Enrolling participants has halted due to lack of investigator.

The study is a national multicenter prospective observational study, including 200 patients. The main purpose of this study is to explore in more detail the influence of genetic variability (CYP enzymes and vitamin K dependent proteins) and dietary vitamin K status on warfarin dosing, clinical effect and adverse events with emphasis on the initial phase of treatment. The hypothesis is that genetic variability concerning CYP enzymes and vitamin K dependent proteins predict dosing and adverse events during warfarin treatment. The main aim is to individualize warfarin therapy and establish a treatment algorithm based on genotype and dietary vitamin K status to make the anticoagulation therapy with warfarin more secure.

Inclusion Criteria:

• Caucasian
• >18 years of age
• included in the study at the onset of warfarin treatment
• target INR (2-3 for atrial fibrillation, vein thrombosis, pulmonary embolism and 2.5-3.5 for prosthetic heart valves)
• standard indications for warfarin treatment

Exclusion Criteria:

• Non-caucasian
• Clinical significant liver affection
• Heart failure, NYHA class III-IV
• Non-compliant - not able to accomplish protocol demands
• Not able to give informed consent
• Long-term antibiotic therapy
• Malabsorption conditions and inflammatory bowel disease

Patients in need of warfarin treatment (standard indications) are included in the study at the onset of warfarin treatment. About 200 patients will be included.