In shortLupus anticoagulant is an antibody detected through phospholipid-dependent clotting tests. Despite the name, its clinical meaning is an increased risk of thrombosis and pregnancy complications — not bleeding. A positive result is confirmed with a repeat test at least 12 weeks later.
Reference ranges
| Group | Reference range |
|---|---|
| Result — typical range (international reference, not a national standard) | negative / positive (reported against the laboratory's cutoff) |
Lab Tests Online describes a qualitative result. Persistence — a positive test repeated after 12 or more weeks — is what carries diagnostic weight.
What this marker is
The antibody binds phospholipids used in clotting tests, so clotting times look prolonged in the laboratory. In the body, however, the same antibody promotes clot formation — it is a marker of antiphospholipid syndrome.
Testing is ordered after unexplained venous or arterial clots, recurrent pregnancy loss, or an unexpectedly prolonged aPTT that does not correct in mixing studies.
When it is high
Persistent positivityTwo positive tests at least 12 weeks apart, together with a clot or pregnancy complication, meet the criteria for antiphospholipid syndrome.
Transient positivityInfections and some medicines can cause a temporary positive result that disappears on retesting.
When it is low
NegativeNo evidence of the antibody; a negative result does not rule out other causes of clotting.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Anticoagulant therapy (interferes with the assays)Acute infectionSample handling
How to prepare
Blood from a vein. Ideally the test is not performed during an acute clot or while on anticoagulants, because both distort the assays — the provider chooses the timing.
When a retest makes sense
A positive result is always confirmed with a repeat test at least 12 weeks later before any long-term conclusions.
Who usually reviews this result
A result outside the reference range is usually reviewed by: your GP or primary care doctor; a hematologist or rheumatologist for antiphospholipid syndrome. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names:
Lupus anticoagulantLALupus inhibitor
Lupus anticoagulantLALupus inhibitor
Units
Measured in: qualitative result
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
Frequently asked questions
Does lupus anticoagulant mean lupus?
No. The name is historical — most people with a positive result do not have systemic lupus erythematosus.
Why repeat after 12 weeks?
Many positives are temporary (after infections or clots). Only persistent positivity defines antiphospholipid syndrome.
Can I be tested while on blood thinners?
Anticoagulants interfere with the assays; when possible, testing is scheduled before starting or during a controlled pause decided by the provider.
Sources
- Lupus anticoagulant testing: Lab Tests Online — Testing.com (AACC). Accessed: August 31, 2026.