Activated Partial Thromboplastin Time (aPTT) levels: what's normal, high and low
How long it takes blood to clot via the intrinsic pathway. Used to monitor heparin therapy and screen for clotting disorders.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
The short answer
Activated Partial Thromboplastin Time (aPTT) is measured with a standard blood draw; no fasting is needed. A typical reference range is 25.0 – 35.0 seconds. At TestWell it's $26.99 all-in as PT and PTT (Prothrombin & Partial Thromboplastin Time), results in 1–3 business days, drawn at Quest or Labcorp. An out-of-range result is a prompt to look closer, not a diagnosis.
- Units
- seconds / sec
- Sample
- Blood draw
- Fasting
- Not required
- Results
- 1–3 business days
- Price
- $26.99
- Labs
- Quest or Labcorp
Activated Partial Thromboplastin Time (aPTT) Reference Range
These are the typical adult reference ranges used by major US labs. Your report will include the specific range used by the lab that processed your sample.
| Population | Range |
|---|---|
| age 18+ | 25.0 – 35.0 seconds |
Reference ranges are educational. Always interpret your result with the specific range printed on your lab report and discuss anything outside the range with a clinician.
Have a result in hand? analyze it with your AI assistant using these reviewed ranges, or run it through our explainer. Tools: look up another marker's range · convert lab units
What your Activated Partial Thromboplastin Time (aPTT) result may mean
Often reflects heparin therapy, factor deficiencies, or specific clotting inhibitors.
What a high Activated Partial Thromboplastin Time (aPTT) means: causes, symptoms, next steps ↓Educational only — not a diagnosis. Many factors can influence a single result. Discuss anything that concerns you with a healthcare provider.
What does a high Activated Partial Thromboplastin Time (aPTT) mean?
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.
Common causes of a 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)
Ordered from most to least common.
Symptoms that can go with it
- Easy bruising, heavy periods, prolonged bleeding after cuts or dental work
- Often none — lupus anticoagulant causes clots, not bleeding
What 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
Seek care promptly if
- Prolonged aPTT with active bleeding, or a severe headache after a head injury — emergency care
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 only — not a diagnosis. A single result outside the range is a prompt to look closer with a clinician.
How do you get a Activated Partial Thromboplastin Time (aPTT) test?
Order online, a licensed physician reviews the requisition, and you walk into a nearby lab for the draw. Activated Partial Thromboplastin Time (aPTT) is available on its own or inside these panels — panels cost less per marker when you want the fuller picture.
| Option | Includes | Price |
|---|---|---|
| PT and PTT (Prothrombin & Partial Thromboplastin Time) | This marker only | $26.99 |
Quest vs. Labcorp for Activated Partial Thromboplastin Time (aPTT): which lab should you pick?
Both are CLIA-certified national labs and the result is clinically equivalent, so pick whichever location is closer. Your report will print that lab's own reference range, which can differ slightly from the table above.
| Lab | Available | Price |
|---|---|---|
| Quest Diagnostics | Yes | $54.99 |
| Labcorp | Yes | $26.99 |
| BioReference (NY & NJ) | No | — |
Need help choosing a location? Use the lab finder to see draw sites near your ZIP.
Frequently asked
What does a high Activated Partial Thromboplastin Time (aPTT) mean?
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.
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.
Do I need a doctor's order to test my activated partial thromboplastin time (aptt)?
No. TestWell's licensed physician network reviews and approves your order — usually within minutes. You can place an order online without an in-person visit or a referral from your own doctor.
How long does it take to get Activated Partial Thromboplastin Time (aPTT) results?
Most Activated Partial Thromboplastin Time (aPTT) results are available in 1–3 business days after your specimen arrives at the lab. You'll get an email the moment your results are ready, with everything viewable in your TestWell portal.
How much does a Activated Partial Thromboplastin Time (aPTT) test cost?
Our PT and PTT (Prothrombin & Partial Thromboplastin Time) starts at $26.99. That's the all-in price — no copays, no insurance hoops, no surprise bills. HSA and FSA cards are accepted.
Do I need to fast before my Activated Partial Thromboplastin Time (aPTT) test?
Fasting is not required for the Activated Partial Thromboplastin Time (aPTT) test. You can have your blood drawn any time of day.
Which lab will process my Activated Partial Thromboplastin Time (aPTT) test?
Your test will be processed by Quest Diagnostics, Labcorp, or BioReference depending on which is closest to you and which lab carries the test. All three are CLIA-certified and trusted by hospitals nationwide. You'll choose your lab during checkout from 4,000+ locations.
What can throw off a Activated Partial Thromboplastin Time (aPTT) result?
Aspirin and blood thinners can change a Activated Partial Thromboplastin Time (aPTT) result without anything being wrong. Aspirin and blood thinners can interfere with aptt — these tests do not measure DOAC effect; tell the lab and clinician which anticoagulant you take. Each is explained on our physician-reviewed "Before your test" pages; when one applies, remove it and retest.
Ready to test your activated partial thromboplastin time (aptt)?
Order in two minutes, get physician-approved, and visit a lab the same day. Starts at $26.99.