Incidence of Neutropenia in Veterans Receiving Lung Cancer Chemotherapy: A Comparison of Administrative Coding and Electronic Laboratory Data

INTRODUCTION: The frequency of neutropenia associated with lung cancer chemotherapy outside of randomized trials is largely unknown because administrative coding underestimates its prevalence. This study compared International Classification of Diseases (ICD) diagnosis codes and electronic laboratory results, alone and in combination, for identifying neutropenia events. METHODS: Retrospective cohort study of 718 veterans receiving their first course of chemotherapy for non-small cell lung cancer. Incidence of neutropenia was assessed using electronic laboratory results and ICD-9 codes captured in the Department of Veterans Affairs (VA) electronic medical records (EMR). RESULTS: A total of 118 of 718 patients (16.4 percent) were identified with an absolute neutrophil count (ANC) less than 1,000 cells/mm(3), while only 49 of 718 patients (6.8 percent) had ICD-9 codes for neutropenia. Using the combination of laboratory results and diagnosis codes, 136 of 718 patients (18.9 percent) experienced a neutropenic event. Compared to laboratory results as a gold standard, diagnosis codes were specific (not present for individuals without a laboratory-documented low ANC), but not sensitive (missing for many individuals with a low ANC documented in their laboratory test results). CONCLUSION: Relying on ICD codes to identify neutropenia in administrative data likely results in under-reporting. The emerging availability of electronic laboratory results provides an opportunity to more accurately quantify patterns of neutropenia, identify individual risk factors, and assess clinical management practices—including use of colony-stimulating factor prophylaxis—in large community cohorts.