Paroxysmal cold hemoglobinuria: a difficult diagnosis in adult patients.

Background: Paroxysmal cold hemoglobinuria (PCH) is a rare form of autoimmune hemolytic anemia caused by a biphasic (Donath-Landsteiner [DL]) immunoglobulin G autoantibody. Estimates of disease frequency after syphilis are lacking and the diagnostic yield of testing for PCH is uncertain. The objectives of this study were: 1) to describe DL testing practices in Canada, 2) to determine how often a biphasic RBC antibody is detected in adults and children, and 3) to evaluate inter-rater reliability of interpretations of positive DL test results in adults.