Activated protein C resistance test

[5][9] The initiation phase accounts for less than 5% of total thrombin generation, making aPTT-based tests poorly indicative of hypercoagulability in general.

[10][11] The aPTT-based assay is more sensitive to levels of prothrombin and factor VIII, whereas the ETP-based test is more sensitive to levels of tissue factor pathway inhibitor (TFPI) and protein S.[5] The ETP-based test has traditionally been performed using methods such as the calibrated automated thrombogram (CAT) and has been limitedly available due to its technical difficulty.

[13][14][5][4][2][15] Pregnancy[7] and ethinylestradiol (EE)-containing combined birth control pills increase APC resistance as measured by either the aPTT- or ETP-based test.

[14] Increased APC resistance with both the aPTT-based and ETP-based tests has been observed with feminizing hormone therapy in transgender women, which involves higher doses of estradiol than are used in other contexts.

[21] By 2020 however, a validated methodology was developed aiming to propose a standardized and harmonized scale for ETP-based APC resistance, the normalized activated protein C sensitivity ratio (nAPCsr).

Thrombin generation curves in the absence (HPP -APC) and presence (HPP +APC) of activated protein C (APC) in healthy pooled plasma and in plasma of women on various combined oral contraceptives . [ 5 ] The contraceptives are estetrol/drospirenone (E4/DRSP), ethinylestradiol/levonorgestrel (EE/LNG), ethinylestradiol/desogestrel (EE/DSG), and ethinylestradiol/drospirenone (EE/DRSP). [ 5 ]