What is the therapeutic range for aPTT?

• A. 46-70 seconds
• B. 30-50 seconds
• C. 60-90 seconds
• D. 20-40 seconds

Answer: (A)

Monitoring unfractionated heparin therapy relies on the aPTT to gauge how long the blood takes to clot. aPTT measures the intrinsic and common pathways of coagulation and is prolonged by heparin. The goal is to keep the aPTT in a therapeutic range that corresponds to about 1.5–2.5 times the patient’s normal (control) value. In many labs, this falls around 46–70 seconds, which is why that range is considered the therapeutic window for heparin anticoagulation. If the aPTT is below this range, the dose of heparin is increased; if it’s above, the dose is reduced or held and the test is repeated. Regular monitoring (often every 4–6 hours after dose changes) ensures the patient stays within a safe range.