Activated Partial Thromboplastin Time (aPTT) · high result
What does a high Activated Partial Thromboplastin Time (aPTT) mean?
Short answer
A prolonged aPTT means the intrinsic clotting pathway is slow. Common causes are heparin therapy (intended), a lupus anticoagulant (an antibody that paradoxically raises clot risk), factor deficiencies including hemophilia and von Willebrand disease, liver disease, vitamin K deficiency and — very commonly — a sample problem such as an under-filled tube or heparin contamination from an IV line. A mixing study separates deficiency from an inhibitor.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
When does this result need same-day care?
- Prolonged aPTT with active bleeding, or a severe headache after a head injury — emergency care
What is the normal range for Activated Partial Thromboplastin Time (aPTT)?
- age 18+: 25.0 – 35.0 seconds
Often reflects heparin therapy, factor deficiencies, or specific clotting inhibitors.
Full reference table, citations and testing options: Activated Partial Thromboplastin Time (aPTT) biomarker page.
What are the common causes of high Activated Partial Thromboplastin Time (aPTT)?
- Heparin (therapeutic or line contamination), direct thrombin inhibitors
- Lupus anticoagulant / antiphospholipid antibodies
- Von Willebrand disease, hemophilia A or B, factor XI or XII deficiency
- Liver disease, vitamin K deficiency, warfarin (with a prolonged PT)
- Disseminated intravascular coagulation
- Under-filled or hemolyzed sample (false high)
What symptoms go with high Activated Partial Thromboplastin Time (aPTT)?
- Easy bruising, heavy periods, prolonged bleeding after cuts or dental work
- Often none — lupus anticoagulant causes clots, not bleeding
What do clinicians usually check next?
- Repeat with a clean venipuncture; PT/INR, platelets, fibrinogen
- Mixing study, then specific factor assays or lupus anticoagulant testing
- Hematology referral for any confirmed abnormality before surgery or pregnancy
How do you recheck Activated Partial Thromboplastin Time (aPTT)?
Prices are cash-pay; every order adds one $6 lab processing fee. Physician authorization is included; no insurance or referral needed.
| Test or panel | Type | Price | Fasting | Results |
|---|---|---|---|---|
| PT and PTT (Prothrombin & Partial Thromboplastin Time) | Test · 3 biomarkers | $54.99 | No | 1–3 business days |
Common questions
My aPTT is prolonged but I don't bleed — why?
The two most common reasons: a sample artifact, or a lupus anticoagulant, which prolongs the test in the tube but increases clotting in the body. Both are sorted out by a repeat and a mixing study.
Which bleeding disorder does aPTT catch?
Deficiencies in the intrinsic pathway — factors VIII, IX, XI, XII and von Willebrand factor. A normal aPTT does not exclude mild von Willebrand disease, which needs its own tests.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.