Cold-induced granulocyte agglutination. A cause of pseudoleukopenia.

Transient cold agglutination of her granulocytes developed in a 60-year-old woman with a left upper lobe pneumonia during the acute phase of her illness. This phenomenon was manifested by pseudogranulocytopenia, multiple clumps of granulocytes on her peripheral blood smear, and abnormal distribution of granulocytes and monocytes on the white blood cell histogram when measured on an automated hematology analyzer (Coulter S-Plus IV, Coulter Electronics Inc, Hialeah, Fla). The cause is postulated to be an IgM autoantibody directed against components of the granulocyte membranes. Spurious leukopenia is encountered infrequently with automated hematology analyzers. Cold-induced granulocyte agglutination should be recognized as a potential cause of pseudogranulocytopenia so that white blood cell counts can be accurately reported and unnecessary evaluation of patients for leukopenia can be avoided.