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.)... 

Blood coagulation tests are usually ordered before and during heparin tiierapy, and die dose of heparin is adjusted to die test results. Optimal results of therapy are obtained when the APTT is 1.5 to 2.5 times the control value The LMWHs do not require close monitoring of blood coagulation tests. 

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. 

Check aPTT every 6 h until stable then every 12-24 h o Use beyond 48 h is indicated in patients with refractory... 

For patients receiving concomitant fibrinolytic pharmacotherapy, check an aPTT 3 h after heparin initiation... 

Administer heparin without a loading dose when aPTT <2 x control after fibrinolysis... 

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

If aPTT prolonged 2-4 h after the first dose, may administer an additional 0.5 mg/1 mg if required... 

Monitor aPTT 4 h after the start of the continuous infusion... 

Determine baseline international normalized ratio (INR) and aPTT on DTI monotherapy... 

After the desired overlap and target INR has been reached, withhold the DTI and recheck the INR and aPTT in 4—6 h. Prolonged cessation may be required if the patient initially required a low-dose DTI infusion. If the INR is between 2 and 3 and the aPTT is at/near baseline, the DTI can be discontinued. 

Titrated to maintain aPTT between 1.5 and 2.5 times control for NSTE ACS and 1.5-2 times control (approximately 50-70 seconds) in STE ACS... 

The first aPTT should be measured at 4-6 hours for NSTE ACS and STE ACS in patients not treated with thrombolytics... 

Unfractionated heparin Bleeding, heparin-induced thrombocytopenia Clinical signs of bleeding3 baseline CBC and platelet count aPTT every 6 hours until target then every 24 hours daily CBC platelet count every 2 days (minimum, preferably every day)... 

Warfarin Bleeding, skin necrosis Clinical signs of bleeding3 baseline CBC and platelet count CBC and platelet count every 6 months following hospital discharge baseline aPTT and INR daily INR until two consecutive INRs are within the target range then once weekly x 2 weeks, then every month... 

ACE, angiotensin-converting enzyme aPTT, activated partial thromboplastin time ARB, angiotensin receptor blocker BP, blood pressure CBC, complete blood count ECC, electrocardiogram HR, heart rate INR, International Normalized Ratio RR, respiratory rate SCr, serum creatinine, TTP, thrombotic thrombocytopenic purpura. 

Adjust subsequent doses to attain a goal aPTT based on the institution-specific therapeutic range... 

Unfractionated heparin should not be used during thrombolytic therapy. Neither the aPTT nor any other anticoagulation parameter should be monitored during the thrombolytic infusion... 

If aPTT less than 2.5 times the control value, unfractionated heparin infusion should be started and adjusted to maintain aPTT in therapeutic range... 

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