Ultrasensitive latex-agglutination-test for the specific immunochemical detection and quantification of faecal occult blood loss.

Latex agglutination was used for the development of a simple and fast immunochemical faecal occult blood test which is ultrasensitive and specific for human haemoglobin. "In vitro" detection limits of 0.0002 and 0.003 ml blood/100 g stool homogenate were obtained for the tube and filter versions of the latex-agglutination test. The quantification of the blood content in stool homogenates is possible by diluting the haemoglobin containing faecal extract until no more agglutination occurs. Considering the nonuniform distribution of blood in faeces "in vivo" sensitivities of greater than 0.002 and greater than 0.03 ml blood loss/day respectively can be expected for the tube and filter versions of the latex agglutination test. This test is about 10,000 times more sensitive than the unspecific chemical guaiac type occult blood tests and at least 1,000 times more sensitive than other immunochemical occult blood tests which use immunofluorescence, radial immunodiffusion or an enzyme immunoassay. Nuclear medical reference methods like 51Cr faecal excretion or 59Fe whole body retention cannot be used for the calibration of the ultrasensitive latex agglutination test since they are not specific for blood losses below 3 (51Cr) and 5 (59Fe) ml/day.