Most severe neutropenia in individuals with no chronic condition did not result in a specific diagnosis.

Background And Objectives: This study estimated the incidence of unexplained severe neutropenia (neutrophil count 500 x 10(6)/L) and hospitalized morbidity in the year after a finding of severe neutropenia in persons 2 years of age or older based on clinical laboratory data.

Methods: Computer-stored data from the Kaiser Permanente Laboratory Management System/Results Management System were used to identify findings of severe neutropenia in members of Kaiser Permanente Southern California 2 years of age or older during the period January 1, 1997, through December 31, 1999. Computer record linkage and medical record review were used to exclude individuals with chronic disease or treatments with bone marrow toxic drugs known to cause neutropenia.