Incidence of Clinically Relevant Solitary Pulmonary Nodules Utilizing a Universal Health Care System

INTRODUCTION: Solitary pulmonary nodules (SPNs) are common, but the clinical relevance of these nodules is unknown. Utilizing current screening guidelines, we sought to better characterize the national incidence of clinically important SPNs within the largest universal health care system in the nation. MATERIALS AND METHODS: TRICARE data were queried to identify SPNs for ages 18-64 years. SPNs that had been diagnosed within a year with no prior oncologic history were included to ensure true incidence. A proprietary algorithm was applied to determine clinically significant nodules. Further analysis characterized incidence by age grouping, gender, region, military branch, and beneficiary status. RESULTS: A total of 229,552 SPNs were identified with a 60% reduction seen after application of the clinical significance algorithm (N = 88,628). The incidence increased in each decade of life (all P < 0.01). Adjusted incident rate ratios were significantly higher for SPNs detected in the Midwest and Western regions. The incident rate ratio was also higher in females (1.05, confidence interval [CI] 1.018, P = 0.001) as well as non-active duty members (dependents = 1.4 and retired = 1.6, respectively, CIs 1.383-1.492 and 1.591-1.638, P < 0.01). The incidence calculated per 1,000 patients overall was 3.1/1,000. Ages 44-54 years had an incidence of 5.5/1,000 patients, which is higher than the previously reported incidence of < 5.0 nationally for the same age group. CONCLUSIONS: This analysis represents the largest evaluation of SPNs to date combined with clinical relevance adjustment. These data suggest a higher incidence of clinically significant SPNs starting at an age of 44 years in nonmilitary or retired women localized to the Midwest and Western regions of the United States.