As the sample migrates along the assay it first encounters a conjugate, usually colloidal gold, which is labelled with antibodies specific to the target analyte. If the target analyte is detected within the sample the conjugate antibodies will bind and subsequently reach the test line which also contains antibodies specific to the target. Once the sample reaches the test line and the target analyte is present a visual change, normally a line appearing, will occur allowing the test to be read as a positive.