Diagnosis of the antiphospholipid syndrome“
INTRODUCTION — The antiphospholipid syndrome (APS) is defined by two major components:
- Presence in the serum of at least one type of autoantibody known as an antiphospholipid antibody (aPL). APLs are directed against phospholipid-binding plasma proteins.
- The occurrence of at least one clinical feature from a diverse list of potential disease manifestations, the most common of which are categorized as venous or arterial thromboses, and pregnancy morbidity.
Although the clinical manifestations of APS occur in other disease populations, in the APS they occur by definition in the context of aPL. APL may be detected by:
- Lupus anticoagulant tests
- Anticardiolipin antibody ELISA
- Anti-ß2 glycoprotein-I ELISA
The full clinical significance of other autoantibodies, including those directed against prothrombin, annexin V, phosphatidylserine, and phosphatidylinositol, remain unclear.
APS occurs either as a primary condition or in the setting of an underlying disease, particularly systemic lupus erythematosus (SLE).
The classification criteria diagnosis of the APS will be reviewed here. The pathogenesis, clinical manifestations, and treatment of this disorder are presented separately. (See “Pathogenesis of the antiphospholipid syndrome” and “Clinical manifestations of the antiphospholipid syndrome” and “Treatment of the antiphospholipid syndrome”.)
CLASSIFICATION (RESEARCH) CRITERIA — Classification criteria have been developed for research purposes. They may be helpful to clinicians, but not all the classification criteria need to be met to make a clinical diagnosis of APS.
International consensus conferences have proposed  and revised  classification criteria for definite APS. These are often referred to as the Sapporo criteria. Definite APS is considered present if at least one of the following clinical criteria and at least one of the following laboratory criteria are satisfied.
- Clinical — One or more episodes of venous, arterial, or small vessel thrombosis and/or morbidity with pregnancy.
- Thrombosis — Unequivocal imaging or histologic evidence of thrombosis in any tissue or organ, OR
- Pregnancy morbidity — Otherwise unexplained death at ≥10 weeks gestation of a morphologically normal fetus, OR
- One or more premature births before 34 weeks of gestation because of eclampsia, preeclampsia, or placental insufficiency, OR
- Three or more embryonic (<10 week gestation) pregnancy losses unexplained by maternal or paternal chromosomal abnormalities or maternal anatomic or hormonal causes.
- Laboratory — The presence of antiphospholipid antibodies (aPL), on two or more occasions at least 12 weeks apart and no more than five years prior to clinical manifestations, as demonstrated by one or more of the following :
- IgG and/or IgM aCL in moderate or high titer (>40 units GPL or MPL or > 99th percentile for the testing laboratory)
- Antibodies to ß2-glycoprotein-I (ß2-GP-I) of IgG or IgM isotype at a titer >99th percentile for the testing laboratory when tested according to recommended procedures [3,4].
- Lupus anticoagulant (LA) activity detected according to published guidelines [5,6].
EVALUATION OF THE SAPPORO CRITERIA — Two evaluations of the proposed and revised Sapporo criteria have been conducted [7,8]. In a retrospective analysis  of 200 aPL-positive patients who met the 1999 Sapporo criteria , only 59 percent met the 2006 revised criteria . Thus, although the revised criteria are useful in defining a more homogeneous population for the purposes of research studies, it is likely that they exclude a significant number of patients believed to have the APS clinically. Additional evaluations of the reliability and discriminatory testing of the revised Sapporo criteria are recommended before broad application .
DIAGNOSIS — Clinical suspicion for APS should be raised in the following scenarios:
- Occurrence of one or more otherwise unexplained thrombotic or thromboembolic events
- One or more specific adverse outcomes related to pregnancy, as defined in the preceding section
- Otherwise unexplained thrombocytopenia or prolongation of a test of blood coagulation (eg, PT or aPTT).
The APS may be considered present in a patient with only one thrombotic event and a positive aPL assay (see ‘Classification (research) criteria’ above) that is verified on at least two occasions at least 12 weeks apart . However, some investigators argue that the diagnosis cannot be made with certainty in patients with a single episode of venous thrombosis, especially in the presence of other thrombotic risk factors, in whom the presence of aPL may be an incidental finding rather than a causal event. This is particularly true with aCL.
Elevated levels of IgG or IgM aCL as well as a positive LA test can occur in otherwise normal individuals. In one study, for example, the prevalence of IgG and IgM aCL was 6.5 and 9.4 percent, respectively, on a first test in 522 randomly selected normal blood donors .
Although the occurrence of aCL is not uncommon in healthy subjects, repeatedly positive tests, which are required to meet the criteria for APS, are uncommon. In the above report, only 22 and 14 percent of those with an initial positive test (ie, 1.4 and 1.3 percent of the total population) remained positive for nine months .
Another concern is that a positive test for aPL in a patient with suspected venous thromboembolism does not prove a causal relationship. This was illustrated in a study of 65 patients with a first venous thromboembolic event and 179 patients with a suspected event who did not have a thrombus . The prevalence of IgG aCL was similar in the two groups (14 versus 18 percent at >30 GPL units and 6.2 versus 3.4 percent at >50 GPL units). In comparison, LA activity was much more common in the patients with venous thromboembolism (14 versus 1.7 percent).
Assays for antiphospholipid antibodies — A history of a biologic false positive serologic test for syphilis (BFPTS) may be a clue to the presence of any type of aPL: aCL, ß2-GP-I antibodies, or an LA. However, because of the nonspecific nature of the BFPTS, the presence of one or more aPL should be confirmed with one of the tests indicated below [3,11-13].
The presence of aPL may be demonstrated directly by:
- ELISA testing in the case of aCL and antibodies to ß2-GP-I.
- Clotting assay that demonstrates effects of an aPL on the phospholipid-dependent factors in the coagulation cascade (LA test).
ACL and ß2-GP-I assays — APL binding to phospholipids is mediated through nonimmunoglobulin phospholipid-binding plasma proteins. ß2-GP-I is the main antigenic target of aPL. Some experienced clinical laboratories can distinguish between:
- Antibodies to cardiolipin and other phospholipids.
- Antibodies to cardiolipin that require the presence of ß2-GP-I for binding and those that do not. However, such assays are not generally commercially available.
- Antibodies binding to ß2-GP-I that are independent of the presence of phospholipids, and those for which phospholipids are required
Antibody levels for aCL of IgG and IgM type are reported in units as GPL and MPL, respectively. Recommendations for a standard approach to testing and reporting were published in 2001 . (See “Pathogenesis of the antiphospholipid syndrome”, section on ‘Antiphospholipid antibodies’.)
Lupus anticoagulant — The lupus anticoagulant phenomenon refers to the ability of aPL to cause prolongation of in vitro clotting assays such as the activated partial thromboplastin time (aPTT), the dilute Russell viper venom time (dRVVT), the kaolin clotting time or, infrequently, the prothrombin time. This prolongation is not reversed when the patient’s plasma is diluted 1:1 with normal platelet-free plasma. In contrast, such mixing studies do correct the clotting abnormality associated with factor deficiencies.
One common effect of aPL detected by routine laboratory testing is the prolongation of the aPTT. However, only about one-half of patients with LAs have prolongations of the aPTT. Thus, if APS is suspected strongly, additional testing, usually with a dRVVT, is essential.
In 2009, an International committee recommended the following updated guidelines for the detection of LAs ; an additional explanation of technical details can be found in an excellent review .
- Blood should be collected before initiation of an anticoagulant medication. Blood should be collected in 0.109 M sodium citrate 9:1.
- Both patient and normal plasma should be as platelet-free as possible. For testing on fresh plasma, frozen samples, and pooled normal plasma, the platelet count should be less than 10,000/microL. Platelet filtration, the preferred method for preparing platelet-free plasma, may interfere with testing of other coagulation factors.
- Two or more tests should be used to screen for LAs . The most commonly used assays are the dRVVT and the dilute activated PTT (dAPTT). Other tests include the kaolin clotting time (KCT) and the dilute prothrombin time (dPT) . An LA is present if any of the tests is positive .
- Inhibitor activity should be documented by the effect of patient plasma on pooled normal plasma. Confirmatory studies need to be performed to document the phospholipid dependence of the inhibitor.
Laboratory experience is important in LA assays. In one study, one quarter of all plasma samples diagnosed as having LA activity were found to be false-positive tests upon measurement in a reference laboratory .
Detection of LA during anticoagulation — A common clinical issue is testing for an LA in a patient who is already on anticoagulant therapy.
- Although it is controversial, some experts believe that LA activity can be detected in patients treated with warfarin if the INR is <3.5, while others believe that the LA test should not be ordered in anticoagulated patients . In the setting of warfarin anticoagulation, the patient plasma is diluted 1:2 with normal plasma before testing. Other techniques to circumvent this problem include using paired phospholipid-dependent tests on undiluted index plasmas and using paired tests based on snake venoms .
- Low molecular weight heparin may interfere with LA detection, particularly if anti-factor Xa activity is over the therapeutic range [15,17]. The likelihood of an effect may depend upon the low molecular weight heparin preparation used .
- Treatment with unfractionated heparin may cause false positive tests for LAs .
Clinical significance of aPL type — The clinical significance of different antibodies specificities is uncertain. Some studies have suggested that LA positivity incurs a somewhat greater risk for thrombosis than aCL. Other studies indicate that antibodies to ß2-GP-I mediate the pathogenicity of aPL in a sizeable subset of patients with the APS. Thus, aCL and LAs alone may fail to induce the APS, but when directed against ß2-GP-I often lead to development of the full-blown disorder. The risk of thromboembolic events may vary with immunoglobulin class and isotype. (See “Pathogenesis of the antiphospholipid syndrome”.)
aPL titer and APS risk — The risk of thromboembolic phenomena may increase with the level of aPL and with the number of different aPL specificities present in a particular person. This was illustrated in a case-control study of 208 patients suspected of having APS and an equal number of age and gender matched controls . Each 10 U increase in IgM or IgG aCL was associated with a 5 to 7 percent increase in risk of thromboembolism. Furthermore, each additional aPL specificity (eg, aCL alone versus aCL plus LA versus aCL plus LA plus anti-ß2-GP-I) was associated with a 50 to 70 percent increase in the odds of arterial or venous thromboembolic events.
Approach to diagnosis — A thorough medical history, physical examination, and selected laboratory testing are necessary to diagnose the APS.
History — The history should be focused on the nature and frequency of thromboembolic events, the outcomes of pregnancies in female patients, other thrombosis risk factors, and the use of medications known to induce aPL. (See “Pathogenesis of the antiphospholipid syndrome”, section on ‘Medications’.)
Medications known to be associated with aPL production include the phenothiazines, hydralazine, procainamide, and phenytoin. However, because these medications usually do not lead to the production of antibodies to ß2-GP-I, they are generally not associated with clinical events.
A review of systems should allow an associated illness to be suspected or excluded. The most important is systemic lupus erythematosus. (See “Pathogenesis of the antiphospholipid syndrome”, section on ‘Autoimmune and rheumatic diseases’.)
Physical examination — There are no pathognomonic physical findings of APS. Abnormal features may be found on examinations that are related to ischemia or infarction of the skin, viscera, or nervous system. Physical examination findings may include the presence of livedo reticularis (and particularly livedo racemosa) (picture 1), digital ischemia, gangrene, deep venous thrombosis, or neurological lesions consistent with a stroke. (See “Clinical manifestations of the antiphospholipid syndrome”.)
Laboratory testing — One or more of the following laboratory tests for the presence of aPL or for evidence of their activity as LAs supports the diagnosis  (see ‘Assays for antiphospholipid antibodies’ above):
- Moderate to high titer IgG and IgM aCL
- Moderate to high titer IgG and IgM anti-ß2-GP-I
- LA test (dRVVT and dAPTT or other combination as the screening tests)
The following are important points to consider in the interpretation of aPL tests, since diagnosis of APS requires clinical manifestations as well as presence of aPL:
- False positive tests — Transient aCL, usually in low titer, have been reported in up to 10 percent of healthy blood donors on initial testing, but persist on repeat testing in only about 1.5 percent of individuals . Thus, before making the diagnosis of APS, the persistence of aPL should be demonstrated and the clinical scenario must be judged to be concordant with the test finding.
- False negative tests — Some patients with clinical features consistent with APS do not have detectable aCL, anti-ß2-GP-I antibodies, or a positive LA test, especially at the time of thrombosis. Other aPL tests that can be considered in this setting are those directed against phosphatidylserine, phosphatidylinositol, and prothrombin [3,19]. However, little is known about the sensitivity, specificity, and clinical significance of testing for these antibodies. Thus, if the initial aPL tests (aCL, anti-ß2-GP-I, LA test) are negative, screening for heritable and acquired disorders of coagulation (eg, clotting factor deficiencies) should be strongly considered before ordering additional aPL tests. (See ‘Differential diagnosis’ below and “Evaluation of the patient with established venous thrombosis”, section on ‘Screening for inherited thrombophilia’.)
- Repeat testing — Transiently increased aCL may occur in the setting of viral or other infections. A confirmatory aCL, anti-ß2-GP-I, or LA test obtained at least 12 weeks after the initial positive test increases confidence in the diagnosis of APS. (See “Pathogenesis of the antiphospholipid syndrome”, section on ‘Infections’.)
Differential diagnosis — The differential diagnosis depends upon the presenting clinical manifestations. Many acquired and genetic disorders may result in pregnancy loss, thromboembolic disease, or both. It must also be remembered that aPL may coexist with other conditions and have a synergistic effect on the development of clinical events.
Presence of aPL — Various aPL may be present in some people who are otherwise healthy, have autoimmune or rheumatic disease, have been exposed to certain drugs or infectious agents. These and other associations are discussed in more detail elsewhere. (See “Pathogenesis of the antiphospholipid syndrome”, section on ‘Prevalence in different conditions’.)
Recurrent pregnancy loss — The differential diagnosis of recurrent pregnancy loss is presented separately. (See “Evaluation of couples with recurrent pregnancy loss”.)
The differential diagnosis varies depending upon the vascular bed involved: venous, arterial, or both .
Venous thrombosis — If the manifestations are exclusively those of venous thrombosis or pulmonary embolic disease, the differential diagnosis includes the following conditions:
- Inherited and acquired coagulation and anticoagulation factor disorders (eg, protein C and protein S deficiency, factor V Leiden deficiency)
- Defective clot lysis
- Cancer and myeloproliferative disorders
- Nephrotic syndrome
The list of risk factors known to be associated with venous thrombosis continues to expand. (See “Overview of the causes of venous thrombosis”.)
Arterial thrombosis — When only the arterial bed is affected, the following disorders must be excluded:
- Embolic disease
- Atrial fibrillation or, much less common, atrial myxoma
- Marked left ventricular dysfunction
- Cholesterol emboli
- Paradoxical embolism
- Decompression sickness (Caisson’s disease)
- Thrombotic thrombocytopenic purpura/hemolytic-uremic syndrome
- Polyarteritis nodosa and other forms of systemic vasculitis
Complete testing for inherited thrombophilias is not justified in patients presenting only with arterial thrombosis, since these disorders are primarily associated with venous thrombosis. (See “Overview of the causes of venous thrombosis”.)
Demyelinating disease is a consideration when the white matter of the central nervous system is affected.
Arterial and venous thrombosis — A combination of arterial and venous thrombosis, either simultaneously or sequentially, suggests the following diseases, which are discussed elsewhere on the appropriate topic reviews:
- Heparin-induced thrombocytopenia
- Defective clot lysis due to dysfibrinogenemia or plasminogen activator deficiency
- Myeloproliferative disorders, polycythemia vera (P vera), or paroxysmal nocturnal hemoglobinuria
- Hyperviscosity due to P vera, Waldenstrom’s macroglobulinemia, sickle cell disease
- Systemic vasculitis, such as those associated with antineutrophil cytoplasmic antibodies
- Paradoxical embolism
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)
- Beyond the Basics topics (see “Patient information: The antiphospholipid syndrome”)
- The antiphospholipid antibody syndrome (APS) is defined by two major components:
- The occurrence of at least one clinical feature from a diverse list of potential disease manifestations, the most common of which are venous or arterial thromboses and recurrent fetal loss.
- Persistent presence in the serum of at least one type of antiphospholipid antibody (aPL).
- Both clinical and laboratory criteria are required for the diagnosis of APS. (See ‘Classification (research) criteria’ above.)
- APL are directed against serum proteins bound to anionic phospholipids and may be detected by (see ‘Assays for antiphospholipid antibodies’ above):
- Lupus anticoagulant test
- Anticardiolipin antibody ELISA
- Anti-ß2 glycoprotein-I ELISA
- Clinical suspicion for APS should be raised in the following scenarios:
- Occurrence of one or more otherwise unexplained thrombotic or thromboembolic events.
- One or more specific adverse outcomes related to pregnancy as defined above. (See ‘Classification (research) criteria’ above.)
- Otherwise unexplained thrombocytopenia or prolongation of a test of blood coagulation (eg, PT or aPTT).
- The presence of aCL and antibodies to ß2-GP-I may be demonstrated directly by:
- ELISA testing. (See ‘ACL and ß2-GP-I assays’ above.)
- Clotting assay (LA test) that demonstrates effects of these antibodies on the phospholipid-dependent factors in the coagulation cascade. The most common screening tests employed as the first step of a LA test are aPTT, the dilute Russell viper venom time (dRVVT), and the dilute activated partial thromboplastin time (daPTT). A prolonged screening test alone is not adequate for LA positivity; confirmatory steps with mixing studies (in order to rule out factor deficiencies) and additional phospholipid reagents (to demonstrate phospholipid dependence) are also required. (See ‘Lupus anticoagulant’ above.)