A method of screening a sample of body fluid for distinct populations of at least first and second autoantibodies which respectively bind at least first and second distinct antigens, which method comprises:
- (a) providing at least first and second antibodies to said at least first and second distinct antigens, wherein said first and second antibodies are immobilized at first and second discrete detection positions on a substrate;
- (b) providing one or more sources of said at least first and second distinct antigens, wherein said first antigen comprises a binding site to which either said first autoantibody or said first immobilized antibody binds, and said second antigen comprises a binding site to which either said second autoantibody or said second immobilized antibody binds;
- (c) contacting said at least first and second antigens of step (b) with said sample of body fluid, so as to obtain a mixture wherein said first and second antigens respectively bind with said first and/or second autoantibodies when present in said sample of body fluid;
- (d) allowing said mixture obtained in step (c) to flow along said substrate of step (a) to said first and second antibodies immobilized at said first and second discrete detection positions on said substrate;
- (e) providing labeling means directly or indirectly to said first and second antigens respectively so as to enable the presence of said autoantibodies in said sample of body fluid to be detected;
- and
- (f) monitoring binding of said first and second antigens with either said first and/or second autoantibodies, or said immobilized antibodies, by detection of the absence or presence of said directly or indirectly labeled first and second antigens at said first and second discrete detection positions on said substrate, so as to provide an indication of the presence of said autoantibodies in said sample of body fluid, wherein said first and second autoantibodies when present in said sample being screened bind with said first and second antigens when a mixture is obtained in step (c), whereby subsequent respective binding of said first and/or second immobilized antibodies with said first and second antigens in step (d) is completely or partially inhibited;
- wherein
- (i) in the absence of said first autoantibody said directly or indirectly labeled first antigen is detectable at said first discrete detection position on said substrate;
- or
- (ii) in the presence of said first autoantibody said directly or indirectly labeled first antigen is not detectable at said first discrete detection position on said substrate, or is detectable at said first discrete detection position at a reduced level compared to (i);
- and
- wherein
- (iii) in the absence of said second autoantibody said directly or indirectly labeled second antigen is detectable at said second discrete detection position on said substrate;
- or
- (iv) in the presence of said second autoantibody said directly or indirectly labeled second antigen is not detectable at said second discrete detection position on said substrate, or is detectable at said second discrete detection position at a reduced level compared to (iii).