Principles of Flow-through test

A flow-through test or immunoconcentration test  is a diagnostic test that allows the user to test a sample such as blood for the presence of a biomarker, usually a specific antibody.They are a point-of-care test, a test intended to be used by healthcare providers when they come into contact with patients.Point-of-care tests often allow rapid detection of specific biomarkers without the need for specialized laboratory equipment and training; this facilitates diagnosis and allows for faster initiation of therapeutic action.The flow-through test was developed in the early 1980s as the first immunostrip to be developed, although the lateral flow test subsequently became the primary immunostrip care device.

Principle of flow-through tests 

Flow analysis is in principle conjoint analysis.In practice, they are mainly used to detect antibody interactions, such as the interaction of antibodies from a test subject's blood sample with immobilized antigens, resulting in the formation of antigen-antibody complexes.However, other types of capture-assays are technically feasible, including small molecule capture assays or antigen tests.The flow-through test usually comes in the form of a box which is divided into four parts: the upper shell, the reaction membrane plate, the absorber plate and the lower shell.To perform the test, a diluted sample is applied to a reaction membrane panel and flows through an absorbent pad, where the target analyte is trapped in the membrane.The membrane is then washed to remove unbound non-target molecules, washed again with a solution containing the signaling reagent, and then washed again to remove unbound signaling reagent. If the analyte was present in the original sample, then at the end of the process it should bind to the membrane and the signaling reagent binds to it, revealing (usually visually) the presence of the analyte on the membrane.

Advantages and disadvantages

Flow tests can be performed faster than lateral flow tests.They show good sensitivity for antibodies but their detection of antigens is generally not as sensitive as lateral flow tests.