A client is receiving a continuous intravenous infusion of heparin sodium to treat deep vein thrombosis. The client’s activated partial thromboplastin time is 77 seconds. Based on this result, nurse anticipated which of following prescriptions?

Correct Answer: A. Maintain the rate of the heparin infusion.

The normal activated partial thromboplastin time is between 20 to 36 seconds. In the treatment of deep vein thrombosis, the therapeutic range is to maintain the aPTT level between 1.5 and 2.5 times the normal. This means that the client’s aPTT level should not be less than 30 seconds or greater than 90 seconds. Thus the client’s aPTT of 77 seconds is within the normal therapeutic range, and the dose/rate should not be changed.

• Option B: Therapeutic monitoring for heparin includes activated partial thromboplastin time (aPTT) and activated clotting time (ACT). Both of these are aspects of clotting time, which are prolonged by therapeutic heparin doses. Activated partial thromboplastin time is performed at baseline and every 6 hours until 2 or more therapeutic values are obtained, then aPTT can be assessed every 24 hours.
• Option C: Dose titrations are made based on the results of the aPTT. Hospitals have dosing nomograms specific to their target aPTT, which may vary depending upon the laboratory reagent used for their test. Therapeutic aPTT is considered therapeutic at 1.5 to 2 times control, which also varies from facility to facility based on controls.
• Option D: ACT is less sensitive than aPTT. ACT will only detect abnormalities when there is 95% abnormality rate in the factors, whereas aPTT can detect when there is 70% abnormality. ACT may also be affected when platelets are abnormal, which can result from the administration of heparin.