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With all the talk in the news at the moment about lateral flow tests, we take a look at what the lateral flow test is and what it can be used for. We also explain how lateral flow tests work and the different component parts that are used during the manufacturing process.

Common names for the lateral flow test

The lateral flow test is not always called the lateral flow test, different countries and different industries use various terminology to describe what these tests are – including:

  • Lateral flow test (LFT)
  • Lateral flow device (LFD)
  • Lateral flow assay (LFA)
  • Lateral flow immunoassay (LFIA)
  • Lateral dlow immunochromographic assays
  • Express test
  • Pen side test
  • Quick test
  • Rapud test
  • Test strip

What is a lateral flow test (LFT)?

So, with all that said, what is a lateral flow test? It is a simple to use diagnostic device that can be used to confirm either the presence or absence of a target substance, such as biomarkers in animals or humans, or contaminants in animal feed, food or water supplies. In fact, the most commonly used type of lateral flow test is the pregnancy test.

LFT’s typically contain a control line which is used to confirm that the test is working properly, as well as one or more test lines. These tests are designed to require minimal training in order to use them. The results can be read visually, or sometimes they provide data that is combined with reader technology.

Lateral flow tests, in general, are used across a wide range of industries for point of care testing. They can be performed by medical professionals, trained users or just by people themselves in a wide range of settings including a clinic, laboratory or the comfort of your own home. As they are part of the medical diagnostic industry, they are subject to regulatory requirements that must be adhered to for all products.

As they are such a versatile test lateral flow tests are used across a wide range of industry sectors including animal health, environmental testing, food and feed testing, pharma and plant and crop health.

How does the lateral flow test work?

Lateral flow tests (LFTs) rely on immunoassay technology based on nitrocellulose membrane, coloured nanoparticles and antibodies.

When a sample is added to the test the sample flows along the test device and passes through the conjugate pad into the nitrocellulose membrane and then on to the absorbent pad.

  • The first stage of the absorption process is the sample pad, and it sometimes contains a filter in order to ensure the controlled and accurate flow of the sample.
  • The conjugate pad which stores the antibodies and conjugate labels, then recieves the sample. If the taget is present in the sample, the immobilised conjugated antibodies and labels bind to the target and continue to move along the test
  • As the sample moves along the device the binding reagents bind to the target at the test line. A coloured line then forms with the density of the line varying depending on the quantity of the target that is present. Some targets may require quantification to determine target concentration which is when some tests are combined with a reader to provide a more quantitive result.
  • The sample then passes through a nitrocellulose membrane into an absorbant pad that absorbs the excess sample. The specification of this absorbant sample has an impact on the volume of sample that the test can incorporate.

Types of lateral flow tests

Lateral flow test can be used in a housed cassette format, or as a dipstick. Both housed cassettes and dipstick work in a similar way, so the choice of which is used will depend on the industry, the market requirement and the sample matrix.

The two main types of lateral flow tests available are:

  • Competitive assays – where a positive test is represented by the absence of a coloured line at the test line position
  • Sandwich assays – where a positive test is represented by the presence of a coloured line at the test line position

LFT Sample Matrices

The market requirement and the target analyte (substance) tend to determine what type of sample is used in the assay.

Some samples, such as animal feed, require a running buffer to aid sample delivery. Other samples, such as saliva, may be placed directly onto the test although there are occasions where a dilution buffer is required.

LFT Label Types

Lateral flow tests (LFTs) tend to use carbon, conjugated gold or coloured latex nanoparticles within the conjugate pad. Other types of labels include coloured polystyrene beads or magnetic beads.

Regardless of what label type is used they all perform the same function to create a three-way bond with antibodies and targets in order to make it visible the control and test lines.

Labels will be chosen during the development of the lateral flow test and will depend on factors such as the antibody, the sample matrix and the target. The optimisation of the assay will ensure the label interacts correctly with the antigen and antibody to ensure the efficiency and accuracy of results.

Quantitative rapid lateral flow test devices

When names such as quick test or rapid test can lead to myths around lateral flow tests, such as they are limited in their capacity and not accurate, but they are actually compact, easy-to-use and offer considerable flexibility.

Here at Fit2FlyTest, we offer lateral flow tests for travel for both UK Outbound and UK inbound flights, despatched for next day delivery (if ordered before 2 pm Monday to Friday).

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