Protein S is an anticoagulant protein and a cofactor of protein C. It is recommended to explore it first by a functional (chronometric) technique by assessing its cofactor activity of activated protein C. Existing tests measure the prolongation of a coagulation time. These tests are all dependent on factor V, but some patients have mutations in factor V (including V Leiden) that make them resistant to activated protein C activity. It is suspected that these mutations lead to underestimations of protein S activity by chronometric technique.

Inclusion criteria:

• Patient of legal age (≥ 18 years)
• Patient for whom a sample has been sent to the HUS Hematology Laboratory for measurement of protein S activity between 28/12/2009 and 29/12/2020
• Patient who does not object to the reuse of his/her medical data for scientific research purposes.

Exclusion criteria:

• Minor patient
• Patient with incomplete data

Adult patients (≥ 18 years) for whom a sample has been sent to the HUS Hematology Laboratory for measurement of protein S activity between 28/12/2009 and 29/12/2020