Heparin activated partial thromboplastin time

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. 

FIGURE 7.2 LMWH inhibits factor Xa and minimally affects factor Ha thus, activated partial thromboplastin time is not used to measure its anticoagulant activity. (Reprinted from the American Family Physician published by the American Academy of Family Physicians, February 15th, 1999, in an article entitled Low-molecular-weight heparin in outpatient treatment of DVT. )... 

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

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. 

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. 

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. 

Abbreviations aPTT, activated partial thromboplastin time AT, antithrombin HC, heparin cofactor HIT, heparin-induced thrombocytopenia PCI, percutaneous coronary intervention PF, platelet factor UFH, unfractionated heparin. 

Intravenous infusion of heparin 1000 units per hour starting after the second reteplase bolus. Heparin should be administered for at least 24 hours, preferably for 48-72 hours, aiming to keep activated partial thromboplastin time (aPTT) values 1.5-2 times normal. 

Argatroban has been approved in the USA and Canada for the prophylaxis and treatment of thrombosis in patients with heparin-induced thrombocytopenia, and in Japan and Korea for various thrombotic disorders. Its effects can be monitored using the activated partial thromboplastin time for low doses and the activated clotting time for high doses. Its pharmacology, clinical pharmacology, and uses have been reviewed (7-14). 

The effects on activated partial thromboplastin time and the incidence and chnical relevance of antihirudin antibodies in patients treated with lepirudin have been studied using data from two prospective multicenter studies, in which patients with heparin-induced... 

Antithrombin, in presence of low molecular weight heparin, produces anticoagulation by inhibition of factor Xa. Enoxaparin causes less inactivation of thrombin, inhibition of platelets, and bleeding than standard heparin. Does not significantly influence bleeding time, prothrombin time (PT), activated partial thromboplastin time (APTT). 

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