Dr. Sanjay Gupta: It can still be hard to get a coronavirus test — and that’s not the only problem

There are two different types of coronavirus tests that you have probably heard of. One is a molecular diagnostic test that can test for the virus itself, often called a rt-PCR test. The second is a serological test – a blood test – that detects antibodies, which are part of the body's response to the virus.

However, in the midst of our need to have more tests, some basic problems with these diagnostic tests can be overlooked.

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One is the speed of testing, which can take up to several days to get results. This is a potentially catastrophic deficiency. If someone is harboring the virus and has to wait for several days for a result, the person may be in real contact with dozens of people, unless they proactively isolate themselves, which many may not do, especially if they feel fine or asymptomatic.

But I wanted to focus on another fantastic problem many Americans probably haven't even heard of, and that is the accuracy of the tests. Or rather, the lack of accuracy.

Mike Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told us that we have many tests on the market that we have no idea how well they work.


In part, the problem started when the US Food and Drug Administration authorized emergency use for 56 coronavirus tests – 46 of them for molecular diagnostic tests. Although there was an understandable rush to increase testing, it also meant that the FDA had not independently evaluated and validated them to see if they were really working properly.

And as we learn, none of them do.


"And that's the challenge when it comes to understanding. If you get a negative result, is it really negative?" Asked Osterholm.

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To understand the problem, it is important to understand a technical concept: sensitivity.

Sensitivity is the ability of a test to identify those currently infected with the virus. If a test has a high "false negative" rate, it means it has poor sensitivity. It is not "sensitive" enough to pick up all the patients infected with the virus.

To better understand why it would happen, it is helpful to understand how these tests work. The diagnostic rt-PCR test is the one that requires the swab, or in some cases saliva. (The antibody test will require blood, either from a blood stain or from a vein. It is a good way to separate them from each other). "Rt" means reverse transcriptase. Because the new coronavirus is only a small RNA strand, the first thing to do is to transcribe RNA back to DNA, which is done through an enzyme in the test package. After this, the polymerase chain reaction "amplifies" DNA so that it can be more easily detected.

This is the gold standard for testing, but like Osterholm and Mark Olshaker wrote in the New York Times, the way these tests are performed may be insufficient. For example, "The FDA recommends 40 amplification cycles, but even after these, too little of the virus's genetic material can be present to be detectable," they write.

There are also several other factors that affect the accuracy of the tests, including the time from disease onset, the concentration of the virus in the sample, the quality of the sample collected from a person and how it is treated, and the precise formulation of the reagents in the test sets.


Dr. Gary Procop, chief of virology at Cleveland Clinic, evaluated five of the tests used to diagnose the Covid-19 patient after he and his staff noticed that they received varying results, depending on the tests they used. He led a team that evaluated over 200 tests using the five tests. And what did they find? Test sensitivities ranged from 85% to 100%

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Procop told CNN that the US Centers for Disease Control and Prevention test was 100% accurate. He also pointed out tests from Cepheid and Roche both tested with sensitivity above 95%.

However, the highly touted Abbott ID Now – a fast diagnostic that is actually a laboratory in a box – scored much lower. Although it can produce results in minutes, it only scores with a sensitivity of 85%. That is a false negative rate of 15%. Another analysis found that it potentially had a false negative rate of 25% – meaning it could miss up to 1 in 4 positive cases.

Thursday Dr. Francis Collins, director of the National Institutes of Health, testified before the Senate Health Education Labor and Pensions Committee about the implications of false negatives.

"If you are in a situation where you really do not want to miss a diagnosis of someone already carrying the virus, you would like something that has a higher sensitivity than that," Collins said.

In a hospital, a false negative rate of 15% to 25% can mean putting an infectious person into a regular hospital ward. It can also lead to an infected patient being sent back to a nursing home full of vulnerable people or even to the public in dozens of states that are premature. "These are the people we care about," Osterholm said, "stepping away from that testing procedure and thinking & # 39; I'm fine, I don't have to worry about transferring & # 39; when they actually do."

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When we asked the FDA to get out tests quickly affecting the quality of the tests, a spokesman for the agency said that the FDA's oversight does not end with an EUA and that it continues to track those tests and take action when needed.

Also remember that regardless of the sensitivity of the test, you can still test negative one day and test positive one day. The diagnostics are a snapshot and can only let you know that you are negative at that particular time.

The study of Procop and his team has not yet been peer reviewed, but they expect to publish the findings soon. He also noted that since he and his team were testing the diagnostics, Abbott issued a warning that the sensitivity of the test was affected by the chemical used to hold the virus sample – known as the viral transport medium.

In a statement, Abbott said, "This method can reduce the sensitivity of the test through dilution, which can potentially lead to false negative results."

The company added "ID NOW is designed for and commonly used in emergency rooms, physicians' office laboratories, emergency rooms and retail. This means that patient samples (swabs) are collected and tested directly on the ID NOW instrument, near the patient and without the use of VTM. (Viral Transport Medium). "

Abbott also pointed to a recent report from the Detroit Health Department, which found that Abbott ID Now results were consistent with the results of a traditional PCR test 98% of the time.

So where do we go from here?

"They have to undergo these tests carefully and basically take off the mark that doesn't work well," says Osterholm.

That's an idea that Procop also suggested. The FDA could "begin to review this data and ask manufacturers to do so, so that the performance characteristics are truly transparent to anyone who wants to use them."

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Right now, while manufacturers have to share sensitivity data with the FDA, however much they have to share with the public is unclear. These are companies that self-report accuracy – how do they determine them? How do they compare to each other? What is the standard? This is now important information for everyone. We shouldn't have to rely on regular teams, like Procops at the Cleveland Clinic, to study this. We need the FDA to intervene. Clinicians ask for it.

"It's now time to start a more traditional FDA process where we start looking at testing properties and defining them against what we would consider a gold standard," says Procop.

As Osterholm told me: "The bottom line is that this is a key requirement that the FDA must fulfill. They can't abdicate their responsibilities here. We need clear and convincing information on how well these tests work. And if they don't, then laboratories must be be aware of it and not use these tests. "

In our attendance for several tests, we must remember that a bad test is potentially worse than no test. And we need the data to know which tests are better than others.

The good tests must be supported, made widely available in local communities – pharmacies, kiosks, public places and maybe even in people's homes. They must be performed regularly, and of course they must be very accurate.

On Friday, the FDA granted the first authorization for emergency use an antigen diagnostic test for coronavirus. This test can quickly detect fragments of viral proteins by testing samples collected from a nasal swab. Unlike rt-PCR, which can take time and materials, antigen tests can reverse the results much faster. However, antigen tests are not as sensitive as rt-PCR diagnostics, and they can produce several false negatives.

And that brings us back to the original problem, the persistent lack of testing in the United States. So far, the United States has conducted over 8 million tests, according to the Covid Tracking Project. If a person took just one test – that would be about 2.5%. But one person can be tested several times, so we don't really know what percentage of the population has been tested.

Harvard's Safra Center for Ethics, along with a group of bipartisan public health and economics experts, released a roadmap that requires 20 million tests a day in mid-July to fully mobilize the economy. About 6% of America is tested every day.

Another way of thinking about it: It's like testing the entire country every 14 days.

The bottom line: We need a lot of testing. These tests must be performed regularly. The results must come back quickly. And the accuracy has to be amazing.

It is daring, but without a very effective medicine to treat Covid-19 or a vaccine to prevent the virus, this test quality is the most reliable way to restore a certain sense of normalcy. It will not only help contain the virus, but also give people the psychological confidence that they do not spread the virus unintentionally. This is how we achieve a reasonable security line to start reopening the country.

CNN's Nadia Kounang and Maggie Fox contributed to this report.

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