Association between venous thromboembolism and air pollution in an industrial North American city: implications for anticoagulation management

Purpose: Emerging European evidence indicates that venous thromboembolism (VTE) occurs most often in winter. This suggests that VTE may be provoked by low temperatures or increased particulate matter (PM) pollution. In contrast to European cities, air pollution in many North American cities peaks in summer rather than winter. We hypothesized that analysis of temporal distribution of VTE in an industrial city (Detroit) with a summer pollution peak could resolve the role of these factors and offer insight into possible prothrombotic environmental effects.

Methods: Using ICD-9-CM codes, we identified 3,310 suspected VTEs in ambulatory patients at local emergency departments (2004-2008). VTE was confirmed by CT scan or sonography in 1,907 cases: the remainder served as comparators. We recorded demographic data, divided the cases by location (Detroit vs. suburban) and plotted the monthly VTE distributions. Using data from the Environmental Protection Agency, we determined the temporal distribution of different size categories of PM pollution. We compared distributions using circular statistics.

Results: Monthly Detroit VTE cases (1,490) exhibited a unimodal summer peak and differed from both a uniform distribution (P<0.01) and that of the 1,123 non-VTE cases (P<0.02). Levels of 10μm diameter PM and 2.5-10μm PM exhibited summer peaks versus a winter peak for 2.5μm PM. Temporal distribution of Detroit VTE cases differed from that of 2.5μm and 2.5-10μm PM (P<0.001), but not from 10μm PM (P>0.50). In contrast, suburban VTE cases (417) showed no monthly variation (P>0.20).

Conclusions: Our finding of a summer VTE peak in Detroit and close concordance with 10μm diameter PM indicates that low temperature is not a factor in VTE pathogenesis, but is consistent with a role for air pollution. Therefore, anticoagulation management should not only consider the patient, but also their environment; for example, patients living close to major roads and other PM sources may require increased surveillance.