Hematocrit and the risk of recurrent venous thrombosis: a prospective cohort study.
BACKGROUND
Venous thromboembolism (VTE) is a multicausal disease which recurs. Hematocrit is associated with a thrombotic risk. We aimed to investigate if hematocrit is associated with the recurrence risk.


METHODS
Patients with a first VTE were followed after anticoagulation. Patients with VTE provoked by a transient risk factor, natural inhibitor deficiency, lupus anticoagulant, homozygous or double heterozygous defects, cancer, or long-term antithrombotic treatment were excluded. The study endpoint was recurrent VTE.


RESULTS
150 (23%) of 653 patients had recurrence. Only high hematocrit was significantly associated with recurrence risk [hazard ratio (HR) for 1% hematocrit increase with the third tertile 1.08; 95% CI 1.01-1.15]. No or only a weak association for hematocrits within the first and second tertile was seen (HR 1.03; 95% CI 0.97-1.09, and 1.07; 95% CI 1.00-1.13). Hematocrit was associated with recurrence risk only among women. After five years, the probability of recurrence was 9.9% (95% CI 3.7%-15.7%), 15.6% (95% CI 9.7%-21.2%) and 25.5% (95% CI 15.1%-34.6%) in women, and was 29.2% (95% CI 21.1%-36.5%), 30.1% (95% CI 24.1%-35.7%) and 30.8% (95% CI 22.0%-38.7%) in men for hematocrits in the first, second and third tertile, respectively. Men had a higher recurrence risk (1.9; 95% CI 1.1-2.7; p = 0.03), which dropped by 23.5% after adjustment for hematocrit. Hematocrit was not a significant mediator of the sex-difference in recurrence risk (p = 0.223).


CONCLUSIONS
High hematocrit is associated with the recurrence only in women. The different recurrence risk between men and women is possibly partly explained by hematocrit.
Department of Medicine I, Medical University of Vienna, Vienna, Austria.
Lisbeth
L
Eischer
Verena
V
Tscholl
Georg
G
Heinze
Ludwig
L
Traby
Paul A
PA
Kyrle
Sabine
S
Eichinger
D001317:Austria; D015331:Cohort Studies; D023381:Endpoint Determination; D005260:Female; D006400:Hematocrit; D006801:Humans; D008297:Male; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012008:Recurrence; D012307:Risk Factors; D012737:Sex Factors; D018709:Statistics, Nonparametric; D020246:Venous Thrombosis / Q000453:epidemiology* / Q000517:prevention & control*