A rapid cold agglutinin test in Mycoplasma pneumoniae infection.

A definite diagnosis of Mycoplasma pneumoniae infection is currently based on cultural method or complement fixation test which is usually retrospective. A rapid cold agglutinin test was developed to determine its value on the early diagnosis of M. Pneumoniae infection. One hundred and thirty patients with pneumonia aged between 5 and 14 years were studied. Blood specimens from all the patients were collected for rapid cold agglutinin test, cold hemagglutination test, and complement fixation test. Thirty patients showed positive, rapid cold agglutinin test. All the patients with positive rapid cold agglutinin test had higher (greater than or equal to 1:32) cold agglutinin titers which were simultaneously performed. The rapid cold agglutinin test had 100% sensitivity and 97% specificity when a cut-off criterion was set at cold agglutinin titer greater than or equal to 1:64. Twenty-five of the 130 cases were serologically proven to have M. pneumoniae infection using complement fixation test or/and cold agglutinin titer. M. pneumoniae was a major cause (21/28) in cold agglutinin-positive pneumonic patients. The positive predictive value of the rapid cold agglutinin test is 70% (21/30). Only 28% (7/25) of the patients with M. pneumoniae infection were diagnosed at acute stage with serological method. We conclude that the rapid cold agglutinin test is of much value in the early detection of M. pneumoniae infection in office or hospital practice in children with pneumonia.