The activated partial thromboplastin time (aPTT) is a screening procedure for deficiencies in coagulation factors of the intrinsic coagulation pathway, factors VIII, IX, XI, XII, Fletcher factor and Fitzgerald factor. Severe deficiencies of fibrinogen and factors II, V and X can also be detected by the aPTT. It is a useful and effective method for screening patients with a bleeding tendency, for evaluating the effect of therapy in procoagulant disorders and as the basis for several specific coagulation factor assay procedures. The aPTT is widely advocated as a test for monitoring and regulating heparin therapy. The presence of non-specific inhibitors, such as the lupus anticoagulant, may prolong the aPTT.
The 9:1 blood/citrate ratio must be kept constant. Adjustments for the amount of anticoagulant should be made when the hematocrit is abnormal (above 55%). Mix immediately to prevent clotting.
Collection Instructions
Send whole blood sample(s) at room temperature as soon as possible.
If specimens cannot be shipped immediately, centrifuge and separate plasma within 1 hour of collection, send frozen plasma on dry ice