© 2009 Schattauer GmbH, Stuttgart 676 The influence of meteorological variables on the development of deep venous thrombosis Helen K. Brown 1 ; A. John Simpson 2 ; John T. Murchison 3 1 Department of Community Health Sciences, University of Edinburgh, Edinburgh, Scotland, UK; 2 Department of Respiratory Medicine, University of Edinburgh, Edinburgh, Scotland, UK; 3 Department of Radiology, Royal Infirmary of Edinburgh, Edinburgh, Scotland, UK Summary The influence of weather on deep venous thrombosis (DVT) incidence remains controversial. We aimed to characterize the temporal association between DVT and meteorological vari- ables including atmospheric pressure. Data relating to hospital admissions with DVT in Scotland were collected retrospectively for a 20 year period for which corresponding meteorological re- cordings were available. Weather variables were calculated as weighted daily averages to adjust for variations in population density. Seasonal variation in DVT and short-term effects of weather variables on the relative risk of developing DVT were assess using Poisson regression modelling. The models allowed for the identification of lag periods between variation in the weather and DVT presentation. A total of 37,336 cases of DVT were recorded. There was significant seasonal variation in DVT with a winter peak. Seasonal variation in wind speed and tem- Keywords Deep venous thrombosis, venous thromboembolism, weather, atmospheric pressure, epidemiology perature were significantly associated with seasonal variation in DVT. When studying more immediate meteorological influences, low atmospheric pressure, high wind speed and high rainfall were significantly associated with an increased risk of DVT ap- proximately 9–10 days later.The effect was most strikingly dem- onstrated for atmospheric pressure, every 10 millibar decrease in pressure being associated with a 2.1% increase in relative risk of DVT.Alterations in weather have a small but significant impact upon the incidence of DVT. DVT is particularly associated with reduction in atmospheric pressure giving weight to the hypoth- esis that reduced cabin pressure in long haul flights contributes to DVT. These findings have implications for our understanding of the pathogenesis of DVT. Thromb Haemost 2009; 102: 676–682 Blood Coagulation, Fibrinolysis and Cellular Haemostasis Correspondence to: Dr JT Murchison Dept of Radiology Royal Infirmary of Edinburgh Little France Crescent Edinburgh EH16 4SU Scotland, UK Tel.: +44 131 242 3775 E-mail: john.murchison@luht.scot.nhs.uk Financial support: The University of Edinburgh paid £2,000 towards the cost of statistical analysis for this study. Received: April 3, 2009 Acepted after minor revision: June 16, 2009 Prepublished online: August 27, 2009 doi:10.1160/TH09-04-0214 Introduction In the US venous thromboembolism (VTE) has an estimated incidence exceeding 1 per 1000 of the population, contributing to over 50,000 deaths per annum (1).While a number of well de- fined risk factors for the development of VTE are recognised (such as immobility, recent surgery, recent fracture, pregnancy, malignancy and oestrogen therapy) the influence of meteoro- logical variables remains controversial. Pulmonary embolism (PE) has been associated with low at- mospheric pressure, low temperature, high rainfall, high relative humidity and high vapour pressure (2–6). The effects of me- teorological variables on deep venous thrombosis (DVT) are less well characterised. Overall, the emergence of a consistent effect of weather on VTE has been hampered by the requirement for large datasets to detect relatively small influences on the risk of VTE, and a tendency for previous, smaller studies to yield con- flicting conclusions. Scotland is a comparatively small country both geographi- cally and demographically (population approximately 5.1 mil- lion), with a relatively stable population, well-established me- teorological records and a centralised diagnostic coding system for hospital admissions. This combination presented us with the opportunity to make a detailed assessment of the associations be- tween DVT and variations in weather. The aim of this study was therefore to investigate the temporal association between DVT and meteorological variables, with particular emphasis on at- mospheric pressure.