An immunoassay is a test that relies on biochemistry to measure the presence and/or concentration of an analyte. The analyte can be large proteins, antibodies that a person has produced as a result of an infection or small molecules. These assays are highly adaptable and can be applied to many formats depending on the needs of the end user. The principle component of an immunoassay designed to detect a specific analyte, such as influenza nucleoprotein, are the antibodies that have been carefully selected to ensure the detection of the analyte at low concentration with high specificity, meaning will not react with similar antigens. The second feature of an immunoassay is the system that is designed to detect the binding of the specific antibody to the target analyte. Originally the signal from an immunoassay resulted from an enzyme acting on a substrate to yield a colored solution with the amount of color in the solution being equivalent to the amount of antigen in the test solution.

More recently the many complex steps of an immunoassay have been compressed into a simplified format for the end user. The format is dependent on the flowing of the specimen together with the assay components through a nitrocellulose test strip. In this format, binding of the antibody to the target antigen is directly observable by the user due to the accumulation of dyed microbeads that will bind to a specific location on the nitrocellulose yielding a colored line that is easily observable by the user (if the target analyte is present in the specimen).

Immunoassays today are designed in many formats depending on the target analyte and the needs of the end user. They can also be used to detect target analytes in a wide range of sample types including serum, plasma, whole blood, urine, or swabs of nasal passages, throat or urogenital tracts.

Health Plus offers a continuum of diagnostic immunoassays including ELISAs, visually read rapid lateral flow tests and fluorescent immunoassays that are placed in an analyzer that automatically measures the fluorescent signals, interprets the data, and immediately displays the result on its screen.