[False positive FDP test associated with malignant lymphoma].

We present a man with non-Hodgkin's lymphoma who had false positive FDP test results and who had monoclonal IgM and IgG. At admission, laboratory examinations showed elevated FDP levels and prolonged PT and APTT, which did not improve by anti-coagulation therapy. Although coagulation system data returned to normal levels after steroid pulse therapy, the FDP level increased. Positive pregnancy test and results of dilution analyses on FDP assay yielded a diagnosis of false positive FDP test results due to serum latex agglutinin. The addition of anti-immunoglobulin antibody inhibited latex agglutination by serum. FDP levels positively correlated with serum IgM concentrations. These data suggest that the false positive FDP test in this case was due to latex agglutination by monoclonal IgM.