A contribution to the debate on the laboratory criteria that define the antiphospholipid syndrome

Semiquantitative interpretation of anticardiolipin and antiβ2glycoprotein I antibodies measured with various analytical platforms: Communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

BACKGROUND

Antiβ2glycoprotein I (aβ2GPI) and anticardiolipin (aCL) IgG/IgM show differences in positive/negative agreement and titers between solid phase platforms. Method-specific semiquantitative categorization of titers could improve and harmonize the interpretation across platforms.

AIM

To evaluate the traditional 40/80-unit thresholds used for aCL and aβ2GPI for categorization into moderate/high positivity with different analytical systems, and to compare with alternative thresholds.

MATERIAL AND METHODS

aCL and aβ2GPI thresholds were calculated for two automated systems (chemiluminescent immunoassay [CLIA] and multiplex flow immunoassay [MFI]) by receiver operating characteristic curve analysis on 1108 patient samples, including patients with and without antiphospholipid syndrome (APS), and confirmed on a second population (n = 279). Alternatively, regression analysis on diluted standard material was applied to identify thresholds. Thresholds were compared to 40/80 threshold measured by an enzyme-linked immunosorbent assay (ELISA). Additionally, likelihood ratios (LR) were calculated.

RESULTS

Threshold levels of 40/80 units show poor agreement between ELISA and automated platforms for classification into low/moderate/high positivity, especially for aCL/aβ2GPI IgG. Agreement for semiquantitative interpretation of antiphospholipid antibodies (aPL) IgG between ELISA and CLIA/MFI improves with alternative thresholds. LR for aPL IgG increase for thrombotic and obstetric APS based on 40/80 thresholds for ELISA and adapted thresholds for the other systems, but not for IgM.

CONCLUSION

Use of 40/80 units as medium/high thresholds is acceptable for aCL/aβ2GPI IgG ELISA, but not for CLIA and MFI. Alternative semiquantitative thresholds for non-ELISA platforms can be determined by a clinical approach or by using monoclonal antibodies. Semiquantitative reporting of aPL IgM has less impact on increasing probability for APS.

Thrombotic risk in antiphospholipidic syndrome: From hypothesis to current evidence (Review)

Thirty-five years after it was first described, antiphospholipid syndrome (APS) is unanimously recognized as a systemic autoimmune disease, a major acquired thrombophilia, which can affect any arterial or venous vascular territory, explaining the great diversity of clinical manifestations. The current classification criteria updated in the International Consensus Statement for Definite Antiphospholipid Syndrome from Sydney cannot explain alone the unpredictable evolution with thrombotic events of the patients diagnosed with APS. Although the link to genetics and epigenetics has not been clearly defined as in other autoimmune diseases, it is clear that a proper stratification of thrombotic risk in the era of personalized medicine must include classic biological markers (antiphospholipid antibodies, aPL), along with the already recognized phenotypes, non-conventional serological markers, and additional genetic risk factors for thrombosis. Moreover, with advancing age, a patient with APS develops other thrombotic risk factors which include: hypertension and dyslipidemia among others. According to the classification criteria, a patient is considered to have a low, moderate or high thrombotic risk. In clinical practice, patients with the same risk score may have completely different evolutions in terms of the recurrence of thrombosis. Concerning this approach, it appears that new non-conventional serological markers, phenotype-assessment and genetic determinants have an increasing importance and should be reconsidered in a proper thrombotic risk evaluation in patients with APS, compared to the initial concept of APS as first defined.

The (non-)sense of detecting anti-cardiolipin and anti-β2glycoprotein I IgM antibodies in the antiphospholipid syndrome

BACKGROUND

The antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy morbidity with the persistent presence of lupus anticoagulant (LAC), anti-cardiolipin (aCL) and/or anti-β2glycoprotein I (aβ2GPI) antibodies of the immunoglobulin G/immunoglobulin M (IgG/IgM) isotype. However, the role of aCL and aβ2GPI IgM as a serologic marker in APS is debated.

OBJECTIVES

We aimed to assess the diagnostic and clinical value of IgM antiphospholipid antibodies (aPL) in APS within the classification criteria.

PATIENTS/METHODS

Our multicenter study comprised 1008 patients, including APS patients and controls. Anti-CL and aβ2GPI IgG and IgM antibodies were detected with four commercially available solid phase assays.

RESULTS

Positivity for aCL and/or aβ2GPI antibodies was significantly correlated with thrombosis and pregnancy morbidity, independent of the isotype and solid phase assay. Higher odds ratios were obtained for IgG compared to IgM positivity. Isolated IgM was rare in thrombotic APS, but more frequent in obstetric APS, ranging from 3.5% to 5.4% and 5.7% to 12.3%, respectively, dependent on the solid phase assay. In a multivariate logistic regression analysis of aPL, IgM positivity was found to be associated with pregnancy morbidity. However, detection of IgM was not independently associated with thrombosis. Combined positivity for LAC, IgG, and IgM was highly associated with thrombosis and pregnancy morbidity.

CONCLUSIONS

Our data support testing for aCL and aβ2GPI IgM in women suspected of obstetric APS. However, no added value was found for testing IgM in patients suspected of thrombotic APS. Still, IgM aPL might be useful as a second-line test to improve thrombotic risk stratification.

IgG/IgM antiphospholipid antibodies present in the classification criteria for the antiphospholipid syndrome: a critical review of their association with thrombosis

Essentials The clinical value of IgM antibodies in thrombotic antiphospholipid syndrome (APS) is debated. By review of literature, we reconsidered the clinical value of IgM antibodies in thrombotic APS. More significant correlations with thrombosis were found for the IgG compared to IgM isotype. Unavailability of paired IgG/IgM results hampers evaluating the added value of IgM positivity. Click to hear Dr de Groot's perspective on antiphospholipid syndrome

SUMMARY

Background Despite the update of the classification criteria for the antiphospholipid syndrome (APS), difficulties persist in the identification of patients at risk for thrombosis. Current guidelines include assays detecting IgG/IgM anti-β2 -glycoprotein I and anti-cardiolipin antibodies, although the relevance of IgM antibodies has been debated. Objectives Through a review of the literature from 2001 to 2014, we aimed to formally establish the thrombotic risk stratification potential of IgM as compared with IgG anti-phospholipid antibodies (aPLs). Patients/methods One thousand two hundred and twenty-eight articles were selected by a computer-assisted search of the literature. Of the 177 studies that met our inclusion criteria, the clinical value of IgG/IgM aPLs was established through analysis of odds ratios for thrombosis or percentage of positives in the thrombotic population. Results/conclusions We clearly found more significant correlations with thrombosis for the IgG than for the IgM isotype. Nonetheless, in a minority of studies, significant associations with thrombosis were found for IgM but not IgG antibodies. The unavailability of paired results of IgG and IgM for each separate patient hampers evaluation of the added value of isolated IgM positivity. To fully take advantage of results obtained by future studies, we strongly encourage scientists to provide all studied information per patient. We planned a large multicenter study to investigate clinical associations of isolated/combined positivity for criteria/non-criteria aPLs. Importantly, because of the presence of non-pathogenic aPLs, quantitative assays are characterized by a high false-positivity rate. Optimization of functional assays, such as thrombin generation measuring the whole scheme of coagulation, may help to reduce APS-related morbidity and mortality.

Triple positive antiphospholipid antibody profile in outpatients with tests for lupus anticoagulants

BACKGROUND

A triple positive antiphospholipid (aPL) antibody profile [two positive serum IgG aPL antibodies along with one positive functional plasma lupus anticoagulant (LAC) test result] is associated with an increased risk for thrombosis, whereas patients with single positive test results may have little to no increased risk. The frequency of triple positivity in outpatients with various combinations of LAC test results is unclear.

METHODS

We extracted from our database all LAC test results [dilute Russell viper venom times (dRVVT) and silica clotting times (SCT)] that had concomitant serum IgG aPL testing [both serum anti β2-glycoprotein I (anti-β2GPI) and anti-cardiolipin (aCL) antibodies].

RESULTS

There were 3195 patients without a prolonged prothrombin time. Double antibody positivity was found in 1% (31/2955) of those with normal functional LAC test results, in 16.0% (31/81) of those with a positive dRVVT, in 12.7% (10/79) of those with a positive SCT, and in 56.3% (45/80) of those with both tests positive (p<0.001). A triple positive aPL antibody profile was found in 28.3% (68/240) of those with at least one positive LAC test result.

CONCLUSIONS

We conclude that 28% of patients with elevated LAC tests have a triple positive aPL antibody profile and patients with two positive LAC tests have a higher prevalence of a triple positive profile than do those with one positive LAC test result.

Antiphospholipid syndrome: a clinical and laboratorial challenge

Antiphospholipid syndrome (APS) is an acquired autoimmune thrombophilia characterized by the presence of a heterogeneous family of antibodies that bind to plasma proteins with affinity for phospholipid surfaces. The two major protein targets of antiphospholipid antibodies are prothrombin and β2-glycoprotein I (β2GPI). APS leads to aprothrombotic state, and it is characterized by the occurrence of arterial, venous or microvascular thrombosis or recurrent fetal loss. The diagnosis of APS is based on a set of clinical criteria and the detection of lupus anticoagulant (LA), anticardiolipin antibodies (ACA) or anti-β2GPI in plasma. Although laboratory tests are essential for APS diagnosis, these tests have limitations associated with the robustness, reproducibility and standardization. The standardization of diagnostic tests for detection of APLAs has been a challenge and a variety of results have been obtained using different commercial kits and in-house techniques. An increased sensitivity of the ELISA kits for detection of ACA effectively has contributed to APS diagnosis. However, the lack of specificity associated with a high number of false-positive results is a clinical and laboratorial challenge, since such results may lead to mistaken clinical decisions, such as prescription of oral anticoagulant, leading to the risk of hemorrhaging. Furthermore, clinicians are often unfamiliar with these tests and have difficulty interpreting them, requiring interaction between clinical and laboratory professionals in order to ensure their correct interpretation.

Antiphospholipid antibodies: evaluation of the thrombotic risk

The laboratory diagnosis of the antiphospholipid syndrome (APS) via antiphospholipid antibody (aPL) tests, including lupus anticoagulant (LAC), anti-cardiolipin (aCL), or anti-beta2 glycoprotein I (aβ2GPI) antibodies remains a challenge. Coagulation tests for LAC as well as solid phase assays for aCL and aβ2GPI have methodological shortcomings, although for LAC large progress have been made in standardization. All assays are associated with clinical APS-criteria (thrombotic and/or pregnancy complications) but with limited specificity. Besides, clinical studies demonstrating the association between the presence of aPL and thrombosis are not always well designed and result in wide ranges of odds ratio with large variation between studies. The best association between thrombotic complications and aPL is found for LAC. The association between thrombosis and aCL or aβ2GPI is at least inconsistent. The inclusion of more specific assays, such as the domain-I-β2GPI.antibodies is too premature and depends on further investigation in large clinical studies and the commercial availability. The search for new assays should proceed to identify patients with aPL with increased risk for thrombosis, preferable in large prospective studies. Meanwhile, with the current available LAC, aCL and aβ2GPI assays it is strongly recommended to make antibody profiles. Multiple positivity of tests seems clinically more relevant. The strengths and weaknesses of the current laboratory criteria for APS are discussed in view of their role in risk stratification of patients with thrombotic events.

Incidence of a first thromboembolic event in asymptomatic carriers of high-risk antiphospholipid antibody profile: a multicenter prospective study

Persistent antiphospholipid (aPL) antibodies are occasionally found in subjects without prior history of thromboembolic events (TEs), raising the dilemma of whether to initiate or not a primary thromboprophylaxis. A first TE is considered rare in aPL carriers, but previous studies did not consider the aPL profile nor was the test positivity confirmed in a reference laboratory. In this study, 104 subjects with high-risk aPL profile (positive lupus anticoagulant, anticardiolipin, and anti-β(2)-glycoprotein I antibodies, triple positivity) confirmed in a reference laboratory, were followed up for a mean of 4.5 years. There were 25 first TEs (5.3% per year): the cumulative incidence after 10 years was 37.1% (95% confidence interval [CI], 19.9%-54.3%). On multivariate analysis, male sex (hazard ratio = 4.4; 95% CI, 1.5-13.1, P = .007) and risk factors for venous thromboembolism (hazard ratio = 3.3; 95% CI, 1.3-8.5, P = .01) were independent predictors for TEs. Aspirin did not significantly affect the incidence of TE. In conclusion, the occurrence of a first TE in carriers of high-risk aPL profile is considerable; it is more frequent among male subjects and in the presence of additional risk factors for venous TE. These data can help in the decision to initiate primary thromboprophylaxis in these subjects.

Evaluation of a new set of automated chemiluminescense assays for anticardiolipin and anti-beta2-glycoprotein I antibodies in the laboratory diagnosis of the antiphospholipid syndrome

INTRODUCTION

The laboratory diagnosis of antiphospholipid syndrome (APS) requires the demonstration of antiphospholipid antibodies (aPL): lupus anticoagulant (LAC) measured through coagulation assays, anticardiolipin IgG or IgM antibodies (aCL) and/or anti-β2glycoprotein I IgG or IgM antibodies (aβ2GPI), usually detected by ELISA.

MATERIALS AND METHODS

We evaluated the diagnostic value of aCL and aβ2GPI measured by a new automated system using the chemiluminescence principle, the immunoanalyzer Zenit RA (Menarini).

RESULTS

Results of aCL and aβ2GPI were correlated with the clinical background of the patients and with results of ELISA (n=314). Correlated to the clinical background sensitivity/specificity ranged for aCL IgG between 7.5-45.2% / 54.2-98.8%, for aCL IgM 3.4-5.5% / 89.9-94%, for aβ2GPI IgG 5.5-25.3% / 75.6-100% and aβ2GPI IgM 3.4-4.8% / 89.9-92.3%, depending on the cut-off used. Sensitivity with manufacturer's cut-offs was comparable to ELISA, except for aβ2GPI IgG with a significantly lower sensitivity compared to ELISA (5.5% vs 11.6%). In the APS patient population (n=30) sensitivity of aCL IgG and aβ2GPI IgG was higher measured by ELISA compared to Zenit RA (46.7% vs 30.0%, and 46.7% vs 26.7%, respectively). Agreement between Zenit RA results and ELISA results for the four parameters was moderate (Kappa-values ranging 0.509-0.565). Sensitivity was 38.5%, 53.3%, 40% and 69.2% for aCL IgG, aCL IgM, aβ2GPI IgG and aβ2GPI IgM, respectively, applying the highest cut-off value for Zenit RA, raising towards 64.3%, 100%, 57.1%, for aCL IgG, aCL IgM, aβ2GPI IgG, respectively, in a APS patient population.

CONCLUSIONS

The new technology of chemiluminescense for measuring aPL showed good performance characteristics. Interpretation of results with a cut-off value associated with a good discrimination for disease, resulted in a lower sensitivity for the diagnosis of APS for aβ2GPI IgG measured by Zenit RA assays compared to ELISA; sensitivity for aCL IgG was comparable to ELISA. Specificity for all parameters was high and comparable for aCL and aβ2GPI.

Evaluation of three commercial ELISA kits for anticardiolipin and anti-beta2-glycoprotein I antibodies in the laboratory diagnosis of the antiphospholipid syndrome

INTRODUCTION

The laboratory criteria of the antiphospholipid syndrome (APS) include lupus anticoagulant (LAC), anticardiolipin antibodies (aCL) and anti-β2glycoprotein I antibodies (aβ2GPI) IgG or IgM.

METHODS

We evaluated three commercial ELISAs for aCL and aβ2GPI IgG and IgM: Asserachrom® ('Stago'), Bio-Rad ('BR') and the Bindazyme™ (the Binding Site, 'BS').

RESULTS

Results of all assays and of LAC were correlated with the clinical background (n=228). Sensitivity for Stago/BS/BR aCL IgG was 14%/15%/18%, for aCL IgM 1%/5%/4%, for aβ2GPI IgG 9%/10%/17% and for aβ2GPI IgM 4%/4%/3%. The specificity for Stago/BS/BR for all assays ranged from 86% to 98%. The positive predictive value (PPV) for Stago/BS/BR aCL IgG was 46%/52%/40%, for aCL IgM 8%/36%/19%, for aβ2GPI IgG 70%/67%/45% and for aβ2GPI IgM 23%/23%/20%. Combining LAC with aCL and aβ2GPI antibodies increased the sensitivity (Stago/BS/BR IgG: 26%/27%/31%, IgM: 22%/21%/26%) and PPV (Stago/BS/BR IgG: 41%/46%/36%, IgM: 34%/40%/36%). Comparing the diagnostic power of the tests, only Stago/BS aβ2GPI IgG had a Chi-square P-value lower than 0.05. The combination of LAC and IgG ELISAs of BS resulted in the lowest P-value (0.098) compared to the other combinations.

CONCLUSION

All evaluated ELISAs are a practical tool in the laboratory diagnosis of APS. The diagnostic performance shows slight differences between the ELISAs from the different manufacturers.

Standardized antigen preparation to achieve comparability of anti-beta2-glycoprotein I assays

INTRODUCTION

The Sydney classification for diagnosis of the antiphospholipid syndrome (APS) first introduced the determination of anti-beta2-glycoprotein I (anti-beta2-GPI)-antibodies in serum as laboratory criteria. In this context, widely differing results of anti-beta2-GPI assays are a concerning issue. Considerable efforts have been made to optimize ELISAs, however little attention was hitherto spent to the antigen preparation. We evaluated the influence of different beta2-GPI preparations on the ability to separate ill and healthy patients and on the comparability of anti-beta2-GPI-assays.

MATERIALS AND METHODS

Microplates were coated with various beta2-GPI preparations and anti-beta2-GPI IgG- and IgM-ELISAs were performed for 21 APS patients and 21 controls using the monoclonal calibrators HCAL and EY2C9. Subsequently, by use of a surface plasmon resonance (SPR) biosensor, affinity constants for the HCAL- and EY2C9-interaction with each beta2-GPI preparation were determined and antigen binding of sera of APS patients and controls was studied.

RESULTS

All ss2-GPI preparations showed good discrimination ability ill vs. healthy but poor inter-assay comparability in the ELISAs. Affinity constants for HCAL and EY2C9 were independent of the beta2-GPI variant (K(A) 0.105 - 0.200 and 0.449 - 1.04 x 10(10)M(-1); K(D) 50.0 - 95.5 and 9.61 - 22.3 x 10(-11)M, respectively). In the biosensor, reactivity to the different beta2-GPIs was negligible for the controls and varied considerably for patients.

CONCLUSION

Inter-assay comparability of anti-beta2-GPI ELISAs is highly dependent upon the beta2-GPI preparation. Only agreement on one common beta2-GPI preparation will improve the requested inter-assay comparability.

Challenges in the Diagnosis of the Antiphospholipid Syndrome

Background: The antiphospholipid syndrome (APS) is an important cause of acquired thromboembolic complications and pregnancy morbidity. Its diagnosis is based on clinical and laboratory criteria, defined by strict guidelines. The original clinical and laboratory criteria for the identification of APS patients were published in 1999, in the so-called Sapporo criteria. In 2006 these criteria were revised, and recently more precise guidelines for analysis of the lupus anticoagulant have been provided. However, several questions related to the diagnosis of APS remain unanswered.

Content: In addition to providing a historical perspective, this review covers several challenges in the diagnosis of APS with respect to clinical and laboratory features, while highlighting pathogenic pathways of the syndrome. We discuss ongoing dilemmas in the diagnosis of this complex disease. Although antiphospholipid antibodies are found in association with various clinical manifestations, the older established clinical criteria were not substantively altered in the 2006 update. Several laboratory tests recommended in the latest criteria, including phospholipid-dependent coagulation tests for the detection of the lupus anticoagulant and ELISAs for measuring anticardiolipin and β2-glycoprotein I antibodies, still show methodological and diagnostic shortcomings. In addition, antiphospholipid antibodies have been described against other antigens, but their clinical role remains uncertain.

Conclusions: Despite updated APS criteria, diagnosis of this syndrome remains challenging. Further research on clinically relevant antibodies and standardization of their detection are needed to improve clinical risk assessment in APS.

The association of antiphospholipid antibodies with pregnancy-related first time venous thrombosis--a population-based case-control study

In this population-based case-control study we explored the association of antiphospholipid antibodies with pregnancy-related venous thrombosis. From 1990 through 2003 615 pregnant women were identified at 18 hospitals in Norway with a diagnosis of first time VT. In 2006, 531 of 559 eligible cases and 1092 of 1229 eligible controls were invited for further investigations. The final study population comprised 313 cases and 353 controls, who completed a comprehensive questionnaire and donated a single blood sample, 3-16 years after index pregnancy. We report the results on lupus anticoagulant, anticardiolipin antibodies, and anti-ss(2) glycoprotein-1 antibodies alone, in combination, and with the contribution of the factor V Leiden and the prothrombin gene G20210A polymorphisms. Cut-off values for APAs were chosen according to current international consensus. 29 (9.3%) of the cases and 24 (6.8%) of the controls had at least one positive test for APAs (OR 1.4; 95% CI 0.8-2.5). Nine cases (2.8%) and no controls had more than one positive test (multi-positivity) for APAs. After excluding women with factor V Leiden or prothrombin polymorphisms, still 6 cases were multi-positive for APAs. We conclude that multi-positivity, but not single-positivity, for APAs was weakly associated with a history of ante- and postnatal VT.

Antiphospholipid syndrome review

The antiphospholipid syndrome (APS) is an autoimmune disorder presenting with tissue injury in various organs attributed to large or small vessel thrombosis or, in some instances, possible nonthrombotic inflammatory mechanisms, associated with in vitro evidence of antibodies to certain proteins, or proteinphospholipid complexes. Although the pathophysiology, diagnosis, and management of APS may seem clear and straightforward from a distance, closer inspection reveals a more complex, incomplete, and uncertain image. This article reviews the evolution of APS from the first description of lupus anticoagulant to the current criteria used to guide clinical research, critiques laboratory methods used to identify autoantibodies, comments on prognosis and management, and summarizes insights into the pathophysiology of this elusive disorder.