You can spot the difference between valid and invalid FlowFlex test kits by checking the Lot number on the side of the box. (Philadelphia Department of Public Health)

If you recently picked up an at-home COVID test kit in Philadelphia, check the box.

A batch of what was marked as Flowflex COVID-19 Antigen Home Tests has been found to be invalid, according to the city Health Department, which on Saturday afternoon sent out a press release about the discovery.

How can you tell if you have one? Look at the label on the long, skinny side of the box. If the lot number says “COV2110012,” toss it in the trash.

You can pick up a free replacement at a city health center or several other locations across the city.

The issue was discovered during a routine inventory check, according to the Health Department, when one of the lot numbers recorded came back as unknown. The FDA maintains a database of authorized at-home tests, specifically to help people avoid counterfeits, and the unknown number was not among them. 

A total of 105,000 kits were found to have been declared invalid by the manufacturer, per health officials. They’re not entirely sure how many were actually taken home by residents, because a lot of them get distributed through partner organizations. About 4,000 were distributed directly through the Health Department. 

The recall was issued because unauthorized tests might not give accurate results, department spokesperson James Garrow told Billy Penn.

“We’re assuming that it would be impossible to know for sure if the results were incorrect, so we’re recommending folks throw them away and pick up new ones, just to be sure,” Garrow said.

The valid and invalid FlowFlex test kits look very similar on the front of the box. (Philadelphia Department of Public Health)

Health Commissioner Cheryl Bettigole reiterated that having trustworthy tests is critical.

“One of the most important things that Philadelphians can do to prepare their families for the fall and winter COVID season is to have at-home testing kits on-hand,” Bettigole said in a statement. “It’s important to have faith in those tests, so we want to make sure that every test out there is valid and correct.”

Counterfeit tests have been circulating around the U.S. for years. The FDA and FTC formed a cross-agency task force to monitor for fraudulent products back at the start of the pandemic. 

In spring 2022, as over-the-counter rapid tests became commonplace at pharmacies and drug stores, the agencies ramped up enforcement and added a page about counterfeit tests to the FDA website. 

What happens if you or someone you know used one of these tests? 

It’s not like you’re in immediate danger, like if you ate meat or lettuce recalled because it might carry disease. The risk, according to the FDA, is that you might get inaccurate results. 

If there’s a false negative, you could unknowingly spread the virus and not get treated for COVID as soon as you might have otherwise. 

If you have symptoms and end up with a false positive, that could delay the proper treatment for whatever sickness you do have — or end up with you unwittingly exposing yourself to someone who is actually positive, since you might not take the same precautions to isolate from them.

The Philadelphia Health Department is currently going through its entire inventory to double-check all the lot numbers, according to city officials. The invalid tests came from a longtime vendor, so the department is also working on developing new procedures that would confirm tests are authorized before they get shipped to Philly.

After months at all-time lows, COVID cases and hospitalizations inched upward at the end of August, both across the nation and in Philadelphia. However, the numbers are still among the lowest since the pandemic hit.