When monitoring heparin therapy, the activated partial thromboplastin time (aPTT) should be how many times the control value?

• A. 0.5-1.0 times
• B. 1.0-1.5 times
• C. 1.5-2.0 times
• D. 2.5-3.0 times

Answer: (C)

When using heparin, the goal is to achieve enough anticoagulation without causing bleeding, and the aPTT is the test of choice to gauge that effect. Heparin slows clot formation by enhancing antithrombin, so we compare the patient’s clotting time to their own normal (control) value. The therapeutic target is about 1.5 to 2.0 times the control. For example, if the normal aPTT is 30 seconds, the therapeutic range would be roughly 45 to 60 seconds. Values below this range mean under-anticoagulation; values above it indicate excessive anticoagulation and a higher bleeding risk. The other ranges are either too low to provide adequate anticoagulation or too high, increasing bleeding risk.