Scammers are selling bogus home COVID-19 tests. Here's how to avoid fakes.

With home COVID-19 tests at the top of Americans' shopping lists as the Omicron variant continues to spread, scammers are trying to cash by taking advantage of unsuspecting consumers.

Earlier this month, the Federal Trade Commission warned that online criminals are posing as legitimate sellers of over-the-counter COVID-19 testing kits. "Unauthorized at-home testing kits are popping up online as opportunistic scammers take advantage of the spike in demand," the agency said.

The scams can take different forms. Some fraudsters pretending to be genuine merchants are hawking unauthorized rapid tests, while others have no merchandise on hand and just want to take your money and run.

"It's definitely happening and it's really challenging, depending on the sophistication of the scam, for the  consumer to discern this," said Gigi Gronvall, senior scholar at the Johns Hopkins Center for Health Security.

Senators Ed Markey and Richard Blumenthal are calling on the FTC to investigate reports of price gouging and other illegal practices surrounding the sale of over-the-counter at-home COVID-19 test kits.

In a letter sent to FTC Chair Lina Khan on Wednesday, the lawmakers said the surge in demand for at-home virus tests makes the current environment "ideal for predatory and profiteering behavior, including the sale of fraudulent test kits or charging exorbitant prices for those that are available."

Here are ways to make sure a COVID-19 test kit is legitimate and to avoid getting ripped off. 

Ensure the test is cleared for use by the FDA

Federal regulators have authorized only 13 home antigen tests on an emergency basis. The FDA has also authorized three molecular tests — also known as PCR tests and widely considered the gold standard of COVID-19 detection — that can be purchased without a prescription and administered by a layperson at home. You can check the name of the test for sale against the FDA's list of authorized kits, found here.

One reason for the strain on supply is that relatively few tests are FDA-authorized. Others got the green light but later had their authorizations revoked, making it harder for consumers to identify the most reliable tests.

"I've heard of a seemingly real company approaching a state with tests without a current Emergency Use Authorization. It might have had European approval, or it was given an EUA and then it was revoked. So the supplier actually had a piece of paper saying, 'This test was approved by the FD' — but they neglected to say two weeks later it was revoked," Mara Aspinall, a professor of biomedical diagnostics at Arizona State University, told CBS MoneyWatch.

"There are so many tests that have the European stamp of approval, and it's not that hard to get that mark. I worry that those tests won't be of good quality," Gronvall added.

Look for warnings about fraudulent products

The FDA also maintains an online database of warning letters it has sent to sellers of unauthorized or fraudulent COVID-19 products, including rapid tests.

In December, for example, the agency ordered DermaCare Biosciences of Delray Beach, Florida, to stop selling a product called the Easy Rapid Now COVID-19 Nasal Swab Antigen Test (Colloidal Gold) "without marketing approval, clearance or authorization from FDA.

Check the test's expiration date

Another growing scam involves sellers supplying authentic — but expired — rapid COVID-19 tests. Home test kits have short shelf lives — some expire within months. Experts warn that a test could deliver inaccurate results if it is administered past its use-by date.

Does it come with instructions?

Some COVID-19 test manufacturers sell batches of 25 or 40 tests directly to medical professionals, but not to consumers. The tests, which are intended only for professional use, are not packaged individually or in boxes of two containing instructions for use.

Buyers should look up the company's website and ensure their test kit includes all of the necessary components, including a full set of instructions. 

"We are finding some companies are buying boxes of 25 or 40 and then separating them and selling them at a premium. The pro box only has one set of instructions because it is happening in a doctor's office," Aspinall said. 

If the box says "for professional use," that's another red flag that could mean a seller isn't legitimate.