Tag: false negative

What to Know About Home COVID Tests

They may be hard to get, but at least 16 different home COVID tests are now authorized.

Breaking News – you can now order 4 free at-home tests from the covidtests.gov site. (see below)

Home COVID tests that you can buy over-the-counter have been available for over two years now.

The first home COVID test was authorized by the FDA in December 2020.
The first home COVID test was authorized by the FDA in December 2020.

So why is it so hard to find one when you or your kids are sick and need to get tested?

At Home COVID Tests

Even though there are now many more types of home and OTC rapid COVID tests, it can still be hard to find these tests for one simple reason – high demand during COVID surges.

“The deliveries of tests from manufacturers to the U.S. government will begin over the next week or so. Americans will start receiving free tests in the coming weeks. We will set up a free and easy system, including a new website, to get these tests out to Americans.”

White House COVID-⁠19 Response Coordinator Jeff Zients

Being able to order free tests from the US Government will hopefully help satisfy that demand!

“Every home in the U.S. is eligible to order 4 free at-⁠home COVID-⁠19 tests. The tests are completely free. Orders will usually ship in 7-12 days.”

COVIDtests.gov

That ‘new website’ is now up and running at COVIDtests.gov.

At least 16 different home COVID tests are now authorized.
At least 16 different home COVID tests are now authorized.

Until you order and get your home COVID test from that new website, try and get your hands on whichever home COVID test you can, especially if you don’t have access to testing from your health care provider, a pharmacy, or clinic. After all, they have been all been authorized by the FDA to detect SARS-CoV-2, even if they are not formally FDA approved.

You should also know that:

  • home COVID tests are rapid antigen tests, so are not as accurate/sensitive as molecular or PCR tests
  • if your home COVID test is positive, then you have COVID and you should isolate yourself for at least 10 days (although there are some new options to end isolation early).
  • if your home COVID test is negative, understand that it doesn’t necessarily mean that you don’t have COVID… It really only means that the “the virus that causes COVID-19 was not found in your specimen.” While it may also mean that you don’t have COVID, it could also be a false negative. If you were recently exposed or your symptoms just started, stay in quarantine and test yourself again in a few days. Or consider getting a molecular or PCR test.
  • while most at-home tests are done using a nasal swab, some experts think that with the Omicron variant, doing both an oral swab of the throat and a nasal swab will give more accurate results. That is not how these tests were authorized by the FDA though. Home throat swabbing is also not easy to do by most people. To get the most accurate results, follow the manufacturer’s instructions and maybe don’t test on the first day or two of your symptoms. While you remain in isolation, wait for the viral load to increase in your nose and then test yourself. Of course, seek immediate medical attention if you develop severe symptoms at any point.

Home COVID Collection Kits

In addition to at-home tests, many types of home collection kits are available, in which you collect your sample at home, but then mail it to a lab for testing.

At least 16 different home COVID tests are now authorized.
At least 16 different home COVID tests are now authorized.

In fact, the FDA has authorized at least 63 home collection kits for COVID, including some that can be done on saliva samples!

Unfortunately, these home collection kits are also in short supply…

Fake COVID Testing Kits

Not surprisingly, fake at home tests are also a thing!

Make sure that you buy an FDA authorized at home test, which includes the:

  • BD Veritor At-Home COVID-19 Test by Becton, Dickinson and Company
  • BinaxNow COVID-19 Antigen Self Test by Abbott Diagnostics
  • BinaxNOW COVID-19 Ag Card Home Test by Abbott Diagnostics
  • BinaxNOW COVID-19 Ag Card 2 Home Test by Abbott Diagnostics
  • CareStart COVID-19 Antigen Home Test by Access Bio, Inc (marketed as on/go by Intrivo…)
  • Celltrion DiaTrust COVID-19 Ag Home Test by Celltrion USA, Inc.
  • CLINITEST Rapid COVID-19 Antigen Self-Test by Siemens Healthineers
  • COVID-19 At-Home Test by SD Biosensor, Inc
  • Ellume COVID-19 Home Test by Ellume Limited
  • Flowflex COVID-19 Antigen Home Test by ACON Laboratories, Inc
  • iHealth COVID-19 At-Home Test by iHealth Labs, Inc
  • InteliSwab COVID-19 Rapid Test by OraSure Technologies, Inc.
  • QuickVue At-Home OTC COVID-19 Test by Quidel Corporation
  • QuickVue At-Home COVID-19 Test by Quidel Corporation
  • SCoV-2 Ag Detect Rapid Self-Test by InBios International Inc.

Is your at-home COVID test not on the list?

Check the FDA for the latest list of authorized home COVID tests.

The FDA has sent warning letters to a number of folks marketing fake COVID tests.

And be on the watch for fake at-home tests.

What to Know About Home COVID Tests

For now, while we wait for more at-home tests, if you need to get tested, look for a COVID test wherever you can, whether it is with your healthcare provider, a local pharmacy or community clinic, an at-home test, or a test you collect at home and then send to a lab.

Your local or state health department might also be a good source for community testing and home collection kits.

And if you can’t find a test and think you might have COVID, just stay home in isolation and assume you have COVID.

What else can you do?

Get vaccinated and protected, including a booster dose of the COVID vaccine when it is available to you!

More on COVID Tests

Lab Tests That Are Often Misinterpreted

To get the most accurate results and avoid false positive and false negative results, you want to use the right test for the right patient, and then know how to interpret the results correctly.

There are a lot of good reasons that most doctors should do fewer lab tests.

For one thing, many are simply unnecessary.

And few tests are inexpensive.

Another reason, one that you likely haven’t thought of, is that sometimes lab tests are misinterpreted, leading to unnecessary treatments.

Lab Tests That Are Often Misinterpreted

In addition to false positive and false negative test results, which are an inherent risk with almost any test, you sometimes run the risk that your doctor doesn’t truly understand how to interpret the results of the test they ordered.

How is that possible?

Consider Lyme disease testing.

Unless you live in or visited an area with ticks that cause Lyme disease and you have symptoms of Lyme disease, then you don’t need to be tested for Lyme disease. If you do get tested, you doctor should use two-tiered testing – an EIA or IFA test first, and if positive, Western blot testing.

The CDC recommends two-tiered testing for Lyme disease.

How do you know if your Western Blot test is positive?

A positive IgM Western blot for Lyme disease requires at least two of the following bands of the test to be positive:

  1. 24 kDa (OspC)
  2. 39 kDa (BmpA)
  3. 41 kDa (Fla)

And a positive IgG Western blot for Lyme disease requires at least five of the following bands of the test to be positive:

  1. 18 kDa
  2. 21 kDa (OspC)
  3. 28 kDa
  4. 30 kDa
  5. 39 kDa (BmpA)
  6. 41 kDa (Fla)
  7. 45 kDa
  8. 58 kDa (not GroEL)
  9. 66 kDa
  10. 93 kDa (2)

What happens if someone only sees one of the IgM bands or four of the IgG bands? Are they going to know it is a negative test or are they going to wonder if they have Lyme disease?

Still, that doesn’t mean that you should never test patients for Lyme disease. You just want to use the right test for the right patient, and then know how to interpret the results correctly.

What other tests are often misused or can be easily misinterpreted?

  • blood allergy tests – Ever been told you’re child is allergic to everything? That’s likely because instead of a simple positive or negative result, blood allergy tests are prone to false positive results
  • the PPD test – it is important to understand that interpreting the tuberculin skin test depends on the child’s risk factors and that a previous BCG vaccine can trigger a false positive
  • rapid strep tests – prone to false positive results, picking up strep carriers, especially if you test kids who do not have classic symptoms of strep throat
  • rapid flu tests – prone to false positive results if you test when flu activity is low
  • thyroid function tests
  • monospot test – this is a non-specific test, so is not just for mono and most experts recommend that it no longer be used
  • EBV titers – titers of Epstein-Barr virus (EBV) antigens, including viral capsid antigen (VCA), Early antigen (EA), and EBV nuclear antigen (EBNA) can all appear at different points in your infection, from early on to years after you have recovered. Many persist for the rest of your life after you have had mono, which some folks confuse as a new infection or a relapse.
  • vaccine titers
  • ANA – while your anti-nuclear antibody test should typically be negative and a positive ANA can be a sign of arthritis, it is also very common for kids without any problems to have a positive or elevated ANA
  • WBC
  • vitamin D levels
  • drug testing
  • tox screening
  • covid-19 tests
  • EEGs

Why are these tests so easily misinterpreted?

False Positive Test Results

For one thing, many people underestimate the risk of false positive test results.

That’s why it is important to remember that a positive test doesn’t necessarily mean 100% that you have any specific disease or condition. It just means that you have a positive test.

“EEG will be negative in a large portion of patients with epilepsy, and may be positive in patients without epilepsy. False positive EEG findings commonly lead to unnecessary use of antiepileptic drugs and may delay the syncope diagnosis and treatment. EEGs are most helpful in specific situations when there is high pre-test probability for epilepsy based on history and exam, and clinical presentation.”

Do not routinely order electroencephalogram (EEG) as part of initial syncope work-up.

The fact that you can actually have a false positive EEG test should help you understand this whole issue a little better.

So how do you reduce the chance that you will have a false positive test result – or a false negative for that matter?

“A given test will have a higher positive predictive value in those patients with a higher prior probability of disease.”

Sensitivity, Specificity, and Predictive Values of Diagnostic and Screening Tests

You have to understand the sensitivity, specificity, and predictive values of the tests you use. And the things that influence them.

“The positive and negative predictive values vary considerably depending upon the prevalence of influenza (level of influenza activity) in the patient population being tested.”

Rapid Diagnostic Testing for Influenza: Information for Clinical Laboratory Directors

For example, when no one has the flu and disease prevalence is low, you are more likely to have false-positive rapid antigen test results. So that positive flu test this year, when no one has the flu might not actually mean that you have the flu either. It is probably a false positive, which makes you wonder why the test was done in the first place…

And know that you can’t just test everyone for everything…

More on Lab Tests That Are Often Misinterpreted

Does My Child Need a Flu Test?

Do you need to get a flu test if you think that you have the flu?

Your child has a fever, cough, runny nose, body aches and chills.

Should you rush them to your pediatrician for a flu test?

Diagnosing the Flu with a Flu Test

While you may want to seek medical attention, depending on your child’s age and how sick they are, believe it or not, you don’t need a flu test to get diagnosed with the flu.

“If your doctor needs to know for sure whether you have the flu, there are laboratory tests that can be done.”

CDC on Diagnosing Flu

A flu test is an option though.

Most people do not need a flu test.
Most people do not need a flu test.

Is it a good option?

A necessary option?

“Most people with flu symptoms are not tested because the test results usually do not change how you are treated.”

CDC on Diagnosing Flu

While a diagnosis of the flu can be made clinically, based on your symptoms, a flu test can be a good idea:

  • to help determine the cause of an outbreak (mostly if there aren’t already a lot of flu cases in your area)
  • if someone is at high risk for flu complications

In general though, most people do not need a flu test, especially during the active part of flu season.

What’s the problem with doing a flu test?

“In January 2017, the FDA reclassified antigen-based RIDT systems into class II. This reclassification was to help improve the overall quality of flu testing. The reclassification was prompted, in part, by recognition that the poor sensitivity of some of antigen-based RIDTs resulted in misdiagnosed cases, and, according to anecdotal reports, even death.”

FDA on CLIA-Waived Rapid Flu Test Facts

Mostly, they are neither as accurate nor as easy to interpret as most folks think, even the newer versions of these tests.

Have you ever heard someone say that they tested positive for both flu A and flu B?

When a flu tests is positive for both A and B flu strains, it invalidates the test. They may have had either flu A or flu B or neither, but they almost certainly didn’t have both.

The antigen-based rapid flu tests that most doctors and clinics use, which give results in 10 or 15 minutes, are also prone to both false positive (you don’t really have the flu, even though your test was positive), and more commonly, false negative (you actually do have the flu, even though your test was negative) results, depending if flu is active at the time.

Other flu tests are available, but are more expensive and take longer to get results, so aren’t used as often. These include “rapid” nucleic acid detection based tests that can be done in a doctor’s office, rapid nucleic acid detection based tests and rapid influenza diagnostic tests that are done in a central lab, PCR tests, and viral cultures.

So why do so many people rush to the doctor to get a flu test?

Many think that if they are positive, then they can take Tamiflu or another flu medicine and get better faster.

The problem with thinking like that is that few people actually need to take Tamiflu, as at best, it only helps you get better about a day quicker than if you didn’t take it. That’s why the recommendations for Tamiflu say to reserve it for children under two to five years of age and others who might be at high risk for flu complications.

Since most other people don’t need to take Tamiflu, they don’t necessarily need a flu test or a definitive diagnosis of the flu. Again, even if they did need Tamiflu, the diagnosis of the flu could be made clinically.

And even more importantly, a negative flu test doesn’t necessarily mean that you don’t really have the flu, especially if you have classic flu symptoms in the middle of flu season. Again, a negative flu test could be a false negative.

“RIDTs may be used to help with diagnostic and treatment decisions for patients in clinical settings, such as whether to prescribe antiviral medications. However, due to the limited sensitivities and predictive values of RIDTs , negative results of RIDTs do not exclude influenza virus infection in patients with signs and symptoms suggestive of influenza. Therefore, antiviral treatment should not be withheld from patients with suspected influenza, even if they test negative.”

CDC on Guidance for Clinicians on the Use of Rapid Influenza Diagnostic Tests

Have you ever had a negative flu test and the doctor still gave you Tamiflu? Then why did they do the test?

Diagnosing the Flu Without a Flu Test

If the results of flu testing aren’t going to change how you are treated, then you probably don’t need to have the flu test done in the first place.

Plus it saves you from having a swab stuck up your nose.

But kids should have flu tests, right?

Although rapid flu tests might be a little more accurate in kids than adults, it is not by much, so you are left with the same issues.

A positive test might reassure you that it really is the flu, but your child could still have the flu if their test is negative. A diagnosis and treatment decision can be made clinically, without a flu test, remembering that most older, healthy kids don’t need to be treated with Tamiflu.

We can’t skip flu season (although we sure can try if we get vaccinated and protected), but we can try and skip flu testing season.

More on Flu Tests

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