25 October 2026
CareFree Kits editorial · General educational information
How rapid tests actually work
Two lines, one line, no lines. Here is what is happening inside a rapid test device.
Lateral flow, explained A rapid test uses a strip that draws your sample along it. Antibodies fixed to the strip catch what the test is looking for and produce a coloured line.
The control line The C line shows the test itself has worked. If there is no C line, the result cannot be trusted, whatever else you see, and the test must be repeated with a new kit.
Faint lines A faint test line is still a line. Read it in good light and treat it as a result to follow up with a healthcare professional.
Timing is part of the test Reading too early or too late can give a wrong answer. Use a timer and read the result inside the window given in your kit instructions.
This article is general health information and does not replace professional medical advice. If you have symptoms, or a result you are unsure about, speak to a doctor, GP or sexual health clinic.