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.

Results: The incidence of findings of severe neutropenia was 47 per million persons per year (95% CI=42-53). Only 11% of individuals with a finding of severe neutropenia were hospitalized with neutropenia diagnosis. The hospitalization rate for infection occurring within 1 year of severe neutropenia was 3.2% (95% CI=1.5-6.2%).

Conclusion: Most laboratory findings of severe neutropenia in individuals with no chronic condition do not result in a specific diagnosis. In a population-based sample of findings of severe neutropenia identified by laboratory testing, hospitalization for infection was rare.