People start producing so-called IgM antibodies against the coronavirus around 10 days after showing symptoms (perhaps 15 days after infection). After another two days, their bodies start making IgG antibodies, and gradually stop making IgM. Most people will recover fully as soon as IgG levels ramp up. Many rapid tests can detect both types of antibodies. If IgM antibodies are present in someone’s blood, they are likely to be still infected. If only IgG is present, they are recovering or fully recovered.
Q. How accurate are these rapid tests?
A. The results from the clinical trial data from China are considered very accurate. These tests are being validated in the USA at the moment for several different rapid test kits made by different manufacturers and should be completed by mid-April. Numerous companies are producing different tests that haven’t been independently checked yet. In general, testing for antigens or antibodies is less accurate than genetic testing, but the tests are easier and cheaper to manufacture and much cheaper to administer since they can be done by doctors, nurses and other health care professionals when used at the point-of-test. Rapid tests could play a valuable role, especially in poorer countries with little testing capacity. If they can reliably tell us when people have already been infected, it would allow key workers – especially in healthcare – to continue working without worrying about becoming infected or infecting their families.
Q. How do manufacturers ensure personal protective equipment (PPE) is safe and effective?
A. To help ensure medical devices, including PPE are safe and effective, the FDA has established Quality Systems Regulations and Good Manufacturing Practices. Manufacturers are expected to use these regulations and practices to maintain consistent product quality and to guide performance testing to make sure that their products conform to recognized consensus standards. For PPE, these standards may include for fluid resistance, leak protection, filtering capacity, or resistance to tears and snags. When these regulations and practices are followed, they provide reasonable assurance that the device is safe and effective.
FDA has also issued device-specific guidance for some products so that manufacturers understand the Agency’s expectations. Search for FDA Guidance Documents
Q. Will personal protective equipment protect against a specific disease?
A. PPE are designed to create a non-disease specific barrier to penetration of substances, solid, liquid, or airborne particles. In general, neither FDA nor the manufacturer can provide assurances that PPE will protect you against a specific disease. The data that FDA uses for the evaluation and clearance of PPE rarely includes performance evaluation or testing against specific viruses, such as Ebola or flu. If performance data has met FDA requirements and demonstrate protection against a specific disease, the product labeling will state the claim for protection against a specific virus or bacteria.
When there is an outbreak that affects the broad population, The Centers for Disease Control and Prevention (CDC), is responsible for making specific recommendations for infection control measures in different circumstances and settings. For example, the CDC has provided the following recommendations:
What You Should Know about the Flu
What You Should Know about Ebola✎ EditSign
Q. Should caregivers use PPE to help protect against infection when caring for a sick person at home?
A. In some circumstances, a health care provider may recommend that caregivers use PPE when caring for a sick person at home. It is important to know that the use of PPE alone will not fully protect you from acquiring an infection or passing an infection to another person. Other infection control practices, such as hand-washing, using alcohol-based hand sanitizers, isolation of patients and using properly covering cough and sneezes, are also important steps to minimize your risk of infection.
Additionally, please be aware of proper removal and disposal procedures. Even if PPE successfully protects you while it is worn, improper removal and disposal of contaminated PPEs can expose the wearer and other people to infection.
Q. Where can I buy PPE?
A. Most types of PPE are available without a prescription. Pharmacies, medical supply stores, and Internet medical supply retailers sell PPE.
For more information about buying medical products on the Internet, see FDA’s website on Protecting Yourself.
Q. Can I reuse PPE?
A. In general, most PPE is designed to be used only one time and by one person prior to disposal. There are a few exceptions, for example some types of elastomeric respirator masks and protective eyewear such as goggles may be reused if the user follows decontamination methods in the product labeling.
If PPE is exposed to infectious materials during use (e.g., body fluids from an infected person) the PPE is considered contaminated and the wearer should remove it promptly, using proper removal and disposal procedures. Please be aware that even if a PPE successfully protects you while it is being worn, improper removal and disposal of contaminated PPEs can expose the wearer and other people to infectious agents.
Q. Can I wash disposable PPE?
A. No. Disposable PPE is designed to be used only one time and by one person; it cannot be washed. Washing PPE changes its protective or barrier capabilities, and it may no longer be effective.
Q. Can I share PPE with other users?
A. In general, most PPE cleared by the FDA is intended to be used only one time and by one person. Sharing PPE is not advised. The protective capabilities of single use PPE cannot be assured when it is reused by the same person or used by more than one person. Sharing PPE that is intended for single use may expose another person to infectious materials. PPE should be removed promptly after use and disposed of properly.
Q: Does every piece of PPE provide the same level of protection?
A: PPE is designed to be used with other infection control practices such as hand-washing, using alcohol-based hand sanitizers and covering coughs and sneezes to minimize the spread of infection from one person to another.
Wearers of PPE can determine what protective level a PPE is rated for by the standards to which it has been tested.
CDC’s National Institute for Occupational Safety and Health (NIOSH) maintains a database called NIOSH Personal Protective Equipment Information (PPE-Info)that includes most of the current PPE standards in more detail.
Q: If I experience a problem with my PPE, what should I do?
A: If you suspect or experience a problem with your PPE, we encourage you to file a voluntary report through MedWatch, the FDA Safety Information and Adverse Event Reporting program and notify the manufacturer.
Health care personnel employed by facilities that are subject to FDA’s user facility reporting requirements should follow the reporting procedures established by their facilities.