The goal of this observational study is to learn if certain factors in a person's blood are linked to a history of venous thromboembolic disease (VTED), which includes conditions like deep vein thrombosis.

Lewis system antigens are natural markers found on red blood cells. Past research suggests that people without these specific markers might have a higher chance of developing heart disease, but the link to blood clots in veins is not well understood.

This study aims to answer:

• Are certain Lewis antigen types more common in people with a history of VTE?
• Do the Lewis antigen results relate to other known blood clot risk factors? Researchers will identify Lewis a and b antigens in 100 participants who attend the Haemostasis Disorders Clinic at the University Hospital of Larissa. All participants are people with a personal history of deep vein thrombosis, with or without an inherited or acquired tendency for blood clots.

Researchers will also record other known risk factors for VTED for each participant. This study is self-funded.

Background Since 1992, research has reported a correlation between Lewis antigens and cardiovascular disease, primarily linked to increased endothelial activation in individuals who are Lewis a(-) b(-). Experimental studies in mice suggest an association between the FUT4 and FUT7 genes and the occurrence of venous thromboembolic disease (VTED), but there is a lack of in vivo studies on this subject in humans . This study aims to fill this knowledge gap by investigating this relationship in a clinical setting.

Study Objectives The primary objective is to investigate the relationship between Lewis system antigens and a personal history of VTED. The study will also assess the association between specific Lewis antigen phenotypes and other known risk factors for VTED.

Study Design This is an independent and self-funded, single-center, observational study (p. 1). Lewis a and b antigens will be identified serologically in a specific patient population, and these results will be correlated with existing clinical data on thrombophilia and other VTE risk factors Study Population and Setting The study will include 100 participants (goal sample size for 90% statistical power) with a personal history of deep vein thrombosis, regardless of whether they have hereditary or acquired thrombophilia . All participants are monitored at the Haemostasis Disorders Clinic of the Blood Transfusion Service at the University Hospital of Larissa, Greece. Written informed consent is obtained from all participants after they are fully informed about the study.

Methods and Outcome Measures Lewis antigens are identified using commercial reagents and gel cards from Grifols.

Primary Outcome Measure: The prevalence of different Lewis erythrocyte antigen phenotypes in patients with a history of VTED. (Time Frame: At the time of a single blood draw) Secondary Outcome Measure: The correlation between Lewis phenotypes and the presence of other known VTE risk factors or a confirmed diagnosis of thrombophilia. (Time Frame: Assessed using existing medical records at the time of a single blood draw) Statistical Analysis Statistical analysis will be performed using the SPSS software package.

Inclusion Criteria:

• Adult patients aged 18-78 years with a personal history of deep venous thrombosis and/or Pulmonary Embolism.

Exclusion Criteria:1. Current pregnancy or postpartum period 2. Hepatic insufficiency 3. Alcoholic cirrhosis

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Pateints with personal history of VTE

Our study does not plan to share Individual Participant Data (IPD) primarily due to strict limitations in the original informed consent process; participants did not grant permission for their data to be shared externally.