Associations Between Free Protein S and Factor VIII Levels with Traditional Arterial Thrombotic Risk Factors and Their Risk On Arterial Thrombosis. Results From a Retrospective Family Cohort Study.
Authors: Mulder René , van Schouwenburg Inge M , Mahmoodi Bakhtawar Khan , Veeger Nic J.G.M. , Mulder André B , Middeldorp Saskia , Kluin-Nelemans Hanneke C. , Lijfering Willem M 
Published: October 2019

Abstract
Abstract 25

Introduction:
Accumulating evidence shows that venous and arterial thrombosis may be viewed as two diseases with similar pathophysiological entities. Both high factor VIII and low free protein S levels are risk factors for venous thrombosis, but if, and in what way, these thrombophilic factors also increase the risk of arterial thrombosis is unknown.

Patients and Methods:
In a single-center retrospective cohort study of families with thrombophilia, we performed a post-hoc analysis to identify if relatives with high factor VIII or low free protein S levels were at risk of arterial thrombosis. Clinical data were collected before laboratory testing. To avoid bias, all probands were excluded from the analyses. In addition, relatives with protein S deficiency type I were excluded from analysis when analyzing effects of free protein S. Factor VIII:C levels were measured by one-stage clotting assays and were considered increased at levels above 150 IU/dL. Free protein S antigen levels were measured by enzyme-linked immunosorbent assay after precipitation of protein S complexed with C4b-binding protein with polyethylene glycol. Free protein S antigen levels were considered decreased at levels below the normal range (< 65 IU/dL). Coronary and peripheral arterial disease had to be symptomatic and angiographically proven, whereas myocardial infarction was diagnosed according to clinical, enzymatic and electrocardiographic criteria. Known risk factors for arterial thrombosis were recorded and included: hypertension, hyperlipidemia, the presence of diabetes mellitus, smoking habits or obesity. Absolute risks of first arterial thrombosis in relatives with high factor VIII or low free protein S levels were calculated. Linear regression was used to determine the relation between factor VIII levels and free protein S levels, respectively, combined with traditional arterial thrombotic risk factors. Adjustments were made for age and sex. Cumulative distribution functions were constructed to visualize a possible relationship between factor VIII and free protein S levels, respectively, and BMI

Results:
Of 1468 relatives tested for thrombophilia, 1399 were analyzed on factor VIII and 1143 on free protein S. Forty-six percent were male. Mean age at enrollment was 45 years. Mean factor VIII level was 146 IU/dL and mean free protein S level 80 IU/dL. High factor VIII levels were observed in 39% of relatives and low free protein S levels in 23% of relatives. First arterial thrombotic events were documented in 86 relatives at a mean age of 57 years. Annual incidence of arterial thrombosis in relatives with high factor VIII levels was 0.29% (95%CI, 0.22-0.38) compared to 0.13% (95%CI, 0.09-0.19) in relatives with normal factor VIII levels. In relatives with low free protein S levels, this risk was 0.26% (95%CI, 0.16-0.40), compared to 0.14% (95%CI, 0.10-0.20) in relatives with normal free protein S levels. Relatives with hypertension, diabetes mellitus, and obesity had mean factor VIII levels (age and sex adjusted) that were 11 IU/dL, 18 IU/dL, and 21 IU/dL higher than relatives without these arterial thrombotic risk factors, which were statitically significant findings. In addition, a dose response relation could be demonstrated between increasing factor VIII and body mass index (Figure). None of these associations were shown for free protein S.

Conclusions:
Both high factor VIII and low free protein S levels were a risk factor for arterial thrombosis in thrombophilic families. High factor VIII levels were particularly observed in relatives with traditional arterial thrombotic risk factors, suggesting that increase of these levels were acquired. Free protein S levels were not influenced by these arterial thrombotic risk factors which assumes that low free protein S levels were genetically determined.

Disclosures:
No relevant conflicts of interest to declare.