Partial thromboplastin time
partial thromboplastin time (PTT) or activated partial thromboplastin time (aPTT or APTT) is a performance indicator measuring the efficacy of both the “intrinsic” (now referred to as the contact activation pathway) and the common coagulation pathways. Apart from detecting abnormalities in blood clotting, it is also used to monitor the treatment effects with heparin, a major anticoagulant. It is used in conjunction with the prothrombin time (PT) which measures the extrinsic pathway. Kaolin cephalin clotting time (KccT) is a historic name for the activated partial thromboplastin time.Blood samples are collected in tubes with oxalate or citrate to arrest coagulation by binding calcium. The specimen is then delivered to the laboratory. In order to activate the intrinsic pathway, phospholipid, an activator (such as silica, celite, kaolin, ellagic acid), and calcium (to reverse the anticoagulant effect of the oxalate) are mixed into the plasma sample. The time is measured until a thrombus (clot) forms. This testing is performed by a medical technologist. Shortening of the PTT is considered to have little clinical relevance, but some research indicates that it might increase risk of thromboembolism. Normal PTT times require the presence of the following coagulation factors: I, II, V, VIII, IX, X, XI, XII. Notably, deficiencies in factors VII or XIII will not be detected with the PTT test. APTT may indicate:
Sepsis coagulation factor consumption
Presence of antibodies against coagulation factors (factor inhibitors)
To distinguish the above causes, mixing tests are performed, in which the patient’s plasma is mixed (initially at a 50:50 dilution) christian louboutin outlet with normal plasma. If the abnormality does not disappear, the sample is said to contain an “inhibitor” (either heparin, antiphospholipid antibodies or coagulation fac christian louboutin outlet tor specific inhibitors), while if it does correct a factor deficiency is more likely. Deficiencies of factors VIII, IX, XI and XII and rarely von Willebrand factor (if causing a low factor VIII level) may lead to a prolonged aPTT corre christian louboutin outlet cting on mixing studies.
Laboratory findings in various platelet and coagulation disorders (V T)Vitamin K deficiency or warfarinNor christian louboutin outlet mal or mildly prolonged.