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Phosphatidylserine-Prothrombin Antibodies, IgG, IgM

Test Codes: 11443, 11446, 11447

Antiphospholipid syndrome (APS) is a systemic autoimmune disease characterized by arterial, venous, or microvascular thrombosis, pregnancy morbidity, or nonthrombotic manifestations in patients with persistent antiphospholipid antibodies (aPL).

In 2023, the American College of Rheumatology (ACR) and the European Alliance of Associations for Rheumatology (EULAR) published an update to the classification of APS.1 The new criteria include 1 positive aPL test within 3 years of identifying an aPL-associated clinical criterion, followed by additive weighted criteria (score range 1-7 points each) clustered into 6 clinical domains and 2 laboratory domains (Table below: 2023 ACR/EULAR Classification Criteria for Antiphospholipid Syndrome1). Patients classified as having APS if they accumulate at least 3 points from the clinical domains and at least 3 points from the laboratory domains.

Compared to the 2006 revised Sapporo classification criteria,2 the 2023 ACR/EULAR APS classification had an improved specificity of 99% versus 86% but a reduced sensitivity of 84% versus 99%, respectively.

Click table to open in new window (enlarged)

According to the antiphospholipid syndrome (APS) classification criteria, laboratory diagnosis of APS requires detection of at least 1 of the antiphospholipid antibodies shown in the table in question 1 (cardiolipin IgG or IgM, b2-glycoprotein I IgG or IgM, or lupus anticoagulant [LA]), the so-called “criteria” antibodies.

However, if criteria antibody test results are negative and APS is still strongly suspected (because of livedo reticularis, recurrent transient ischemic attacks, leg ulcers, and/or history of lupus erythematosus), testing for non-criteria antiphospholipid antibodies, such as phosphatidylserine–prothrombin (PS–PT) antibodies, may be considered supportive of the diagnosis of APS.4-6 The greater the number of non-criteria antibodies, especially in the presence of appropriate clinical findings, the greater the probability of identifying APS. PS-PT antibodies are among the few non-criteria antibodies that have a strong association with APS.4-6

Furthermore, positive IgG or IgM PS-PT antibodies along with the “criteria” antibodies (cardiolipin IgG or IgM, b2-glycoprotein I IgG or IgM, or lupus anticoagulant [LA]) is called “quadruple-positive” APS and may be independently associated with a significantly higher risk of organ damage in a subgroup of patients.7 

The assay is intended for the detection of IgG and IgM class antibodies to the PS-PT complex in serum or plasma. Results are reported in IgG and IgM units. A positive result indicates the presence of PS–PT IgG or IgM antibodies and suggests the possibility of certain autoimmune disease thrombotic disorders, such as APS, or those secondary to systemic lupus erythematosus or other lupus-like thrombotic diseases. As there is a lack of international standards for testing, results obtained with different manufacturers’ assay methods may not be used interchangeably.

A positive phosphatidylserine-prothrombin (PS–PT) antibody test result may help diagnose APS and stratify patients for thrombosis risk.8 PS–PT IgM and IgG antibody (non-criteria APS antibodies) positivity is highly correlated with the presence of LAs,9 a heterogeneous group of antibodies directed against protein-phospholipid complexes. LAs are characterized by their ability to prolong phospholipid-dependent clotting assays.

One limitation of LA detection is that many of the direct oral anticoagulant therapies (eg, direct factor Xa and thrombin inhibitors) interfere with testing and may cause false-positive LA results.10 PS–PT antibody testing may be a potential surrogate for LA for patients who are receiving these anticoagulant therapies.11   

Not necessarily. The designated IgG/IgM cutoff of ≤30 units is an optimal cutoff for sensitivity and specificity for APS based on the manufacturer’s studies. This cutoff may represent the 99th percentile of the normal population, depending on the characteristics of the normal population studied. 

No, PS–PT antibody testing is performed using an enzyme-linked immunoassay (ELISA)-based method, and anticoagulants do not interfere with ELISA testing. Therefore, PS–PT test results are not affected by anticoagulants such as vitamin K antagonists (eg, warfarin), heparins (low molecular weight and unfractionated), direct thrombin inhibitors (eg, dabigatran), and anti-Xa medications (eg, rivaroxaban, apixaban, edoxaban). In contrast, as noted above, anticoagulants may affect the results of LA testing (depending on the level of and type of anticoagulant).10

References

  1. Barbhaiya M, Zuily S, Naden R, et al. The 2023 ACR/EULAR Antiphospholipid Syndrome Classification Criteria. Arthritis Rheumatol. 2023;75(10):1687-1702. doi:10.1002/art.42624
  2. Miyakis S, Lockshin MD, Atsumi T, et al. International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS). J Thromb Haemost. 2006;4(2):295-306. doi:10.1111/j.1538-7836.2006.01753.x
  3. Arslan E, Branch DW. Antiphospholipid syndrome: diagnosis and management in the obstetric patient. Best Pract Res Clin Obstet Gynaecol. 2020;64:31-40. doi:10.1016/j.bpobgyn.2019.10.001
  4. Zohoury N, Bertolaccini ML, Rodriguez-Garcia JL, et al. Closing the serological gap in the antiphospholipid syndrome: the value of "non-criteria" antiphospholipid antibodies. J Rheumatol. 2017;44(11):1597-1602. doi:10.3899/jrheum.170044
  5. Pignatelli P, Ettorre E, Menichelli D, et al. Seronegative antiphospholipid syndrome: refining the value of "non-criteria" antibodies for diagnosis and clinical management. Haematologica. 2020;105(3):562-572. doi:10.3324/haematol.2019.221945
  6. Litvinova E, Darnige L, Kirilovsky A, et al. Prevalence and significance of non-conventional antiphospholipid antibodies in patients with clinical APS criteria. Front Immunol. 2018;9:2971. doi:10.3389/fimmu.2018.02971
  7. Hoxha A, Gobbo G, Gavasso S, et al. Antiphosphatidylserine/prothrombin antibodies define a high-risk antiphospholipid syndrome profile associated with organ damage. Clin Chem Lab Med. Published online February 3, 2026. doi:10.1515/cclm-2025-1565
  8. Heikal N, Martins TB, White SK, et al. Laboratory evaluation of antiphospholipid syndrome: is there a role for specific noncriteria antiphospholipid antibody tests? Am J Clin Pathol. 2019;152(5):638-646. doi:10.1093/ajcp/aqz085
  9. Vlagea A, Gil A, Cuesta MV, et al. Antiphosphatidylserine/prothrombin antibodies (aPS/PT) as potential markers of antiphospholipid syndrome. Clin Appl Thromb Hemost. 2013;19(3):289-296. doi:10.1177/1076029612437578
  10. Adcock DM, Gosselin R. Direct oral anticoagulants (DOACs) in the laboratory: 2015 review. Thromb Res. 2015;136(1):7-12. doi:10.1016/j.thromres.2015.05.001
  11. Pengo V. Additional tests to improve on the diagnosis of antiphospholipid syndrome. J Thromb Haemost. 2020;18(8):1846-1848. doi:10.1111/jth.14896

 

This FAQ is provided for informational purposes only and is not intended as medical advice. Test selection and interpretation, diagnosis, and patient management decisions should be based on the physician’s education, clinical expertise, and assessment of the patient.

 

 

Document FAQS.262 Version: 1

Version 1: Effective 09/09/2026 to present

Version 0: Effective 08/11/2022 to 09/09/2026

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