Activated partial thromboplastin time APTT

Activated partial thromboplastin time (aPTT) is a coagulation assay, which measures the time for plasma to clot upon activation by a particulate substance (e.g., kaolin) in the presence of negatively charged phospholipids. 

Before administering the first dose of heparin, the nurse obtains the patients vital signs. The most commonly used test to monitor heparin is activated partial thromboplastin time (APTT). Blood is drawn for laboratory studies before giving the first dose of heparin to obtain baseline data (See the discussion on preadministration assessment for the oral anticoagulants.)... 

A number of laboratory tests are available to measure the phases of hemostasis described above. The tests include platelet count, bleeding time, activated partial thromboplastin time (aPTT or PTT), prothrombin time (PT), thrombin time (TT), concentration of fibrinogen, fibrin clot stabifity, and measurement of fibrin degradation products. The platelet count quantitates the number of platelets, and the bleeding time is an overall test of platelet function. aPTT is a measure of the intrinsic pathway and PT of the extrinsic pathway. PT is used to measure the effectiveness of oral anticoagulants such as warfarin, and aPTT is used to monitor heparin therapy. The reader is referred to a textbook of hematology for a discussion of these tests. 

Patient is coagulopathic or has received heparin within past 48 h and has an elevated activated partial thromboplastin time (aPTT)... 

II Umbilical cord, joint, and mucosal tract bleeding Prolonged prothrombin (PT) and activated partial thromboplastin time (aPTT) Specific assay for prothrombin... 

Activated partial thromboplastin time aPTT is performed by adding calcium phospholipids and kaolin to citrated blood and measures the time required for a fibrin clot to form. In this manner, aPTT measures the activity of intrinsic and common pathways. Prolongation of aPTT may be due to a deficiency or inhibitor for factors II, V, VIII, IX, X, XI, and XII. It also may be due to heparin, direct thrombin inhibitors, vitamin K deficiency, liver disease, or lupus anticoagulant. 

The dose is titrated to maintain the activated partial thromboplastin time (aPTT) between 50 and 70 seconds. The first aPTT should be measured at... 

The activated partial thromboplastin time (aPTT) should be measured prior to initiation of therapy then no sooner than 6 hours after beginning the infusion or after a dose change. The traditional therapeutic range is 1.5 to 2.5... 

Pharmacology Enoxaparin, tinzaparin, and dalteparin are LMWHs. These agents enhance the inhibition of Factor Xa and thrombin by binding to and accelerating antithrombin activity. They preferentially potentiate the inhibition of Factor Xa, while only slightly affecting thrombin and clotting time (activated partial thromboplastin time [APTT] or PT). 

Determine patient baseline activated partial thromboplastin time (aPTT) prior to initiation of therapy with lepirudin, because lepirudin should not be started in patients presenting with a baseline aPTT ratio of 2.5 or more in order to avoid initial overdosing. 

Initial dosage in HIT or heparin-induced thrombocytopenia and thrombosis syndrome (HITTS) Before administering argatroban, discontinue heparin therapy and obtain a baseline activated partial thromboplastin time (aPTT). The recommended initial dose of argatroban for adults without hepatic impairment is 2 mcg/kg/min administered as a continuous infusion (see table). 

Therapy with heparin occurs in an inpatient setting. Heparin inhibits both in vitro and in vivo clotting of blood. Whole blood clotting time and activated partial thromboplastin time (aPTT) are prolonged in proportion to blood heparin concentrations. 

Activated partial thromboplastin time (aPTT) or protamine activated clotting time (ACT) 15 min after dose, then in several hr... 

Activated clotting time (ACT) and activated partial thromboplastin time (aPTT) are relatively unaffected by LMWH. Anti-Xa activity can be used to monitor anticoagulation activity, but this is expensive and time-consuming and is seldom indicated. Although protamine has some effect on LMWH, about 60-80% of the antithrombotic activity will persist. This is because of the reduced protamine binding to these drugs and because only the anti-IIa activity is completely reversed whereas anti-Xa activity is only partially neutralised. 

The indications for the use of heparin are described in the section on clinical pharmacology. A plasma concentration of heparin of 0.2-0.4 unit/mL (by protamine titration) or 0.3-0.7 unit/mL (anti-Xa units) usually prevents pulmonary emboli in patients with established venous thrombosis. This concentration of heparin will prolong the activated partial thromboplastin time (aPTT) to 2-2.5 times that of the control value. This degree of anticoagulant effect should be maintained throughout the course of continuous intravenous heparin therapy. When intermittent heparin administration is used, the aPTT should be measured 6 hours after the administered dose to maintain prolongation of the aPTT to 2-2.5 times that of the control value. 

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