It’s an enzyme which stabilizes the blood clotting system. The main function of Factor XIII or fibrin is to interlink the fibrin which is basic clotting unit. It consists of two subunits Factor XIII A and Factor XIIIB. A is the active portion of this molecule while B has the accessory function. B portion acts as the carrier and inhibits protein degradation within the plasma. Normal standard range of Factor XIIIA and Factor XIII B is 60-130u/DL.