Using direct antiglobulin test results to reduce unnecessary cold agglutinin testing

BACKGROUNDCold agglutinin disease (CAD) is a rare autoimmune hemolytic anemia mediated by autoantibodies that preferentially react at 4 degrees C. Laboratory testing for cold-reactive autoantibodies is laborious and may not be ordered judiciously, particularly in patients with a negative direct antiglobulin test (DAT). We sought to determine whether a negative DAT using anti-human complement (anti-C3) rules out elevated cold agglutinin (CA) titers and the diagnosis of CAD. STUDY DESIGN AND METHODSWe performed a retrospective study of patients with a CA test performed at three major academic medical centers: Barnes-Jewish Hospital (2003-2014), Vanderbilt University Medical Center (2007-2009), and Massachusetts General Hospital (2009-2014). RESULTSThis study included 801 patients, of whom 51% (n=410) had a DAT within the 7days before CA testing. A total of 98% of patients with a negative DAT using anti-C3 had a negative CA titer (<64). Only five subjects had a negative DAT using anti-C3 and an elevated CA titer. CONCLUSIONSOverutilization of CA testing could be reduced by establishing laboratory acceptance criteria based on a positive DAT using anti-C3. Such acceptance criteria would have reduced CA testing by 68% for those with an available DAT result.