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Phosphatidylserine-Prothrombin Antibodies, IgG, IgM

Test Code(s) 11443, 11446, 11447

Antiphospholipid syndrome (APS) is a disease state that includes at least 1 clinical event and at least 1 persistently positive antiphospholipid antibody result (tested >12 weeks apart).1 The classification criteria for APS are shown in the following table.

Table. Classification Criteria for Antiphospholipid Syndrome1

a A positive cardiolipin antibody result is defined as a result greater than the 99th percentile of a normal population, or medium to high titer antibodies (>40 GPL or MPL) if the cutoff does not reflect the 99th percentile.1

b Pregnancy morbidity refers to 1 of the following: (1) 3 consecutive pregnancy losses <10 weeks of gestation,

(2) >1 fetal death >10 weeks of gestation, or (3) >1 preterm delivery for severe preeclampsia and/or placental insufficiency.2

According to the 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, ß2-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 (eg, because of livedo reticularis, recurrent transient ischemic attacks, leg ulcers, and/or history of lupus erythematosus), testing for non-criteria antiphospholipid antibodies, such as phosphatidylserineprothrombin (PSPT) antibodies, may be considered to support the diagnosis of APS.3-5 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.

The assay is intended for the detection of IgG and IgM class antibodies to phosphatidylserine/prothrombin 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 PS–PT antibody test result may be useful in contributing to the diagnosis of APS and stratifying patients for thrombosis risk.6 PS–PT IgM and IgG antibody (non-criteria APS antibodies) positivity is highly correlated with the presence of LAs,7 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.8 PS–PT antibody testing may be a useful surrogate for LA for patients who are receiving these anticoagulant therapies.9   

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).8


  1. 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
  2. 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
  3. 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
  4. 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
  5. 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
  6. 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
  7. 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
  8. 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
  9. 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.



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