Antiphospholipid Syndrome - APS

Diagnosis

Indications for Testing

  • Recurrent vascular thromboses, recurrent pregnancy loss, unexplained prolonged PTT in an asymptomatic patient (indication for lupus anticoagulant testing)
  • Additional indications for testing may also include the presence of endocarditis, livedo reticularis, thrombocytopenia, hemolytic anemia, and thrombotic microangiopathy

Criteria for Diagnosis

  • Revised classification criteria for antiphospholipid antibody syndrome
    Revised Classification Criteria for Antiphospholipid Antibody Syndrome
    (At least 1 clinical and 1 laboratory criterion must be met)

    Clinical criteria

    Vascular thrombosis – One or more clinical episodes of arterial, venous, or small-vessel thrombosis in any tissue or organ validated by imaging studies or histopathology

    Pregnancy morbidity

    • One or more unexplained deaths of a morphologically normal fetus after 10th week of gestation
    • One or more premature births of a morphologically normal neonate before the 34th week of gestation due to preeclampsia, eclampsia, or placental insufficiency
    • Three or more unexplained, consecutive, spontaneous abortions before 10th week of gestation, and with maternal anatomic or hormonal abnormalities and paternal and maternal chromosomal causes excluded

    Laboratory criteria

    Positive test on 2 or more occasions at least 12 weeks apart

    • Lupus anticoagulant – detected in plasma according to the guidelines of the International Society on Thrombosis and Hemostasis
    • aCL antibody – IgG and/or IgM isotype present in a medium or high titer (>40 GPL or MPL or >99th percentile), measured by standardized ELISA
    • Anti-β2GP1antibody – IgG and/or IgM isotype in high titer (>99th percentile), measured by standardized ELISA
    GPL – IgG phospholipid antibody; MPL – IgM phospholipid antibody; ELISA – enzyme-linked immunosorbent assay

Laboratory Testing

  • Current recommendations for first-line laboratory testing should include the following
    • LA activity
      • At least 2 phospholipid-dependent clotting assays, based on different principles, should be performed to identify LA activity
    • aCL IgG and IgM antibodies
    • β2GP1 IgG and IgM antibodies
    • Combination of all three tests reduces rate of false-positive results
    • Repeat positive laboratory tests after 12 weeks to confirm persistent positivity
    • Repeat testing if a strong clinical suspicion exists for APS but criteria laboratory tests are negative (seronegative APS)
  • Also consider the following non-criteria tests for patients with repeatedly negative results from criteria tests
    • aCL antibody, IgA
    • β2GP1 antibody, IgA
    • Phosphatidylserine antibodies, IgG, IgM, & IgA
    • Prothrombin antibodies, IgG and IgM

Differential Diagnosis

Screening

  • Not recommended for patients with single deep vein thrombosis unless a risk factor is present
  • Test for antibodies in the following situations
    • Thrombosis
      • Arterial thrombosis <50 years
      • Unprovoked venous thrombosis <50 years
      • Recurrent thrombosis
      • Thrombosis at unusual site
      • Patients with both arterial and venous thrombotic events
      • Patients admitted with thrombotic microangiopathy of unknown etiology
    • Obstetric manifestations
      • ≥1 unexplained fetal loss after 10th week of gestation
      • Unexplained severe intrauterine growth restriction
      • Early or severe preeclampsia
      • ≥3 spontaneous miscarriages before 10th week of gestation
    • Patients with SLE 
      • Perform baseline test
      • Repeat testing
        • Before pregnancy, surgery, transplantation, and use of estrogen-containing treatments
        • New neurologic, vascular or obstetric event present

Clinical Background

Antiphospholipid syndrome (APS) is an autoimmune disorder in which autoantibodies are directed against phospholipid-protein complexes. APS is characterized by thrombosis (arterial, venous, or small vessel) and/or pregnancy complications and persistently positive tests for antiphospholipid-protein (aPL) antibodies.

Epidemiology

  • Prevalence
    • Present in a small percentage of young healthy subjects (1-5%) and in up to 10% of patients with venous thrombosis
      • Estimates of prevalence are hampered by the variety of testing systems available for diagnosis
    • Higher prevalence in patients with connective tissue disease, but most patients with aPL antibodies do not have an underlying autoimmune disease

Risk Factors

  • Connective tissue disease
  • Infections – no increase in thrombotic risk
  • Malignancy
  • Liver disease
  • Vascular disease
  • Medications – increased thrombotic risk

Pathophysiology and Basis for Laboratory Tests

  • Proposed mechanisms for thrombosis include endothelial cell damage or activation, platelet activation, and interference with the function of anticoagulant protein function
  • LAs are autoantibodies that target complexes of phospholipids with either β2GP1 or another plasma protein such as prothrombin
    • LAs usually demonstrate an inhibitor effect in laboratory clotting tests by interfering with phospholipid-dependent clotting reactions
    • Prolongation of clotting times (apparent anticoagulation) is an in vitro laboratory phenomenon; in vivo thrombosis is much more common than bleeding
  • aPL antibodies are often classified as either lupus anticoagulant (LA), or anticardiolipin (aCL) antibodies, or anti-beta-2 glycoprotein 1 (β2GP1) antibodies
    • Thrombosis appears to be more common in patients with LA activity
    • Positivity for all 3 (LA activity, aCL and β2GP1 antibodies) is a strong independent risk factor for thrombosis
  • Transient aPL antibodies may occur in association with infections and with certain medications (procainamide, hydralazine, quinidine, chlorpromazine, penicillin)

Clinical Presentation

  • Venous, arterial, or small vessel thrombosis, and/or obstetric complications
  • Other potential abnormalities include cytopenias or other hematologic disorders, and neurologic, dermatologic, or cardiopulmonary abnormalities
  • Catastrophic APS is a multi-organ illness caused by diffuse small vessel thrombosis and tissue ischemia

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Antiphospholipid Syndrome Reflexive Panel 2003222
Method: Electromagnetic Mechanical Clot Detection/Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Recommended laboratory testing for APS

Components include β2GP1 antibodies, IgG & IgM; aCL antibodies, IgG & IgM; and LA reflexive panel

Refer to individual components

Positive results – confirm at least 12 weeks apart

Lupus Anticoagulant Reflexive Panel 0030181
Method: Electromagnetic Mechanical Clot Detection

Identify LA activity in patient with clinical features of APS or unexpected prolonged partial thromboplastin time results

Not recommended as stand-alone test for APS; for suspected APS, order along with

  • aCL antibodies, IgG & IgM
  • β2GP1 antibodies, IgG & IgM

Panel includes LA-sensitive PTT and dilute Russell Viper Venom (dRVVT) for screening, followed by mixing studies and confirmatory assays if indicated

No single testing system will identify 100% of LA activity

Anticoagulant therapy may interfere with test results

Negative results – consider repeat testing if clinical suspicion is high

Positive results – confirm at least 12 weeks apart

Cardiolipin Antibodies, IgG and IgM 0099344
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Diagnose APS

Not recommended as stand-alone test; order along with

  • LA reflexive panel
  • β2GP1 antibodies, IgG & IgM
False-positive results may occur with infectious and autoimmune diseases

Inconclusive results – consider repeat testing

Positive results – confirm at least 12 weeks apart

Beta-2 Glycoprotein 1 Antibodies, IgG and IgM 0050321
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Diagnose APS

Not recommended as stand-alone test; order along with

  • LA reflexive panel
  • aCL antibodies, IgG & IgM
 

Inconclusive results – consider repeat testing

Positive results – confirm at least 12 weeks apart

High-Specificity Antiphospholipid Antibodies, IgG and IgM 2005457
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Use to diagnose APS

More specific than cardiolipin IgG and IgM antibodies in diagnosis of APS

   
Non-Criteria Antiphospholipid Syndrome (APS) Antibody Panel 2005386
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Use only for selected cases of strongly suspected APS with negative initial testing

   
Antiphospholipid Antibodies Extended Panel 2007609
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Use only for selected cases of strongly suspected APS with negative initial testing

   
Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Beta-2 Glycoprotein 1 Antibody, IgA 0050324
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Cardiolipin Antibodies, IgG, IgM, and IgA 0051162
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

IgG and IgM panel test preferred

Cardiolipin Antibody, IgG 0050901
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

IgG and IgM panel test preferred

Cardiolipin Antibody, IgM 0050902
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

IgG and IgM panel test preferred

Cardiolipin Antibody, IgA 0098358
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Phosphatidylcholine Antibodies, IgG, IgM and IgA 0051590
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Phosphatidylethanolamine Antibodies, IgG, IgM and  IgA 0051622
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Phosphatidylinositol Antibodies, IgG, IgM and IgA 0051624
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Phosphatidylglycerol Antibodies, IgG, IgM and IgA 0051623
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Phosphatidylserine and Prothrombin Antibody, IgG 2009447
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

May be useful as an independent risk marker for thrombosis associated with APS and related diseases

Consider testing if all criteria aPL antibody tests are negative; positive results should be reported to document persistence

Phosphatidylserine and Prothrombin Antibodies, IgG and IgM 2009451
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

May be useful as an independent risk marker for thrombosis associated with APS and related diseases

Consider testing if all criteria aPL antibody tests are negative; positive results should be reported to document persistence

Phosphatidylserine Antibodies, IgG and IgM 2006495
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Phosphatidylserine Antibodies, IgG, IgM, and IgA 0050905
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Prothrombin Antibody, IgG 0051302
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Prothrombin Antibody, IgM 0051303
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Prothrombin Antibodies, IgG & IgM 2004411
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Not recommended

Dilute Russell Viper Venom Time (dRVVT) with Reflex to dRVVT 1:1 Mix and Confirmation 0030461
Method: Electromagnetic Mechanical Clot Detection

Preferred test is the LA reflexive panel 

Thrombotic Risk (Acquired) Reflexive Panel 0030268
Method: Electromagnetic Clot Detection/Semi-Quantitative Enzyme-Linked Immunosorbent Assay/Immunoturbidimetry/Quantitative Enzymatic

If PTT and dRVVT are normal, then no further testing is performed; if PTT is abnormal, Thrombin Time is added; if Thrombin Time is normal, PTT 1:1 mix is added;  if Thrombin time is abnormal, Reptilase Time and PTT Heparin Neutralization is added

If PTT Heparin Neutralization is abnormal, PTT 1:1 mix is added; if PTT 1:1 mix is abnormal, Platelet Neutralization procedure is added; if dRVVT is abnormal, dRVVT 1:1 mix is added; if dRVVT 1:1 mix is abnormal, dRVVT confirmation is added; if Platelet Neutralization procedure and dRVVT confirmation are normal or if one is normal and the other not done, Hexagonal Phospholipid Neutralization is added

Hexagonal Phospholipid Neutralization 0030064
Method: Qualitative Clotting

Preferred test is the LA reflexive panel