Here's what the letters C and T mean on a rapid test — and why they're used

If you're one of the thousands of New Brunswickers who picked up a COVID-19 rapid test kit, you might be wondering what those letters for negative and positive mean.

If your antigen test result reveals a letter C — you're in the clear. 

That line stands for control and means the virus wasn't detected, while the other indicator is "T" for test.

The kits handed out in New Brunswick follow an industry standard for infectious disease testing, according to the company that makes them.

Free rapid tests for home use are being offered province wide. They're manufactured by BTNX Inc., a Markham, Ont.-based company with operations around the world. It creates medical devices for many medical conditions, ranging from cancer to pregnancy.

Khasim Ali Khan, the technical operations manager, said those letters were used in the industry well before the pandemic.

"Not just for COVID, very much standard for any infectious disease rapid test," he said.

Reading the results

The kits use a result scheme of lines to reveal the results after about 15 minutes.

Khan, who oversees BTNX's regulatory applications, said there are a few possible result combinations to look for — including "invalid."

"If you see a test line, it means that there are the viral nuclear protein antigens in your specimen, which is supposed to be interpreted as a positive test result," he said.

A positive result: Two lines on control (C) and test (T).

Negative: One line on control (C).

Invalid: No lines or only a test line mean the results are invalid and it needs to be taken again.

Rapid test kits are available for free around New Brunswick. A full list of pickup locations can be found on the province's website.

Public Health says all positive rapid test results must be confirmed with a laboratory PCR test.