Spurious automated leukopenia due to in vitro granulocyte aggregation.

A patient with spurious automated leukopenia secondary to in vitro aggregation of neutrophils is evaluated. The primary importance of this transient phenomenon is the potential generation of unnecessary clinical investigation and diagnostic expense. The cause of this phenomenon is not related to time, temperature, or type of anticoagulant. The true leukocyte count is obtained easily by diluted manual leukocyte counts. Presence of granulocyte aggregates on anticoagulated blood smears should suggest spurious leukopenia, and smears of anticoagulated blood should be examined in patients with unexplained leukopenia.