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A role for transient infections in the aetiology of venous thrombosis (VT) has been suggested. This study aimed to determine whether individuals who receive antibiotic treatment (as a proxy for infections) have an increased risk of first and recurrent VT and whether infections should be seen as a provoking risk factor for VT. We used the self-controlled case series method to study the risk of first VT during antibiotic prescriptions. The risk of recurrent VT during antibiotic use was estimated by of time-dependent Cox-regression. A total of 2547 patients with a first VT were included and followed for a median of 5·9 years for recurrence (1999-2010), in whom 114 first events occurred during antibiotic use. We found a five-fold increased risk of first VT during antibiotic treatment: [incidence-rate-ratio 5·0; 95% confidence interval (CI), 4·0-6·1]. Antibiotic use was associated with a 2·0-fold (95% CI, 1·1-4·0) increased risk of recurrent VT. Patients with an unprovoked first VT who used antibiotics shortly before this event, had a similar risk of recurrence as patients with a provoked first VT (adjusted hazard ratio 1·1; 95% CI, 0·7-1·7). Individuals who receive antibiotics have an increased risk of first and recurrent VT and infections should be considered a provoking risk factor for VT., (© 2017 John Wiley & Sons Ltd.)

We determined in a prospective cohort of patients treated with vitamin K antagonists for venous thrombosis, the course of factor VIII (FVIII:C), C-reactive protein (CRP) and fibrinogen levels, to assess the influence of the acute phase reaction on FVIII:C levels. Second, we hypothesized that patients with preceding infectious symptoms might have higher levels of FVIII:C at baseline than patients without those. We included 75 patients. Blood was sampled at baseline, once during treatment (t=1) and at the end of treatment (t=2). Mean levels of FVIII:C were 207, 186 and 175IU/dL (p for trend 0.003) at baseline, t=1 and t=2 respectively. Eight-eight percent of patients had an elevated FVIII:C at baseline, 75% at t=1 and 72% at t=2 (p for trend 0.045). Mean levels of FVIII:C were not different in patients with or without preceding infectious symptoms (206 versus 205IU/dL respectively). A baseline CRP level below 62mg/L could best distinguish between patients who will keep an elevated FVIII:C and those who will drop below 150IU/dL. We conclude that FVIII:C levels are partially influenced by the acute phase reaction, especially in patients who keep a persistent elevated FVIII:C during treatment. Preceding infectious symptoms did not influence baseline FVIII:C levels., (Copyright © 2011 Elsevier Ltd. All rights reserved.)