The APT is one of the most valuable screening tests that is sensitive to: deficiency of all blood coagulation factors (except factor VII) of heparin, specific (antibodies to factors VIII and IX) and nonspecific coagulation inhibitors (systemic lupus erythematosus). The main function of the APTT is to screen for disorders of the intrinsic coagulation pathway. It should be borne in mind that the prolongation of the APTT occurs with a 30-40% decrease in the level of any of the coagulation factors. Shortening of the PTT indicates an increase in coagulation (hypercoagulability).