Dehydration as a Possible Cause of Monthly Variation in the Incidence of Venous Thromboembolism

Abstract

Background: Monthly or seasonal changes in the incidence of venous thromboembolism (VTE) were previously reported; however, the mechanism of such variability is not completely understood. Methods: In the present retrospective single-center analysis, consecutive patients with proximal deep vein thrombosis and/or pulmonary embolism (PE) diagnosed between January 2009 and December 2013 were evaluated. Results: The study population included 1496 patients, 48% men, mean age 63 ± 18 years. Most (82%) cases with VTE were provoked and 39% of patients had active cancer. Four months of peak incidence (3, 7, 10 and 11) were compared with 4 months of the lowest incidence (4, 5, 6, and 12), showing a significant difference in VTE numbers (597 vs 405 cases/year, P = 0.001). In all subgroup analyses, including gender, provoked or unprovoked event and presence or absence of cancer, significant differences between the months of peak and lowest incidence remained. Blood urea nitrogen (BUN)–creatinine ratio was significantly higher in all cases in the peak incidence group compared to the lowest incidence group (24 ± 1.5 vs 21 ± 1.6, P = 0.03). In patients with unprovoked VTE (n = 269), levels of BUN and hematocrit were significantly increased in the peak incidence group compared to lowest incidence group (19.5 ± 0.8 mg/dL vs 16 ± 1.1 mg/dL, P = 0.03; 39.2 ± 0.3% vs 37.4 ± 0.5%, P = 0.01, respectively). Conclusions: The current study demonstrates that occurrence of VTE exhibits monthly variation also existing in patients with provoked events and even in those with cancer. Dehydration is suggested as a potential explanation to the month-related variation in incidence of VTE.