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PubMed This is a summary of 18 peer-reviewed journal articles Updated
Antiphospholipid Syndrome

Diagnosis and Deciphering Your Lab Results

At a Glance

Antiphospholipid syndrome is not confirmed by one positive blood test. Diagnosis requires a qualifying blood clot or pregnancy complication plus persistent lupus anticoagulant, anticardiolipin, or anti-beta-2 glycoprotein I antibodies on tests at least 12 weeks apart.

Getting a diagnosis for Antiphospholipid Syndrome (APS) can feel like a long and repetitive process. Unlike many conditions that can be confirmed with a single blood draw, APS requires a “waiting game” to ensure the results are accurate and not just a temporary reaction by your immune system.

The Three Core Antibodies

To diagnose APS, doctors look for three specific types of antibodies in your blood [1][2]:

  1. Lupus Anticoagulant (LA): Despite its name, this doesn’t mean you have Lupus. It is a functional test that measures how long it takes for your blood to clot in a test tube [3].
  2. Anticardiolipin (aCL): This antibody targets a specific type of fat molecule (phospholipid) found in cell membranes [4].
  3. Anti-B2-Glycoprotein I (anti-β2GPI): This targets the protein that sticks to those phospholipids [4].

The 12-Week Rule

You may wonder why your doctor insists on repeating your blood tests after 12 weeks. This is the persistence requirement.

Many things—like a common cold, a recent infection, or even certain medications—can cause your immune system to produce these antibodies temporarily [5]. These “transient” antibodies usually disappear within a few weeks and do not increase your risk of blood clots. A diagnosis of APS requires that the antibodies stay in your blood for at least 12 weeks, proving they are persistent [6][7]. However, even after 12 weeks, levels can sometimes fluctuate. It is also important to note that a positive lab test alone does not establish APS without a qualifying clinical event (like a blood clot or specific pregnancy morbidity).

Understanding “Positivity” and Risk

Not all positive results carry the same level of risk. Doctors categorize results based on how many types of antibodies are present [8]:

  • Single Positive: Only one of the three antibodies is present. This is generally lower risk, but a persistently positive Lupus Anticoagulant on its own can still be high risk [9].
  • Double Positive: Two of the three antibodies are present.
  • Triple Positive: All three antibodies—LA, aCL, and anti-β2GPI—are present. This “triple positivity” is associated with the highest risk for both blood clots and pregnancy complications [10][11].

How Blood Thinners Can “Cheat” the Test

If you are already taking blood thinners (anticoagulants) like Warfarin, Heparin, or newer drugs called DOACs (such as Eliquis or Xarelto), they can severely interfere with the Lupus Anticoagulant test [12].

Because the LA test measures clotting time, the presence of a blood thinner can make the test look positive even when it isn’t (a “false positive”) or, occasionally, hide a real positive result [13][14]. WARNING: You must NEVER hold or stop your anticoagulant solely for testing. Instead, your doctor and the laboratory will coordinate using appropriately timed samples, validated mitigation methods, or specialist interpretation [15].

Your Lab Report Checklist

When you receive your lab results, look for these key details to ensure the report is complete:

  • [ ] Antibody Type: Does it list all three (LA, aCL, and anti-β2GPI)?
  • [ ] Isotype: Does it specify IgG or IgM? (IgG is often considered more clinically significant) [16].
  • [ ] Titer/Value: Is the actual number or percentile listed? (For aCL and anti-β2GPI, results are often compared to the lab’s 99th percentile) [4].
  • [ ] Test Method: Was the aCL or anti-β2GPI measured using an ELISA or other validated method? [16].
  • [ ] Reference Range: Does the report show what the lab considers “normal” or “negative”?

New Standards for Diagnosis

In 2023, new international guidelines (the ACR/EULAR criteria) were introduced. These use a point-based system to help classify patients for research studies [16]. While your doctor may use these as a guide, they are very strict research criteria rather than new clinical diagnosis guidelines. You might still have clinical APS even if you don’t “score” enough points for a research classification [17][18]. Your doctor’s clinical judgment, combined with your 12-week confirmation, remains the most important factor in your diagnosis.

Common questions in this guide

Which antibody tests are used to check for antiphospholipid syndrome?
Doctors commonly evaluate lupus anticoagulant, anticardiolipin antibodies, and anti-beta-2 glycoprotein I antibodies. The results are interpreted with your medical history because a positive antibody test alone does not establish antiphospholipid syndrome.
Why do I need another APS blood test after 12 weeks?
Infections and some medicines can cause antiphospholipid antibodies to appear temporarily. Repeating the test at least 12 weeks later helps show whether the antibodies are persistent; diagnosis also requires a qualifying blood clot or pregnancy-related clinical event.
What does triple-positive antiphospholipid syndrome mean?
Triple positivity means lupus anticoagulant, anticardiolipin, and anti-beta-2 glycoprotein I antibodies are all detected. When this pattern persists, it is associated with the highest risk of blood clots and pregnancy complications, although a persistently positive lupus anticoagulant alone can also be high risk.
Can blood thinners change a lupus anticoagulant test?
Yes. Warfarin, heparin, and direct oral anticoagulants can interfere with the clotting-based lupus anticoagulant test and may cause a misleading positive or negative result. Never stop an anticoagulant on your own; your clinician and laboratory should plan the safest testing approach.
What should I check on my antiphospholipid antibody lab report?
Look for the antibody type, IgG or IgM isotype, measured value or titer, test method, and reference range. Comparing results from the same laboratory can make changes easier to interpret, but your clinician should explain what your results mean.
Do the 2023 ACR/EULAR criteria confirm my APS diagnosis?
The 2023 ACR/EULAR criteria are point-based classification criteria designed mainly for research. They can help organize clinical information, but a clinician may diagnose APS using your history, qualifying event, and persistent antibody results even if you do not meet the research score.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Did my test results show 'triple positivity' (all three antibodies present), and how does that change my risk level?
  2. 2.Was my blood sample for the Lupus Anticoagulant test taken while I was on a blood thinner? If so, should we repeat it?
  3. 3.Can we review the specific 'isotype' (IgG vs. IgM) and the 'titer' (the actual number) of my results together?
  4. 4.Now that we have the first positive result, what is the exact date I should come back for my 12-week confirmation test?
  5. 5.Based on the 2023 criteria, do I have enough 'clinical points' from my medical history to meet the classification for APS?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (18)
  1. 1

    Cardiac Manifestations of Antiphospholipid Syndrome: Clinical Presentation, Role of Cardiac Imaging, and Treatment Strategies.

    Tufano A, Di Minno MND, Guida A, et al.

    Seminars in thrombosis and hemostasis 2019; (45(5)):468-477 doi:10.1055/s-0039-1692702.

    PMID: 31216589
  2. 2

    [Laboratory diagnosis of antiphospholipid syndrome: From criteria to practice].

    Joste V, Dragon-Durey MA, Darnige L

    La Revue de medecine interne 2018; (39(1)):34-41 doi:10.1016/j.revmed.2017.02.006.

    PMID: 28302338
  3. 3

    Guidance from the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the International Society on Thrombosis and Haemostasis: Update of the guidelines for lupus anticoagulant detection and interpretation.

    Devreese KMJ, de Groot PG, de Laat B, et al.

    Journal of thrombosis and haemostasis : JTH 2020; (18(11)):2828-2839 doi:10.1111/jth.15047.

    PMID: 33462974
  4. 4

    An update on laboratory detection and interpretation of antiphospholipid antibodies for diagnosis of antiphospholipid syndrome: guidance from the ISTH-SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies.

    Devreese KMJ, Bertolaccini ML, Branch DW, et al.

    Journal of thrombosis and haemostasis : JTH 2025; (23(2)):731-744 doi:10.1016/j.jtha.2024.10.022.

    PMID: 39510414
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    Differences in Antiphospholipid Antibody Profile between Patients with Obstetric and Thrombotic Antiphospholipid Syndrome.

    Anunciación-Llunell A, Muñoz C, Roggenbuck D, et al.

    International journal of molecular sciences 2022; (23(21)) doi:10.3390/ijms232112819.

    PMID: 36361608
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    Persistence of antiphospholipid antibodies over time and its association with recurrence of clinical manifestations: A longitudinal study from a single centre.

    Barilaro G, Coloma-Bazan E, Chacur A, et al.

    Autoimmunity reviews 2022; (21(12)):103208 doi:10.1016/j.autrev.2022.103208.

    PMID: 36202304
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    Laboratory assessment of antiphospholipid syndrome: Laboratory data.

    Kobylecki CJ, Vedel-Krogh S, Afzal S, Goetze JP

    International journal of laboratory hematology 2024; (46(4)):714-721 doi:10.1111/ijlh.14273.

    PMID: 38563299
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    Recent advances in understanding antiphospholipid syndrome.

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    PMID: 28105326
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    IgG phosphatidylserine/prothrombin antibodies as a risk factor of thrombosis in antiphospholipid antibody carriers.

    Tonello M, Mattia E, Favaro M, et al.

    Thrombosis research 2019; (177()):157-160 doi:10.1016/j.thromres.2019.03.006.

    PMID: 30903876
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    Assessment of triple antiphospholipid antibody-positive patients based on clinical and laboratory domains of 2023 ACR/EULAR antiphospholipid syndrome classification criteria.

    Cobanoglu RK, Vega J, Burgos C, Erkan D

    Seminars in arthritis and rheumatism 2025; (74()):152768 doi:10.1016/j.semarthrit.2025.152768.

    PMID: 40578130
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    Antiphospholipid antibody profile based obstetric outcomes of primary antiphospholipid syndrome: the PREGNANTS study.

    Saccone G, Berghella V, Maruotti GM, et al.

    American journal of obstetrics and gynecology 2017; (216(5)):525.e1-525.e12 doi:10.1016/j.ajog.2017.01.026.

    PMID: 28153662
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    Lupus anticoagulant detection in anticoagulated patients. Guidance from the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the International Society on Thrombosis and Haemostasis.

    Tripodi A, Cohen H, Devreese KMJ

    Journal of thrombosis and haemostasis : JTH 2020; (18(7)):1569-1575 doi:10.1111/jth.14846.

    PMID: 32619349
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    Lupus-anticoagulant testing at NOAC trough levels.

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    Thrombosis and haemostasis 2016; (116(2)):235-40 doi:10.1160/TH16-02-0081.

    PMID: 27075441
  14. 14

    Laboratory testing for lupus anticoagulant (LA) in patients taking direct oral anticoagulants (DOACs): potential for false positives and false negatives.

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    Pathology 2019; (51(3)):292-300 doi:10.1016/j.pathol.2018.11.008.

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    Direct oral anticoagulant adsorption: Impact on lupus anticoagulant testing-Review of the literature and evaluation on spiked and patient samples.

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    The 2023 ACR/EULAR Antiphospholipid Syndrome Classification Criteria.

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    Diagnostic, research, and real-life effect of the 2023 EULAR-ACR classification criteria for antiphospholipid syndrome.

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  18. 18

    Insights into the 2023 ACR/EULAR antiphospholipid syndrome classification criteria: findings from a cohort of 205 patients with primary APS.

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    PMID: 39689033

This page explains antiphospholipid syndrome antibody testing for informational purposes only and does not replace professional medical advice. Your clinician and laboratory team should interpret your results and advise you on safe testing while taking anticoagulants.

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