In the Lab: How do Lateral Flow Tests really work?

Lateral Flow Tests (LFTs) have become part of everyday life, but the science behind them is often less well understood. At SureScreen Diagnostics, we design and manufacture these tests – here’s a closer look at how they actually work.

1. Capturing the target

Every test begins with a sample – saliva, blood or urine swab material. The fluid travels through a highly porous nitrocellulose membrane, where antibodies are embedded. These antibodies are designed to capture a specific “target” antigen, such as a virus protein or drug metabolite.

2. Making the invisible, visible

To show whether the target is present, lateral flow tests use gold nanoparticles. These nanoscale gold spheres are inert, safe to handle and produce a distinctive red colour. When attached to detection antibodies, they bind to the target and create the visible red line that signals a positive result.

3. The Control Line – what it really means

Every test includes a control line to show that liquid has flowed correctly through the strip. Importantly, this line doesn’t confirm that the sample was collected properly, that the right buffer was used, or that the test result itself is valid – it simply confirms the chemistry inside the strip is working.

4. Accuracy, sensitivity and specificity

• Sensitivity measures how well a test correctly identifies positives
• Specificity measures how well a test correctly identifies negatives
• Accuracy combines both into an overall measure

However, context matters. A highly accurate test in a low-prevalence setting can still produce many false positives, while a lower-sensitivity test in a high-prevalence outbreak may be more effective for rapid screening.

The bottom line

“Good” statistics don’t automatically make a test useful, and “weaker” statistics don’t always mean a test is poor. What matters most is using the right test in the right situation.

At SureScreen Diagnostics, we bring scientific rigour and decades of experience to the development of lateral flow technology, ensuring tests perform in real-world settings, not just in the lab.