Lateral flow tests are immunoassay tests that immobilize antigens in test lines on a strip of nitrocellulose. A sample being evaluated for the presence of an analyte that binds to the antigens in the strip is placed into a solution. The solution is dosed at one end of the test strip, and capillary action pulls the sample solution to the opposite end. While the fluid moves through the test strip, any analyte present in the sample solution will bind at the test line sites of antigens present on the stick. A colored line signals the active presence of the analyte in the sample solution.

Lateral flow testing can be used for the rapid and effective detection of a target analyte, such as a pathogen, toxin, human or animal biomarker, or food/water contaminant. Lateral flow tests can be done practically anywhere, making them great tools for on-site testing and detection. Lateral flow testing is especially useful in clinical and veterinary medicine, agriculture and dairy industries, environmental monitoring, forensics, and for laboratory research use. 

Learn more about uses for lateral flow testing by reading our Industrial Applications section below!

Lateral flow tests come in a large variety of shapes and designs, but almost all of them have similar features like test lines and control lines. Most test strips or cards are also fabricated with similar materials. Pregnancy tests are perhaps one of the most common lateral flow tests used by the general public.

Lateral flow assays typically have one or more control lines and at least one test line. Control lines always end up colored by the time the test has finished, regardless if the test is positive or negative for the analyte being investigated. Test lines, however, appear differently at the ends of tests based on the concentration of the analyte in the sample. Typically, test lines that are colored at the end of tests indicate that the analyte was detected in the sample solution.

Dipstick testing is a lateral flow testing format where a test strip is dipped directly into the sample solution being analyzed. The strip may also be placed in a strip holder prior to dosing with the sample. Dipstick tests are a simple in their design, efficient, and inexpensive. Its ease of use and common test line format has made it one of the most widely used and supported lateral flow testing formats.

A lateral flow cassette is an enclosure around one or many lateral flow test strips, often designed to make the test line regions the only visible areas of the strip(s). While there are commonly used cassettes, it is also common for many test strip and lateral flow reader manufacturers to create their own cassettes to work specifically with their product.

Lateral flow tests can be used as antigen tests. Antigens are molecules attached to the surface of cells, viruses, or bacteria that can produce an immune response. In this case, they are placed inside lateral flow test strips to recognize bacterial or viral pathogens. 

Lateral flow antigen tests reveal if a target pathogen is present in a particular sample. If the target pathogen is detected, antibodies will bind to the target and produce a colored test line(s) on the dipstick, signifying the presence of the pathogen.

Lateral flow tests can be used to detect viral infections, such as the ones used to detect COVID-19. Not all lateral flow tests reveal if a sample currently has a viral pathogen – pregnancy tests, for example, determine if someone is currently pregnant.

While not necessary, it is common for lateral flow manufacturers to operate in accordance with International Organization of Standardization (ISO) standards, specifically ISO 9001 and ISO 13485. Abidance by these standards ensures the company’s products/services meet customer expectations and follow the applicable statutory and regulatory requirements. It is important to note the difference between abidance to ISO standards and certification; companies can purchase the ISO standard from an ISO vendor to help design their product, while certification entails the company’s product has undergone third-party testing to verify it conforms to the ISO standard.

Some lateral flow tests and readers may have specific standardization requirements or regulations from governments based on the industry the test is used in. In the United States, for example, lateral flow readers used in the medical industry must be compliant with 21 CFR Part 820, a Food and Drug Administration (FDA) regulation that applies to all medical device manufacturers operating in the United States. 

Yes, lateral flow tests will expire after their designated shelf life period ends. Lateral flow tests should be kept in the conditions specified by the manufacturer to ensure the tests remain viable until their expiration date.

An assay reader is an optical device that analyzes an assay test, most specifically immunoassay lateral flow tests, by taking a picture of the resulting signal. A lateral flow reader is required to analyze the results of advanced qualitative and quantitative test types. In a lateral flow reader, the camera measures the intensity of color produced at the test and control lines, compares these intensities to the empty white region on the strip, and displays a result based on quantitative analysis.

Detekt Biomedical offers a universal and customizable lateral flow reader in our RDS-2500 product. Equipped with a standard track for dipstick testing, the option to get a customized track designed to perfectly fit your unique cassette, and built-in support for qualitative, semi-quantitative, and fully quantitative lateral flow tests. 

Immunoassays are used to detect the presence of analytes (proteins, hormones, antibodies, toxins) in a sample through the binding of antibodies and antigens. This technology can be used to detect particles and contaminants in samples, crucial for prevention and diagnostics in a variety of industries.

Colloidal gold nanoparticles are used for a wide array of biological labeling and optical imaging purposes. It is commonly used in lateral flow tests (LFT) and lateral flow assays (LFA). Immunochomratograhpy assays use colloidal gold as the visual signal indicators. The process of analyte presence and binding is detected by the resulting pink lines that appear.

As the lateral flow rapid assay industry grows, the need for quantitative results increases. Departments such as the FDA require documentation of values other than positive/negative results for testing and product development. In order to validate results, a lateral flow reader is needed. Some lateral flow assays are developed and validated using a lateral flow reader. Other companies use the readers to read, store, and analyze their lateral flow strip results. 

At the highest concentration of an analyte sample, the concentration will be lower due to the Hook Effect. The signal is similar to a lower concentration. In lateral flow testing, this effect can produce a false negative when there are high concentrations of sample present. This leads to a need for quantitative testing, with asymptotic bounds and timed testing.