Which is the normal range for aPTT?

Which is the normal range for aPTT?

• A. 30-40 seconds (heparin)
• B. 15-25 seconds
• C. 60-70 seconds
• D. 20-30 seconds

Answer: (A)

Activated partial thromboplastin time (aPTT) reflects how long the intrinsic and common coagulation pathways take to form a clot. The normal value is not fixed across all labs because reference ranges vary by the reagents used, but a common teaching range is about 30 to 40 seconds. This serves as the baseline when a patient is not on anticoagulants. When unfractionated heparin is given, the goal is to prolong the aPTT to indicate therapeutic anticoagulation, typically about 1.5 to 2.5 times the normal value, which usually falls around 60 to 80 seconds depending on the assay. So for a question asking the normal range, 30–40 seconds is the best-fitting choice. The other ranges correspond to either too short a time or a therapeutic range for patients on heparin, not the normal baseline. Always check the specific lab's reference range.

Activated partial thromboplastin time (aPTT) reflects how long the intrinsic and common coagulation pathways take to form a clot. The normal value is not fixed across all labs because reference ranges vary by the reagents used, but a common teaching range is about 30 to 40 seconds. This serves as the baseline when a patient is not on anticoagulants.

When unfractionated heparin is given, the goal is to prolong the aPTT to indicate therapeutic anticoagulation, typically about 1.5 to 2.5 times the normal value, which usually falls around 60 to 80 seconds depending on the assay. So for a question asking the normal range, 30–40 seconds is the best-fitting choice. The other ranges correspond to either too short a time or a therapeutic range for patients on heparin, not the normal baseline. Always check the specific lab's reference range.