Activated partial thromboplastin time (APTT) is a commonly used screening test for haemostatic defects in the intrinsic and common pathway of the coagulation cascade, as well as the contact activation system. Thus, FII, FV, FVIII, FIX, FX, FXI, FXII, prekallikrein and high-molecular weight kininogen deficiencies can result in a prolonged APTT.

The MRX APTT reagent utilises colloidal silicate as contact activator to activate the intrinsic pathway of the coagulation cascade. This ensures sensitivity to mild deficiencies of FVIII, FIX, and FXI. MRX APTT is sensitive to heparin, FVIII, FIX and FXI, while being insensitive to the potential interferent lupus anticoagulant. Thus, MRX APTT is suitable for haemophilia screening. MRX APTT reagent contains the contact activator silicate and phospholipids to ensure a highly consistent and stable product.