The purpose of this study is to determine whether the international pharmacogenetic algorithm is better than the standard initiation dosing and whether the two algorithms are suitable for Chinese elderly patients.

The study protocol is a multicenter, randomized, patient-blinded and controlled trial, comparing two approaches among 864 enrolled AF(atrial fibrillation) or DVT(deep venous thrombosis) patients for guiding warfarin initial anticoagulation in Chinese elderly patients: the intervention group using the algorithm of International Warfarin Pharmacogenetic Consortium and its dose revision, and the control group using a standard initiation dose (2.25 mg).The study hypothesis is that the intervention group relative to the control group will increase the percentage of time in therapeutic INR (international normalized ratio) range during the first 3 months.This trial is the first prospective large-scale randomized controlled trial for elders in China. It is of great significance for promoting special crowd individualization of anticoagulants at home and abroad.

Inclusion criteria：1) Chinese male or female aged ≥18 years; 2) Requiring at least 12-week warfarin therapy as judged by clinicians; 3) Subjects with DVT/AF and a post-therapy target INR of 1.5-2.5; 4) Capable of providing written informed consent; 5) Capable of maintaining excellent communications with investigators and completing trial in accordance with trial stipulations.

Exclusion criteria：1) Subjects previously taking warfarin; 2) Known genotypes of CYP2C9 or/and VKORC1; 3) Subjects receiving or expecting to receive other therapies or other anticoagulants; 4) Subjects with contraindications for warfarin; 5) Subjects with severe cognitive dysfunctions; 6) Baseline INR ≥1.5; 7) Subjects with drug or alcohol dependence within the last 12 months; 8) Subjects receiving blood transfusion or bone marrow transplantation within the last 2 weeks; 9) Planning to receive invasive examinations (except for standard endoscopy) with a hemorrhagic tendency or undergoing surgery during trial.10) Prior to randomization, subjects receiving any trial drug or device within the last 3 months or planning to receive such an investigational therapy during trial; 11) Subjects with the following diagnoses or conditions: active malignant carcinomas (diagnosed within the last 5 years), but excluding adequately-treated non-melanoma skin cancer or other non-invasive or in situ cancer (e.g. cervical cancer in situ); anti-neoplastic therapy within the last 5 years (medication, radiotherapy or/and surgery); overt active disease or infection; life expectancy <6 months; 12）Other clinical reasons for unsuitable recruitment as judged by clinicians.