The Power of Lateral Flow Immunoassays in Veterinary Diagnostics! Lateral Flow ImmunoAssays (LFAs) Dr. Sarah Maurice PhD. Clinical Advisor Introduction: In vitro diagnostic assays in the form of Lateral Flow ImmunoAssays (LFAs) first emerged in the commercial market in the 1970s and have since become a standard in the field of point-of-care rapid diagnostics. LFAs are commonly employed in veterinary hospitals and clinics to qualitatively confirm the presence of disease-causing pathogens (antigens) or for the detection of their antibodies. These test platforms have gained popularity because they are easy to use, have fast assay turnaround times, affordable prices, and are simple enough for non-specialized personnel to use. The primary advantage of using of LFAs in veterinary medicine is earlier detection and treatment as well as improved monitoring. This blog is intended to provide a general explanation of LFA technology as well as information that can be used as a guideline for choosing which tests to perform and how to incorporate the findings into the overall diagnostic scheme. Lateral Flow Assay Principles LFA While LFAs are simple and easy to use, their design is complex, requiring several different solid materials and sophisticated biochemical reagents. The reacting reagents of the test are typically housed within a plastic cartridge, and all that is required is to apply the sample followed by a compatible buffer. LFA technology is based on two principles: biochemical antigen-antibody interactions and the capillary movement of fluids through strips of porous materials. The sample (analyte) passes through multiple layers of filter membranes which are impregnated with specialized molecules that interact with the analyte being tested resulting in visually detected signals in the form of colored lines. The lines consist of a “control line” to confirm that the test is working properly and a “test line” which indicates target antigen-antibody interaction. Results which are determined by the presence or absence of the test line, are easy to interpret (positive, negative, or invalid) and are available after a short period of time (usually 10-30 minutes depending on the test). The advancement of LFA techniques has led to tests with better sensitivity and reproducibility. In addition, tests have been designed to detect multiple targets in a single run. Multiplex test cassettes show results for each target as a single control line with sequential test lines or in an array format, where multiple test strips are present within the cassette – one strip for each single target. Major types of LF test LFAs are available in two alternative platforms that can be used to detect either antigens or antibodies in biological samples. Depending on the test, a wide variety of biological samples are employed. Antigen detection tests target the organs most likely to contain the pathogen (urine, saliva, serum/plasma, excrement, and other tissues), as opposed to antibody detection LFAs that typically use EDTA-treated whole blood, plasma, or serum. Things to consider when deciding if a lateral flow test is rigth for your diagnostic practice When to choose an antigen and/or antibody Lateral Flow Assays? Antigen and antibody LFAs are carried out in similar ways but they serve distinct purposes and have different windows of opportunity. The antigen LFA recognizes the pathogenic organism when it is present in the body, making it most sensitive during the acute stage of the disease. A positive antigen test shows that the pathogen is present in the target organ indicating a current and active infection. The antibody detecting LFA test is used to identify whether the patient has generated target-specific antibodies during the course of an infectious illness (immunity). In certain diseases, particularly vector-borne, antibodies will circulate in the blood system for extended periods of time after the patient has recovered. For this reason, antibody tests should not be used to diagnose current or active disease. Advantage and disadvantage of LFAs When combined with the findings of a physical examination, anamnesis, and the results generated from a standard panel of hematology and biochemistry tests, lateral flow tests play a significant role in the diagnostic process. Antigen LFAs are ideal for initial screening and can assist in making quick treatment decisions. Results can confirm the presence or absence of a target pathogen and assist in making informed decisions on treatment. Antibody detecting LFAs may not directly detect active disease but should be used during the post-acute phase of a disease to more accurately identify the pathogen which caused the illness, for on-going management of a disease and for the assessment of the disease status. Lateral Flow Assays, similar to all in vitro diagnostic tests, are limited by their intrinsic levels of sensitivity. Their accuracy is contingent on proper tissue sampling as well as performing the test at the most appropriate stage of the disease. Pathogens, such as canine and feline Coronavirus, Parvovirus and Giardia duodenalis, target the digestive system but are shed intermittently in the feces during the disease process. For this reason, it is recommended that the test be conducted on three samples collected at regular intervals before arriving at a diagnosis. A negative result does not completely rule out the possibility of an infection. The stage of disease, at the time of sample collection, may have been outside the peak “shedding period” or the sensitivity of a particular test kit may have been below the level of detection for the pathogen in the sample. In such cases, alternative more sensitive diagnostic tests such as ELISA or PCR can be implemented. Point-of-care ELISA and PCR kits, suitable for use in veterinary clinics, are commercially accessible. Lateral flow immunoassays play an important role in infectious disease diagnostics. The technology allows the clinician to provide accurate point-of-care diagnostics at the time when the patient is present in the clinic, or even home settings. The addition of LFA diagnostics to the list of tests conducted for a patient can help corroborate the differential diagnosis in infectious diseases which have similar signs leading to rapid and accurate treatment plans. The takeaway is that point-of-care kits can streamline and enhance veterinary diagnostics. Whether you choose to use lateral flow, ELISA or/and PCR in your clinic, it is critical to purchase the products from a reputable company that is available to help you in selecting the best product for your specific needs. Notice: JavaScript is required for this content. About Sarah Maurice Sarah is the head of the Molecular R&D Department at Biogal Galed Labs Acs. She holds degrees in Animal Sciences, Fish Pathology and Biochemistry from McGill University, the University of Georgia and the Hebrew University of Jerusalem. She has filled positions as a Research Fellow in projects relating to molecular biology, protein engineering and recombinant vaccine development.
