PTT
Activated Partial Thromboplastin Time (aPTT/PTT) measures how long it takes blood to clot through the intrinsic pathway. It is used to evaluate clotting disorders and monitor heparin therapy.
Category: Coagulation
Also known as: ptt, aptt, partial thromboplastin time, activated partial thromboplastin time
Reference range: 25–35 seconds (Source: ABIM)
Standard unit: seconds
High values may indicate
Prolonged aPTT may indicate clotting factor deficiencies (such as hemophilia), heparin therapy, von Willebrand disease, lupus anticoagulant, or liver disease.
Low values may indicate
Shortened aPTT is uncommon but may indicate a hypercoagulable state or elevated factor VIII levels related to acute inflammation.
Frequently asked questions
- What is a normal PTT level?
- A typical reference range for PTT is 25–35 seconds (source: ABIM). Reference ranges vary by laboratory, age, and sex, so always compare against the range on your own lab report.
- What units is PTT measured in?
- PTT is most commonly reported in seconds. Labs in different countries may use other units — you can convert between them with BloodId's blood test unit converter.
- Where do PTT reference ranges come from?
- BloodId uses ABIM standard reference ranges and educational information from MedlinePlus (see our methodology). Reference ranges still vary by lab, age, and sex, so always compare against your own report.
- Can I track PTT over time?
- Yes. Upload results from any lab and BloodId charts your PTT over time against its reference range, so you can see whether the trend is rising, falling, or stable.