Another opportunity was recently offered to Americans to order free home coronavirus testing kits through the Postal Service. But because federal and state agencies have extended expiration dates for several brands of tests, it may not always be clear when free kits and other kits purchased separately will expire.

Although each box has an expiration date, meaning the test inside will no longer be reliable, the Food and Drug Administration has given emergency approval to extend the expiration date of several test kits as their manufacturers collect more data. Some states have also received FDA renewals for expired lab test lots or have approved their own renewals for federally authorized home tests. This means that some tests that expire in the coming weeks may still be used for several more months.

In January, the FDA granted Florida’s request for a three-month extension to rapid lab tests that had expired. In March, the California Department of Public Health emergency use approved home test kits past FDA-approved expiration dates. The general extension applies to all FDA-cleared over-the-counter tests, provided that each test’s control line—the line that is usually near the letter C—is clearly visible after the test is completed.

Extending the shelf life of a product is not uncommon. Manufacturers need time to demonstrate that a product is still working effectively after the initial expiration date, which is why many test kits have received renewals months after their initial approval. But some experts have expressed concern that the postponement and poor communication about the extension could create confusion.

“My concern is how the public will be informed about this?” said Michael T. Osterholm, an epidemiologist at the University of Minnesota. “Can they take boxes that are about to ship and put new expiration dates on top of the seal, for example? These are practical solutions.”

Some health departments published notices on their websites when a manufacturer is given an extension for its testing. But officials shouldn’t assume that everyone has Internet access or that they’re comfortable enough with a computer to look up this information, said Cindy A. Prince, an epidemiologist at the University of Florida.

“I think some people have realized that there are Covid tests that can be used after the expiration date on the test box, but they may not be aware that this does not apply to all Covid tests,” she added.

If a test kit has not received an authorized renewal from the FDA and the box says it has expired, some epidemiologists say it can still be used under certain conditions. According to Dr. Prince, most tests remain effective for some time if stored properly.

Annette Regan, an epidemiologist at the University of San Francisco, said that if no control line is visible on a test performed, the test should not be considered valid, regardless of the result.

FDA updates regularly life expectancy of home tests on your website. As of mid-June, these were the expiration dates of some popular test kits, according to the agency.

• BinaxNOW Covid-19 Ag Card Home Test (Abbott Diagnostics Scarborough, Inc.): Extended to 15 months from 12 months

• BinaxNOW Covid-19 Antigen Self Test (Abbott Diagnostics Scarborough, Inc.): Extended to 15 months from 12 months

• CareStart home test for Covid-19 antigen (Access Bio, Inc.): Extended to 12 months from 9 months

• Flowflex home test for Covid-19 antigen (ACON Laboratories Inc.): Extended to 16 months from 12 months

• BD Veritor Home Test for Covid-19 (Beckton, Dickinson & Company): 6 months

• Celltrion DiaTrust Covid-19 Ag Home Test (Celltrion USA, Inc.): Extended to 18 months from 12 months

• Cue Covid-19 Test for Home and OTC Use (Kew Health Inc.): 4 months

• Covid-19 Test Detection (Discovery, Inc.): Extended to 8 months from 6 months

• Ellum Covid-19 home test (Ellum Limited): 12 months

• iHealth Rapid Test for Covid-19 Antigen (iHealth Labs, Inc.): Extended to 9 months from 6 months

• SCoV-2 Ag Detect Quick Self Test (InBios International Inc.): Extended to 10 months from 6 months

• Lucira Check-It Covid-19 Test Kit (Lucira Health, Inc.): 6 months

• MaximBio ClearDetect home test for Covid-19 antigen (Maxim Biomedical, Inc.): 6 months

• Rapid Test InteliSwab Covid-19 (OraSure Technologies, Inc.): 9 months

• OHC Covid-19 Antigen Self Test (LLC “OSANG”): 8 months

• INDICAID Covid-19 Rapid Antigen Test at Home (PHASE Scientific International, Ltd.): 12 months

• QuickVue Home OTC Covid-19 Test (Quidel Corporation): 12 months

Alain Delaquerière contributed to research.