Everything You Need to Know About COVID-19 Testing

This holiday season, many Filipinos relaxed into their usual holiday traditions, confident in their status as fully vaccinated. Then came Omicron. The new variant is infecting both vaccinated and unvaccinated people alike. Countries around the world are seeing record rates of infection.

With vaccines proving to be less effective than hoped, testing still plays a critical role in containing the pandemic. Yet, two years into the COVID crisis, many people remain confused about their testing options. What are the differences between COVID tests and which one is best for you? What’s the right time to test for COVID? Let’s drill down into each test’s strengths, limitations, and procedure.

Different types of Tests:  Rapid Antigen vs. PCR

Two major types of tests are used to diagnose COVID-19: PCR tests and Rapid Antigen tests. Each test detects a different part of the virus, which affects the accuracy and processing time. It’s important to understand the pros and cons of each test, and when to use them.

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PCR Tests

Quick take: A PCR test can detect infection sooner, but results take longer.

A PCR test looks for the genetic material of the virus. It can identify even tiny amounts of coronavirus DNA, making it a highly sensitive test. But processing results take 1-3 days–and even longer during a COVID surge. The waiting time means the PCR test, despite being the gold standard, isn’t ideal for every situation. For example, high-risk patients need fast diagnosis and intervention, before their symptoms become severe.

When should you use a PCR test?

PCR tests are commonly used to:

• Detect COVID in patients who are asymptomatic or have a low viral load.
• Confirm Rapid Antigen test results.
• Test patients before hospital admission.
• Make clinical decisions about treatment.

How accurate are PCR tests?

PCR tests are very accurate when performed by a trained health worker.

Rapid Antigen Tests

Quick take: Rapid Antigen tests are cheaper and can be processed in just minutes, however it may miss some cases.

The Rapid Antigen test looks for viral proteins, called antigens. It’s faster and cheaper than a PCR test. The drawback is it’s less accurate. You need a sufficient amount of virus particles in your system to trigger a positive result. That means the test is very good at detecting coronavirus if you have a high viral load. Rapid Antigen tests can, however, miss the earliest stages of COVID infection.

When should you use a Rapid Antigen test?

Rapid Antigen tests are the most common diagnostic test for COVID-19. In many instances, they’re preferred over a PCR test, such as:

• Group settings. Rapid screening tests can identify sick people before they expose others at school, work, events, or during travel.
• Patients who are at risk for severe illness. Quick diagnosis and treatment is needed for patients who may need clinical intervention, such as the elderly and people with comorbidities. It’s better to get the rapid test first, then confirm with a PCR.
• Cheap and accessible. PCR tests are cost-prohibitive for many people so an antigen test could be a more affordable solution.
• Recovered patients. If you have tested positive for COVID in the last 90 days, the CDC does not recommend a PCR test. Due to its high sensitivity, a PCR test may give a false-positive long after you’ve recovered.
• Symptomatic patients. Rapid testing allows for faster identification, tracing, isolation, and treatment of sick patients.

How accurate are Rapid Antigen tests?

Accuracy ranges between moderate to high during peak viral load.

COVID Test Procedure: Nasal, Saliva, Throat

Both PCR and Rapid Antigen tests require a sample collected from the nose, throat, or saliva. Accurate results depend on the quality of your specimen, so it’s important to follow the manufacturer's instructions to the letter. Below you can find a description of how each type of sample is collected, and who it’s best for.

Shallow Nasal Swab (Anterior Nasal Specimen)

• Can be performed by anyone.
• Also known as the “painless” nasal swab.
• Insert the swab ½ to ¾ of an inch inside the nostril.
• Firmly rotate the swab against the nasal wall at least four times. Repeat in the other nostril using the same swab.

Who’s it best for?

The shallow nasal swab test is less invasive and pain-free. It’s better for children, people with a deviated septum, or anyone that wants a more comfortable test.

Is it available in the Philippines?

Yes. The Abbott Panbio test is FDA and RITM approved. It comes with a comfortable, minimally invasive nasal swab. A nurse is not required for collection. Other available painless nasal swab tests include the Genbody COVID-19 Ag and the Sofia 2 SARS Antigen FIA.

Is it accurate?

The accuracy of a nasal swab test varies between manufacturers and depends on correct specimen collection. The sensitivity and specificity of common nasal swab tests in the Philippines is listed below:

Abbott Panbio (symptomatic patients): Sensitivity 98.1%; Specificity of 99.8%

Genbody COVID-19 Ag (symptomatic patients): Sensitivity 92.31%; Specificity 99.04%

Sofia 2 SARS Antigen FIA (symptomatic patients): Sensitivity 96.7%; Specificity 100.0%

Deep Nasal Swab (Nasopharyngeal Specimen)

• Must be administered by a trained healthcare worker.
• The patient's head is tilted back to a 70 degree angle.
• A trained healthcare worker inserts a flexible, 6-inch swab into your nostril.
• The swab is gently guided to the nasopharynx. This is the area where the nasal cavity meets the throat.
• The swab is then swirled or rolled for a few seconds to collect the specimen. You may experience discomfort, sneezing, gagging, and teary eyes. This is a normal reflex.
• If the first sample is insufficient, the process may be repeated in your other nostril.

Who’s it best for?

Most adults feel only minor discomfort during the deep nasal swab testing. However, people with a low tolerance for discomfort may prefer a less invasive option.

Is it available in the Philippines?

Yes. Many nasopharyngeal tests are approved for use in the Philippines, including the Roche Rapid Antigen Test, STANDARD™ Q COVID-19 Ag TEST KIT, and the NowCheck COVID-19 Antigen Test. Unlike the painless nasal swab, a medical professional is required for the insertion of the longer nasopharyngeal swab.

Is it accurate?

Nasopharyngeal tests are highly accurate when administered by a trained medical professional. Time between exposure and testing is also a factor. The accuracy of some common test brands in the Philippines is evaluated below.

Roche Rapid Antigen Test (symptomatic and asymptomatic): Sensitivity 96.52%; Specificity 99.68%

STANDARD™ Q COVID-19 Ag TEST KIT: Sensitivity 66.7% to 100%

NowCheck COVID-19 Antigen Test: Sensitivity 89.2%; Specificity 97.3%

Saliva Specimen

• Can be collected by anyone.
• Collect 1-5 mL of saliva in the sterile, leak-proof container.
• May take several minutes to collect an adequate sample.
• Most manufacturers recommend not eating or drinking before the test.

Who’s it best for?

The saliva test is another non-invasive test that can be collected by the patient. It may not be suitable for patients with dry mouth.

Is it available in the Philippines?

The only authorized lab for the PCR Saliva test is the Philippines Red Cross. You can find other saliva tests on the Philippine market, but they may be unreliable or counterfeit.

It is accurate?

Saliva PCR tests are very accurate, as long as you use a valid (not counterfeit) test. Research published in the journal of Clinical Microbiology and Infection indicated a specificity of 84.2% and sensitivity of 98.9%.

Throat Swab (oropharyngeal specimen).

• Must be collected by a trained healthcare worker.
• Insert swab into the posterior pharynx.
• Swab both tonsils and the posterior pharynx, taking care not to touch the patient’s tongue, teeth, or gums.

Who’s it best for?

Experts have theorized that the throat swab may be better at detecting the Omicron strain. However, more research is needed to make the call. For now, the test is best for people who cannot tolerate nasal swabs.

Is it available in the Philippines?

Yes. Throat swab tests approved for use in the Philippines include the SARS-CoV-2 Fluorescent PCR Kit and Xpert Xpress SARS-CoV-2.

Is it accurate?

Oropharyngeal tests are highly accurate when administered by a trained medical professional. The accuracy of some common test brands in the Philippines is evaluated below.

SARS-CoV-2 Fluorescent PCR Kit: Sensitivity 88.1%; Specificity 99.6%

Xpert Xpress SARS-CoV-2: Sensitivity 97.8%; Specificity 95.6%

Other Types of Testing:  Pooled PCR Tests

Pooled testing combines samples from a group of people and tests them in one batch. Individual specimens are collected and then mixed in equal parts to create a test pool. If a batch tests negative, each patient is marked negative for COVID-19. If a batch tests positive, each specimen needs to be retested individually. Pooled testing can significantly reduce the time and cost of COVID testing.

Who’s it best for?

Pooled PCR tests are best for screening groups, such as employees, students, and event attendees. It is less useful in areas where there is an outbreak. Once COVID-19 prevalence reaches 10%, the pooled test is no longer useful due to the number of follow-up tests required.

Is it available in the Philippines?

Yes. Pooled PCR testing is provided by Singapore Diagnostics.

Does it matter what brand of COVID test I get?

Some countries, like the Philippines, lack the regulatory oversight to properly validate each COVID test. Counterfeiting is also a problem; up to 30% of medicines, vaccines, and medical supplies are counterfeit in the Philippines. To ensure you receive an accurate test result, pay careful attention to test branding. Before purchasing a test, you can reference the list of tests approved for use by the US Food and Drug Administration. It’s equally important to choose a trusted vendor who can verify their chain of procurement.

Is it possible to test too early?

Yes. If you test too early you may end up with a false-negative. Coronavirus can take a few days to replicate and show up on a test. If you’ve had an exposure or been in a high-risk area, wait 2-3 days to get tested–unless you're experiencing symptoms. Symptomatic people should get tested immediately to avoid exposing others.

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Should you retest if your first test is negative?

In certain situations it is best to test a second time. If you know you’ve been exposed, you should take a second test 2-3 days later to confirm results. Also, if your antigen test is negative but you’re experiencing symptoms, follow up with the more specific PCR test.

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