Prothrombin fragment 1+2Prothrombin fragment 1+2 (F1+2), also written as prothrombin fragment 1.2 (F1.2), is a polypeptide fragment of prothrombin (factor II) generated by the in vivo cleavage of prothrombin into thrombin (factor IIa) by the enzyme prothrombinase (a complex of factor Xa and factor Va).[1][2][3] It is released from the N-terminus of prothrombin.[3] F1+2 is a marker of thrombin generation and hence of coagulation activation.[4][3][1] It is considered the best marker of in vivo thrombin generation.[1] F1+2 levels can be quantified with blood tests and is used in the diagnosis of hyper- and hypocoagulable states and in the monitoring of anticoagulant therapy.[4][1] It was initially determined with a radioimmunoassay, but is now measured with several enzyme-linked immunosorbent assays.[1] The molecular weight of F1+2 is around 41 to 43 kDa.[4][1] Its biological half-life is 90 minutes and it persists in blood for a few hours after formation.[4][3][1] The half-life of F1+2 is relatively long, which makes it more reliable for measuring ongoing coagulation than other markers like thrombin–antithrombin complexes and fibrinopeptide A.[1][3] Concentrations of F1+2 in healthy individuals range from 0.44 to 1.11 nM.[4] F1+2 levels increase with age.[3] Levels of F1+2 have been reported to be elevated in venous thromboembolism, protein C deficiency, protein S deficiency, atrial fibrillation, unstable angina, acute myocardial infarction, acute stroke, atherosclerosis, peripheral arterial disease, and in smokers.[3][1] Anticoagulants have been found to reduce F1+2 levels.[1] F1+2 levels are increased with pregnancy[5] and by ethinylestradiol-containing birth control pills.[6] Conversely, they do not appear to be increased with estetrol- or estradiol-containing birth control pills.[6] However, F1+2 levels have been reported to be increased with oral estrogen-based menopausal hormone therapy, whereas transdermal estradiol-based menpausal hormone therapy appears to result in less or no consistent increase.[7] References
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