Published online 14 October 2009
Haematologica, Vol 95, Issue 2, 270-275 doi:10.3324/haematol.2009.008417
Copyright © 2010 by Ferrata Storti Foundation

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Thrombosis

Hematocrit and risk of venous thromboembolism in a general population. The Tromsø study

Sigrid K. Brækkan¹, Ellisiv B. Mathiesen², Inger Njølstad³, Tom Wilsgaard³, John-Bjarne Hansen¹

¹ Center for Atherothrombotic Research in Tromsø (CART), Department of Medicine
² Department of Neurology, Institute of Clinical Medicine
³ Institute of Community Medicine, University of Tromsø, Norway

Correspondence: Sigrid Kufaas Brækkan, Center for Atherothrombotic, Research in Tromsø (CART), Department of Medicine, Institute of Clinical Medicine, University of Tromsø, N-9037, Tromsø, Norway. E-mail: sigrid.brakkan{at}uit.no

Background: Hematocrit above the normal range for the population, such as in primary or secondary erythrocytosis, predisposes to both arterial and venous thrombosis. However, little is known about the association between hematocrit and risk of venous thromboembolism in a general population.

Design and Methods: Hematocrit and related hematologic variables such as hemoglobin, red blood cell count, mean corpuscular volume, and baseline characteristics were measured in 26,108 subjects, who participated in the Tromsø Study in 1994–1995. Incident venous thromboembolic events during follow-up were registered up to September 1^st, 2007.

Results: There were 447 venous thromboembolic events during a median of 12.5 years of follow-up. Multivariable hazard ratios per 5% increment of hematocrit for the total population, adjusted for age, body mass index and smoking, were 1.25 (95% CI: 1.08–1.44) for total venous thromboembolism and 1.37 (95% CI: 1.10–1.71) for unprovoked venous thromboembolism. In category-based analyses, men with a hematocrit in the upper 20^th percentile (46% in men) had a 1.5-fold increased risk of total venous thromboembolism (95% CI: 1.08–2.21) and a 2.4-fold increased risk of unprovoked venous thromboembolism (95% CI: 1.36–4.15) compared to men whose hematocrit was in the lower 40^th percentile. The risk estimates were higher for men than for women both in continuous and category-based analyses. The findings for hemoglobin and red blood cell count were similar to those for hematocrit, whereas mean corpuscular volume was not associated with venous thromboembolism.

Conclusions: Our findings suggest that hematocrit and related hematologic variables such as hemoglobin and red blood cell count are risk factors for venous thromboembolism in a general population.

Key words: hematocrit, population range, arterial and venous thrombosis.

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High hematocrit as a risk factor for venous thrombosis. Cause or innocent bystander?

Anja J.M. Schreijer, Pieter H. Reitsma, Suzanne C. Cannegieter
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