The objective is to demonstrate the performances of STA® - Apixaban Calibrator & STA® - Apixaban Control used in combination with STA® - Liquid Anti-Xa to measure apixaban concentration in plasma. Anti-Xa results will be compared to LCMS (liquid chromatography - mass spectrometry) for validation of the assay. For this study, the anti-Xa assay will be performed on fresh samples only.

The results will be used to complete results obtained previously on frozen samples.

About 60 samples from patients on apixaban meeting inclusion/exclusion criteria will be included in this study. Two sites will be in charge of sample recruitment and anti-Xa testing. A third site will be in charge of LCMS testing.

Inclusion Criteria:

• Age ≥ 75 years,
• Weight ≤ 60 kg,
• Haematocrit below normal values as determined by local laboratory or < 40% for male and < 37% for female
• Renal impairment documented (creatinine clearance ≤ 80 mL/min as per Cockcroft -Gault equation) or serum creatinine ≥ 1.5 mg/dL
• Co-medication with aspirin or any other NSAIDs (nonsteroidal anti-inflammatory drugs)
• Co-medication with anti-platelet agents

Exclusion Criteria:

• Patients less than 18 years old
• Patients under other anti-coagulant treatment
• Samples that are not collected, stored, or handled in accordance with sample collection procedures defined above.

Patients treated with apixaban presenting at least one of the listed inclusion criteria.