In this sample, the Hgb and Hct have failed the correlation check, and the red cell indices in this individual are astronomically high and have been flagged by the automated instrument. The most likely explanation for these results is the development of a strong cold agglutinin in the patient's sample. Cold agglutinins or cold antibodies were first described by Landsteiner in 1903 and are usually IgM in origin. These agglutinins may occur as a primary anemia or a secondary development to a primary disorder. Individuals who have cold agglutinin disease are usually elderly and have a

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30 Part I • Basic Hematology Principles


chronic hemolytic anemia combined with extreme sensitivity to cold temperatures leading to Raynaud's syndrome. These individuals may bind complement at colder temperature and hemolyze, causing a decreased Hgb and Hct. Agglutination in the digits and extremities may cause vascular obstruction and lead to acrocyanosis. In many cases, relocation to a warmer climate results in far fewer hemolytic episodes. Secondary cold agglutinins are observed in individuals with infectious mononucleosis, anti-mycoplasma antibodies, cytomegalovirus antibodies, malaria, anti-hepatitis antibodies, and HIV antibodies. In each of these cases, the immune system is compromised and sets the conditions for the development of an autoantibody against the patient's cells. The resolution of the CBC is to warm the sample in a 37°C water bath for a prescribed amount of time according to laboratory proto col. The sample is then recycled through the automated instrument, and the results are compared and then reported. If the cold agglutinin persists, the sample may need to be warmed for a second time to allow the results to equilibrate within reportable range. The CBC results show the patient's results after a 30-minute warming:

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