Passive agglutination test: It is similar tohaemagglutination test but the physical nature of thereaction is altered.The Ag is coated on the surface of a carrier particleand thereby helps to convert a precipitation reactioninto an agglutination reaction making the reactionmore sensitive. The carrier particles used can be RBC,latex particles or bentonite. Some times RBC coatedwith polystyrene (tanned RBC) can be used.When patients serum is mixed with these, it leads toagglutination. This test is used for the diagnosis ofRheumatoid arthritis