Lateral flow immunoassays have become increasingly popular point-of-care diagnostic tools because they are versatile, easy to use, and provide quick, accurate results without the need for laboratory testing. Most laypeople are familiar with lateral flow test kits in the form of at-home pregnancy tests, but the technology can also be used to diagnose illnesses and detect contaminants in food and water. But what exactly is a lateral flow immunoassay, and how does it work?

What is a lateral flow test?

Essentially, a lateral flow test gives visual indication of the presence of a certain chemical or chemical compound. Lateral flow tests can be used on a variety of sample types, including urine, saliva, serum, plasma, whole blood, sweat, water, and other fluids. They make up a staple of the point-of-care diagnostic test market because they don’t need to be sent to a laboratory to get the results. Lateral flow tests can be used in the field and in doctor’s offices and clinics and have become a primary way to detect disease biomarkers and infectious agents in the fields of clinical and veterinary medicine, agriculture, and food and environmental safety.

How does a lateral flow test kit work?

Lateral flow tests use a simple design consisting of a few standard pieces:

  1. Sample pad: This is an absorbent pad, often paper, onto which the sample to be tested is applied.
  2. Conjugate or reagent pad: This second pad generally contains antibodies specific to the analyte, or the chemical compound being measured. These antibodies are conjugated to colored or fluorescent particles (or labels), usually colloidal gold or latex microspheres. If the analyte is present in the sample, the antibodies and labels will bind to it and carry it along to the next layer of the test.
  3. Reaction membrane: This is generally a nitrocellulose membrane that acts as a test zone. The binding reagents on this membrane react with the analyte bound to the conjugated antibody. The presence of the analyte will create a colored test line. This membrane also contains a control line, which is essentially a quality control feature that indicates whether the sample liquid is passing through the strip properly.
  4. Reservoir: This final absorbent pad pulls the sample across the reaction membrane through a process called capillary action and absorbs any excess liquid.

All of these pieces are fixed onto a solid backing material. Lateral flow test kits typically come in the form of a plastic case with a sample port and a reaction window that shows both the test and the control lines.

Lateral flow test kits, like the IVD line of lateral flow immunoassays, are simple in design, easy to use, and require no special training or equipment. They provide a fast, accurate way for healthcare providers to diagnose illnesses like Giardia, Legionnaire’s disease, Cryptosporidium, and more.

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