For lower-stakes COVID-19 checks, speedy antigen exams provide a fast and easy technique to display for SARS-CoV-2 at house. They are often notably useful if you recognize or suspect you’ve been uncovered to the coronavirus however can’t entry skilled testing (or await the outcomes).
FDA-authorized at-home antigen diagnostic exams can detect energetic COVID-19 infections, together with in asymptomatic people, in about quarter-hour. Total, these exams are much less delicate than molecular diagnostic exams executed in labs. Nonetheless, the outcomes of at-home antigen testing can present extra information—if not complete peace of thoughts—relating to one’s COVID-19 standing, particularly if you happen to take a look at continuously. Relying in your scenario, it could make sense to have a number of of those exams available.
Needless to say a destructive consequence doesn’t essentially imply somebody doesn’t have COVID-19, and these exams aren’t meant for use as the only real methodology of prognosis. “Antigen exams are an inexpensive and simple technique to determine an individual who could also be contagious,” stated Dr. Matthew McCarthy, an affiliate professor of drugs at Weill Cornell Medical School. For individuals with no recognized COVID-19 exposures, “if you happen to’re going to Thanksgiving, and there’s 20 individuals there they usually’re all absolutely vaccinated, you are able to do an antigen take a look at earlier than you go to ensure you’re not bringing the virus into the social gathering,” he stated, citing one potential use.
Taking a speedy antigen take a look at may also be applicable earlier than interacting with somebody who could also be extra susceptible to contracting the virus. “Even people who find themselves absolutely vaccinated could need to take one in every of these handy at-home exams earlier than going to spend time with Grandma, or no matter it could be,” stated Dr. Clare Rock, a medical epidemiologist at Johns Hopkins College College of Medication who runs a COVID-19 infection-control consultancy.
What’s good about these exams—and what’s not
At-home COVID-19 antigen exams are accessible and quick. Somewhat than ready for an appointment (or ordering a mail-in package and transport a pattern) after which ready for the outcomes of a molecular diagnostic take a look at, with an at-home antigen take a look at you may typically go from swab to lead to as few as quarter-hour. The exams are typically straightforward to carry out, and you may learn the outcomes manually (as with a house being pregnant take a look at) or digitally (with an app).
COVID-19 antigen exams are much less delicate than molecular diagnostics. Not like molecular diagnostic exams for COVID-19 that contain amplifying viral nucleic acids to the purpose the place they are often extra simply detected, antigen exams detect unamplified traces of virus and thus don’t decide up small indicators as readily. (Antigen exams are to not be confused with antibody exams, which are supposed to detect antibodies produced to answer the virus, and should not used for diagnostic functions.)
Though at-home antigen exams should not fail-safe, even molecular diagnostics just like the gold-standard PCR exams should not all the time correct relating to detecting energetic COVID-19 circumstances, since outcomes rely on, amongst different issues, the timing of the take a look at. When you’re swabbed too quickly after an publicity, you could take a look at destructive even in case you are carrying the virus. It’s also possible to obtain a optimistic PCR take a look at consequence after you’re now not infectious.
In contrast with molecular diagnostics for COVID-19, antigen exams are “not as delicate if we’re trying to perceive is there any even minute piece of virus current,” medical epidemiologist Rock stated, “however they’re very delicate if we’re trying to see is there a degree of the virus that now we have to be involved that any person may transmit to another person.”
How do totally different at-home COVID-19 antigen exams examine?
There are 9 SARS-CoV-2 antigen exams from 5 corporations now approved by the FDA for emergency use at house. These are variations of Abbott’s BinaxNow COVID-19 Antigen Self Take a look at, Entry Bio’s CareStart COVID-19 Antigen Dwelling Take a look at, Ellume’s COVID-19 Dwelling Take a look at, the InteliSwab COVID-19 Speedy Take a look at from OraSure Applied sciences, and the Quidel QuickVue At-Dwelling COVID-19 Take a look at. Of those, the Abbott BinaxNow, Ellume COVID-19 Dwelling, and Quidel QuickVue exams are at present out there direct to customers, with out a prescription, in pharmacies and on-line.
The directions that accompany all of those exams embrace a disclaimer that destructive outcomes could require extra testing for affirmation. For every of them, there’s a small probability of false optimistic outcomes, too.
The accuracy of an at-home antigen take a look at relies upon partly on take a look at sensitivity (the take a look at’s reported means to detect a real optimistic), take a look at specificity (its reported means to detect a real destructive), pattern integrity (whether or not a swab accommodates sufficient pattern or the swab resolution is contaminated by, say, one other pathogen), whether or not one follows the producer’s directions precisely, the time since an individual’s final recognized or suspected publicity and/or their onset of signs, and one’s viral load on the time of testing. (The exams are at present approved to be used on individuals as younger as 2, offered any youngster’s pattern is obtained and processed by an grownup.)
For a take a look at to be thought of for emergency use authorization, take a look at makers should undergo the FDA medical information demonstrating take a look at sensitivity and specificity. Some unbiased research have proven a lot decrease sensitivity and specificity for some antigen exams, notably once they’re used on asymptomatic people. (There’s one commercially out there SARS-CoV-2 molecular diagnostic take a look at at present approved by the FDA for emergency use completely at house, that means you don’t have to ship a pattern off to a lab for testing: the Lucira COVID-19 All-In-One Take a look at Package. It’s barely extra delicate—95.2%—in contrast with some FDA-authorized at-home antigen exams, and it offers ends in half-hour. However it’s at present unavailable on Lucira’s web site and at Amazon, the place it was as soon as bought.)
On the time of publication, at-home antigen exams have been laborious to search out as a result of a surge in COVID-19 circumstances prompted a spike in demand for them. When you’ve got bother discovering them on-line, name native pharmacies (these exams are sometimes stocked behind the entrance counter).
Abbott BinaxNow COVID-19 Antigen Self Take a look at
Sensitivity: 84.6% (PDF) (inside seven days of symptom onset)
Specificity: 98.5% (PDF) (inside seven days of symptom onset)
Exams included: two
Availability: Amazon, CVS, Walmart
The best way to take an at-home COVID-19 antigen take a look at
The important thing to getting reliable antigen take a look at outcomes is testing continuously. “Serial testing boosts sensitivity,” stated Christoper Brooke, an infectious ailments skilled on the College of Illinois at Urbana-Champaign. “The chances that you just’re going to check destructive twice whenever you’re contaminated are a lot decrease than the chances that you just’re going to check destructive as soon as.”
Somewhat than having a swab shoved up into the nasopharyngeal cavity, which you may encounter at a medical testing web site, the at-home antigen exams from Abbott, Ellume, and Quidel require a less-penetrative mid-nasal swab. Every take a look at comes with particular directions, which primarily require that you just swab your nostril, dip the swab into an answer, switch a number of the resolution right into a small reservoir, and await the consequence.
After quarter-hour or so, you may learn the outcomes of the Abbott BinaxNow and Quidel QuickVue exams very like you’d a house being pregnant take a look at: Two strains point out a optimistic consequence, and one line (the management) signifies a destructive. A really faint second line can nonetheless point out a optimistic consequence. The Ellume COVID-19 Dwelling Take a look at requires Bluetooth connection to a cellphone to supply ends in quarter-hour through a companion app (iOS, Android). In response to the corporate’s privateness coverage, Ellume should present public well being authorities with the person’s date of delivery and their state and zip code of residence, take a look at consequence, take a look at consequence date, and probably different data as required by legislation.
As is true for all COVID-19 diagnostics, together with PCR exams, the timing of pattern assortment in opposition to the final recognized or suspected publicity and/or symptom onset is the largest issue that may have an effect on the accuracy of at-home antigen take a look at outcomes. For this reason, for instance, Abbott’s BinaxNOW and Quidel’s QuickVue take a look at kits include two exams, supposed for use between two and three days aside.
“The sensitivity of a take a look at actually is determined by whenever you use it,” stated Daniel Larremore, an assistant professor of pc science on the College of Colorado Boulder who has modeled the consequences of repeated inhabitants screening of asymptomatic individuals with molecular and antigen exams. An contaminated individual’s viral load adjustments over time. “Once you attain a excessive sufficient viral load, antigens are going to be at a excessive sufficient focus to be detected.” Testing your self the day after attending a celebration with somebody who didn’t know that they had COVID-19 on the time is unlikely to be helpful. “Twenty-four hours after publicity, no take a look at goes to be optimistic,” Larremore stated. When you wait too lengthy to check, you could miss peak antigen focus, that means you need to see a fainter optimistic line if the take a look at detects SARS-CoV-2 antigens in your pattern.
“We sometimes suggest getting examined three to 5 days after publicity,” stated McCarthy of Weill Cornell. When you’ve got COVID-19–like signs, there’s no want to attend to check.
When to talk with a health care provider
Seek the advice of a doctor if you happen to’re uncertain of or confused by the results of an at-home COVID-19 antigen take a look at. Whether or not you need to search a confirmatory molecular take a look at is determined by your circumstances. One ought to deal with a optimistic antigen take a look at consequence as a real optimistic, stated Larremore, notably if extra elements—resembling a possible publicity or the looks of signs—assist the consequence. This implies isolating, alerting any contacts, and probably looking for to verify the consequence with a lab take a look at. Search medical remedy for signs as wanted. In response to Weill Cornell’s McCarthy, following up on a destructive antigen take a look at consequence with a confirmatory molecular diagnostic might not be crucial in circumstances the place somebody has a low suspicion of getting COVID-19 (for instance, they’re asymptomatic, absolutely vaccinated, and/or haven’t any recognized exposures).
Getting a lab-performed PCR take a look at is your finest wager for an correct COVID-19 prognosis, however appointments may be troublesome to get, and typically “it takes so lengthy to get the outcomes that they’re ineffective,” stated Brooke of the College of Illinois. “Ideally everybody would have frequent PCR testing with speedy outcomes reporting, however that’s clearly not attainable. Antigen exams are sometimes the one actually viable out there selection, to allow them to play a extremely essential function in rising the frequency of testing, and the breadth of testing, throughout the inhabitants.”