The Biorex Diagnostics APTT reagent is an in vitro diagnostic assay intended for use in determining activated partial thromboplastin time (APTT) and coagulation factor assays that are based on a modified APTT.

The activated partial thromboplastin time (APTT) is used as a general screening test for the detection of coagulation abnormalities in the intrinsic pathway. The APTT is sensitive to deficiencies or abnormalities of factors VIII, IX, XI, XII, X and II, prekallikrein, high molecular weight kininogen (HMWK), and fibrinogen. APTT is also sensitive to inhibitors of blood coagulation such as lupus inhibitor and fibrin/fibrinogen degradation products. The APTT is the most widely used method for monitoring intravenous heparin anticoagulation therapy.