What precisely is a lateral flow test (LFT)?
A lateral flow test (LFT) is a simple, fast, and inexpensive assay for detecting the presence of target antigen(s) or antibody(ies) in a liquid sample. 1 As a type of immunoassay, detection relies on antibody binding to their target antigen in conjunction with a detection reaction to produce a readable, often visible, result.
How to Interpret a Lateral Flow Device (LFD)
Many LFTs can be read by eye because the majority of tests produce a visible result with lines developing where the conjugate, with or without the target, is captured. The presence of the control line indicates successful testing with direct assays, and the presence or absence of the test line indicates a positive or negative result . Another type of LFT, the competitive test (discussed further below), necessitates a different interpretation of results. Although not commonly used by the general public, it is critical to determine what type of test you are evaluating.
It is critical to remember that results should only be interpreted within the timeframe specified for that specific test. If they are read too soon after the sample is introduced, the result may not have had enough time to fully develop. If the reaction is left too long after the sample is introduced, the bands may change over time as the reaction deteriorates or overdevelops.
The Strengths of lateral flow assays
LFTs have a number of advantages that have led to their widespread use, not least in applications such as pregnancy testing and the COVID-19 pandemic. However, as with most assays, there are limitations12 to their use, which are summarized below.
Cheap
Quick turnaround time (normally minutes)
Portable, especially those that can be read with the naked eye
Can usually be kept at room temperature, making it ideal for point-of-care and home testing, as well as testing in remote areas where refrigeration may be difficult or inconsistent.
Generally, they have a long shelf life.
For the most part, no electricity is required.
A variety of digital readers are available to suit various settings.
Small sample volumes are required.
Readers can improve the precision with which results are interpreted and recorded.
Multiplexing is possible.