A global assay that measures all procoagulant proteins with the exception of Factor VII. The test is used primarily as a screening tool for deficiencies (some of which may cause bleeding) in the intrinsic pathway of coagulation. Two other uses for the assay are in monitoring unfractionated heparin and in the laboratory detection of the Lupus Anticoagulant. The APTT is the time in seconds required for a fibrin clot to form in a platelet poor plasma sample after an optimal amount of activating agent, phospholipid, and calcium chloride have been added. The slide show entitled Intrinsic Pathway-APTT shows which coagulation factors are tested by the APTT.
