Methods for detecting antigen-specific antibodies in a biological sample are described. The disclosed methods can be used for the diagnosis of a variety of autoimmune and infectious diseases. The methods use a neodymium magnet to efficiently isolate immune complexes. The disclosed methods are rapid, highly specific and sensitive, require very small volumes of biological sample, and do not require the use of radioactivity. With these advantageous features, the disclosed methods are amendable for point-of-care testing (POCT), which is currently not available for the detection of autoantibodies associated with autoimmune disease or for the detection of many pathogen-specific antibodies.