Weekly Monitoring Strategy of Capillary INR Versus Monthly Monitoring Strategy of Venous INR in Elderly Patients in a Nursing Home.

This primary care study aims to compare the "time in therapeutic range" (TTR) of two strategies for monitoring the international normalized ratio (INR) over 6 months in nursing homes. The population consists of frail elderly patients for whom Anti-Vitamin K treatments are frequent, and who are consequently more prone to embolic and hemorrhagic complications.

Biological monitoring is essential to avoid strokes, deep vein thrombosis and hemorrhage. Generally speaking, this consists of a venous sampling for the international normalized ratio (INR), for which the therapeutic target is approximately 2.5 (tolerance range between 2 and 3) for atrial fibrillation (AF) and deep vein thrombosis (DVT). INR values below 2 indicate high risks of a stroke or DVT, whereas INR values over 3 refer to high risks of hemorrhage. INR monitoring requires monthly follow-ups or even more frequently if the HAS BLED score is ≥ 3.

One parameter used to evaluate the benefit/risk ratio is the "time in therapeutic range" (TTR), referring to the time spent within the INR therapeutic target (INR between 2 and 3 for patients with Atrial Fibrillation/ Deep Vein Thrombosis). It is calculated using the Rosendaal method. According to the "European Society of Cardiology" guidelines, the minimum threshold necessary for a good risk/benefit ratio is 70%. In other countries, it has been shown that the TTR is higher: 61% in Canada, 64.4% in Spain, 68.9% in Italy and 76.2% in Sweden. Moreover, TTR determines the benefit/risk ratio of the treatment, which means that patients with a TTR \< 60% have more than 2% absolute total mortality per patient-year compared to patients with TTR \> 60%.

As for the pilot study (Manuscript accepted in August 2019 in the Journal of Internal Medicine ), we expect approximately half the patients to be aged over 90. Patients will be recruited in nursing homes where they are monitored by nurses and care quality managers who are responsible for ensuring compliance with good clinical practices. This limits the risk of non-compliance with preanalytical venous INR conditions. Eighteen percent of subjects over 85 are treated with vitamin-K antagonists (VKA). For elderly patients with atrial fibrillation (AF) or deep venous thrombosis (DVT), stroke prophylaxis is a real clinical challenge. VKA treatments are indicated for the prevention of strokes in patients with Atrial Fibrillation, DVT or those who have received heart valve implants. VKAs have a narrow therapeutic range: if they are under-dosed, the risk of embolism (AVC and DVT) is high, whereas in the event of an overdose, the risk of bleeding is high. Given the annual incidence of severe hemorrhage (3-5%), the risk of a hemorrhage is their main side effect. The incidence of brain hemorrhages is 0.6 per 100 patient-years, for gastrointestinal bleeding it is 1.0 per 100 patient-years, and the risk of other serious bleeding is 1.4 per 100 patient-years. This risk of bleeding is usually assessed using the HAS-BLED score. The risk of hemorrhage is 4.2% per year in patients over 75 versus 1.7% per year for those under 75.

Following the results of a pilot study (manuscript accepted in the Journal of Internal Medecine), the hypothesis is that a weekly monitoring strategy for capillary INR should increase the TTR of nursing home patients by 12% compared to the usual monitoring by venous INR, resulting in a decrease of thrombotic or hemorrhagic events.

Eligibility Criteria:
Inclusion Criteria: The population corresponds to nursing homes patients treated with Vitamin K Antagonists for more than six months, because INRc cannot be used while anticoagulation treatment is being introduced.

* The patient or his/her trusted-person/legal representative/tutor signed the consent form
* The patient is an adult and lives in a nursing home
* The patient has been on treatment with Vitamin K Antagonists for more than six months
* The patient's target INR range is 2,5 \[2-3\] or 3 \[2,5-3,5\]
* The patient is affiliated to a health insurance program

Exclusion Criteria:

* The patient is participating in a Type 1 interventional study involving human beings (Jardé law).
* The patient is in an exclusion period determined by another study
* The patient is under safeguard of justice.
* It is not possible to give the patient (or his/her trusted-person/legal representative/tutor) informed information.
* The patient has a short life expectancy (\< 1 month)
* The Karnofky index is ≤ 20%