Check4® Haemoglobin is a rapid qualitative, immunochromatographic assay for the detection of faecal occult blood in colorectal cancer. The method employs a unique combination of monoclonal dye conjugate and polyclonal solid phase antibodies to selectively identify human haemoglobin with a high degree of sensitivity and specificity. After collection in a special collection device containing extraction solution, the sample is dissolved and the strip test is put into the extract. As the test sample flows through the absorbent pad, the labelled antibody-dye conjugate binds to the haemoglobin antigen forming an antibody antigen complex. The extract-colloidal gold mixture (antigen-antibody complex) moves by capillary action along the strip forming a line of immobilized complex at the antibody zone in the test region indicating the presence of haemoglobin antigen in the extract (pink coloured line). If no antigen is present the test zone will remain clear. Check4® Haemoglobin has an integral control feature. The appearance of a pink coloured line in the control zone of the test strip, formed of immobilized colloidal gold mixture, shows that the test has been carried out correctly.