What is the normal aPTT range for a patient on anticoagulation monitoring?

• A. 60-90 seconds
• B. 20-35 seconds
• C. 40-60 seconds
• D. 10-20 seconds

Answer: (B)

Activated partial thromboplastin time (aPTT) is used to monitor unfractionated heparin therapy, and its normal reference range is the baseline time it takes for clot formation via the intrinsic pathway. The typical normal range is about 25-35 seconds, with many labs using roughly 20-35 seconds as a practical reference. This is why that option best reflects the normal, non-anticoagulated value. When on heparin, clinicians aim for a prolonged aPTT, typically around 60-90 seconds (about 1.5-2.5 times the normal), so ranges like 60-90 are therapeutic targets rather than the normal reference. The 40-60 seconds range would indicate some anticoagulation, but it is not the normal baseline, and 10-20 seconds is abnormally short.