Background: CAD is a complement-driven autoimmune hemolytic anemia in which IgM antibodies bind to red blood cells (RBC) at lower temperatures. Although exposure to cold may precipitate RBC agglutination, we recently reported a lack of seasonal variability in anemia, hemolysis, and healthcare utilization. Thromboembolic events (TE) are a newly reported but consequential complication of CAD. The effect of colder weather on TE risk is unknown. We therefore compared TE rates in CAD patients during all seasons in the US.

Methods: CAD patients diagnosed between 2009 and 2016 were retrospectively identified within the Optum clinical-claims database. TE were identified using diagnostic codes. TE risk was compared among seasons using logistic regression adjusted for age, sex, race, region, year, Charlson Comorbidity Index, and clustering within subjects.

Results: 808 CAD patients (63% female; 66% ≥65 years old) were identified. 204 CAD patients experienced 287 TE; 56 (20%) were in summer, 57 (20%) in fall, 79 (28%) in winter, and 95 (33%) in spring. Using summer as baseline, the adjusted TE risk was statistically higher in spring (odds ratio [95% confidence interval]: 1.60 [1.09–2.33]; P=0.016), but not in fall (1.06 [0.70–1.61]; P=0.785) or winter

(1.42 [0.96–2.12]; P=0.082).

Conclusions: Consistent with our previous CAD study demonstrating no significant impact of weather on hemolysis, these data further show no association between colder weather and TE. This suggests that CAD patients in the US may be at risk for TE year-long and should be monitored carefully during all seasons.