Risky business: the interpretation, use, and abuse of antiphospholipid antibody tests in clinical practice

Establishment of ELISA-comparable moderate and high thresholds for anticardiolipin and anti-β2 glycoprotein I chemiluminescent immunoassays according to the 2023 ACR/EULAR APS classification criteria and evaluation of their diagnostic performance

OBJECTIVES

Recently published 2023 ACR/EULAR APS classification criteria emphasize the importance of quantifying single-, double-, and triple-antiphospholipid antibody positivity, distinguishing between IgG and IgM isotypes, and delineating moderate/high levels of anticardiolipin (aCL) and anti-β2 glycoprotein I (anti-β2GPI) antibodies. We aimed to establish clinically important moderate/high thresholds for aCL and anti-β2GPI IgG/IgM chemiluminescent immunoassays (CLIA), in particular QUANTA Flash, comparable to our in-house ELISAs used for over two decades, and to evaluate their diagnostic performance.

METHODS

QUANTA Flash CLIA and in-house ELISAs were used to measure aCL and anti-β2GPI IgG/IgM. Moderate thresholds for QUANTA Flash CLIA were determined using a non-parametric approach, calculating a 99th percentile on serum samples from 139 blood donors, and by mirroring the diagnostic performance of in-house ELISA on 159 patient samples.

RESULTS

Thresholds for QUANTA Flash CLIA achieving diagnostic performance equivalent to in-house ELISAs were 40 CU for moderate and 80 CU for high levels for aCL and anti-β2GPI IgG and IgM. The assays showed good qualitative agreement, ranging from 76.10 to 91.19 %. When considering in-house ELISA results, 14 out of 80 (17.5 %) patients did not fulfill the new ACR/EULAR laboratory classification criteria, while 27 out of 80 (33.8 %) did not when considering QUANTA Flash CLIA results.

CONCLUSIONS

We determined moderate and high thresholds for aCL and anti-β2GPI IgG and IgM detected with QUANTA Flash CLIA, aligning with long-established in-house ELISA thresholds. These thresholds are crucial for seamlessly integrating of the new 2023 ACR/EULAR classification criteria into future observational clinical studies and trials.

Viewpoint: Lupus anticoagulant detection and interpretation in antiphospholipid syndrome

Lupus anticoagulant (LA) is a well-established risk factor for the clinical manifestations of antiphospholipid syndrome (APS). Accurate LA detection is an essential prerequisite for optimal diagnosis and management of patients with APS or aPL carriers. Variability remains a challenge in LA testing, with reliable detection influenced by multiple factors, including pre-analytical conditions, anticoagulation treatment, choice of tests and procedures performed, as well as interpretation of results, that can lead to false-positives or negatives. A standardised approach to LA testing, following current guidance, based on published data and international consensus, and with attention to detail, is required to underpin accurate detection of LA. Future work should focus on better characterisation of the nature of LA, which may ultimately lead to improved diagnosis and management of patients with APS and aPL carriers. This article reviews current practice and challenges, providing an overview on detection of LA.

16th International congress on antiphospholipid antibodies task force report on antiphospholipid syndrome laboratory diagnostics and trends

Classification criteria for antiphospholipid syndrome (APS) require IgG or IgM isotypes of the anticardiolipin (aCL) antibodies, anti-β2 glycoprotein I (anti-β2GPI) antibodies, and/or the lupus anticoagulant (LA) to satisfy the laboratory disease definition. Over the past 20 years, non-criteria antiphospholipid antibodies (aPL) directed to other proteins of the coagulation cascade (i.e. prothrombin and/or phosphatidylserine-prothrombin complex) or to some domains of β2GPI have been proposed. This task force concentrated and reviewed the literature on data including aPS/PT, antibodies to domain 4/5 of β2GPI and the newly described antibodies to protein/HLA-DR complex. In addition, we discussed testing of LA in the 'new' oral anticoagulants' era and the value of triple positivity in the risk assessment of aPL. The conclusions were presented at a special session during the 16th International Congress on aPL, Manchester, UK, September 2019.

Associations Among Antiphospholipid Antibody Types, Isotypes, and Titers: An AntiPhospholipid Syndrome Alliance for Clinical Trials and InternatiOnal Networking (APS ACTION) Study

Several antiphospholipid antibody (aPL) profiles ("triple" and lupus anticoagulant [LA] positivity) are associated with a higher risk for clinical manifestations of antiphospholipid syndrome (APS). Further risk is correlated with higher levels of anticardiolipin antibody (aCL) and anti-β2 glycoprotein-I antibody (aβ2GPI), and with aPL persistence. Given that the 3 aPL tests detect partially overlapping sets of antibodies, the primary goal of this study was to characterize the associations among aPL tests using AntiPhospholipid Syndrome Alliance for Clinical Trials and InternatiOnal Networking (APS ACTION) core laboratory data. The APS ACTION Registry includes annually followed adult patients with positive aPL based on the Revised Sapporo Classification Criteria. We analyzed baseline and prospective core laboratory data of the registry for associations among aPL tests using the Spearman rank correlation with Bonferroni-adjusted significance level for multiple comparisons. An aPL Load was calculated based on 6 tests (aCL IgG/IgM/IgA and aβ2GPI IgG/IgM/IgA); a receiver operating characteristic curve was used to evaluate the diagnostic performance of the aPL Load in predicting LA positivity. In 351 patients simultaneously tested for LA, aCL, and aβ2GPI, the frequency of moderate-to-high (≥40 U) titers of aCL and aβ2GPI IgG/IgM/IgA was higher in patients who were positive for LA vs those who were negative. An aPL Load was calculated for each patient to assess the overall aPL burden. For every 1-point increase in the aPL Load, the possibility of a positive LA test increased by 32% (odds ratio, 1.32; 95% CI, 1.2-1.5; P < .001). Based on core laboratory data from a large international registry, most aPL enzyme-linked immunosorbent assay ≥40 U and a high calculated aPL Load combining 6 aPL enzyme-linked immunosorbent assays were predictive of a positive LA. These data suggest that the combined quantitative burden of aPL may provide a mechanistic explanation of a positive LA.

Intensity of immune/clotting assays relate to multiple antiphospholipid antibody positivity in thrombotic primary antiphospholipid syndrome

The dual positivity (DP) and triple positivity (TP) concepts bypass the poor comparability of immune/clotting assay for the laboratory classification of antiphospholipid syndrome (APS). To evaluate intensity of immune/clotting assays and DP/TP through different clinical severity groups (CSG) as follows: (1) non-thrombotic asymptomatic carriers of aPL (N-THR), thrombotic primary APS (THR), deceased (D) for recurrent and fatal thrombosis. Activated partial thromboplastin time ratio (aPTTr), dilute Russell viper venom time ratio (DRVVTr), IgG/IgM anticardiolipin (aCL) and anti β-2-glycoprotein-I (aβ2GPI). Participants: 33 N-THR, 64 THR and 11 D. The frequency of DP and TP (DRVVTr or aPTTr partnered with respective IgG aCL or aβ2GPI) increased across CSG (p = 0.006 and p = 0.003); mean DRVVTr and IgG aCL/aβ2GPI were always greater in TP versus non-TP within each CSG and progressively increased across the CSG. The intensity of individual lupus anticoagulants partnered with their corresponding IgG aPL related to the frequency of multiple positivity throughout CSG suggesting that of intensity of immune/clotting assays and multiple positivity are the different faces of the same diagnostic coin in our thrombotic PAPS cohort.

Anti-phospholipid Antibodies and Smoking: An Overview

Antiphospholipid syndrome is characterized by the presence of antiphospholipid antibodies, specifically lupus anticoagulant, anticardiolipin antibodies, and anti-β2 glycoprotein-I antibodies. Antiphospholipid syndrome can occur on its own or in association with other autoimmune diseases, most commonly systemic lupus erythematosus (SLE). A connection between cigarette smoking and anti-phospholipid antibodies (aPL) was first reported in the late1980s. Systemic lupus erythematosus patients with aPL are more likely to be smokers than those without aPL. These patients have a particularly high frequency of vascular events. Recently, a potential link between periodontitis, tobacco, and aPL has been proposed. Research has also suggested that periodontitis and Porphyromonas gingivalis infection are associated with citrullination through the action of peptidylarginine deiminase. A strong correlation between smoking and the presence of citrillunated autoantibodies, which are characteristic of rheumatoid arthritis, has also been observed. While many studies have investigated possible links between infection and aPL in patients with autoimmune diseases, the association of smoking with aPL has not been systematically examined. The fact that both aPL and tobacco are risk factors for thrombosis has complicated efforts to evaluate these factors separately. Also, there has been great variability in measurement techniques, and laboratories lack routine methods for differentiating transient and persistent aPL; both of these factors can make interpretation of autoantibody results quite challenging. This review summarizes the clinical evidence supporting a posited link between aPL and smoking, both in patients with a systemic autoimmune disease and in patients with other medical conditions.

Both IgG and IgM anti-beta2 glycoprotein I antibodies assays are clinically useful to the antiphospholipid syndrome diagnosis

OBJECTIVES

The aim of our study was to evaluate the clinical values of anti-beta2 glycoprotein I antibodies (anti-beta2GPI) IgG and IgM comparing with lupus anticoagulant (LA), anticardiolipin antibodies (aCL) in the two clinical groups of antiphospholipid syndrome (APS), vascular thrombosis (VT) and pregnancy morbidity (PM).

METHODS

Eighty patients who fulfilled the APS clinical criteria, VT n = 34; PM n = 40, both VT and PM n = 6 were included. LA, aCL and three anti-beta2GPI ELISA kits were tested.

RESULTS

Sensitivities of LA, aCL and anti-beta2GPI assays were found respectively 62, 26 and 41% in VT, and 28, 28 and 30% in PM. The sensitivity for the APS diagnosis could reach to 63% using triple tests. The presence of LA (P<0·01, OR = 4·3) or anti-beta2GPI IgG alone (P<0·05, OR = 8·4) was significantly associated with VT. IgM isotype was found more frequent in PM (92%) than in VT (57%) among all positive anti-beta2GPI cases.

CONCLUSION

Both IgG and IgM anti-beta2GPI assays were useful when clinical features of APS presented, even its standardization is ongoing. A decreased by half sensitivity of LA in PM compared with that in VT underlines the importance of adding anti-beta2GPI in PM of APS, especially IgM isotype although recent review questioned its significance.

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.

Variability and diagnostic utility of antiphospholipid antibodies including lupus anticoagulants

Antiphospholipid antibodies (aPL) comprise a heterogeneous group of antibodies directed against phospholipids and/or protein-complexed phospholipids. aPL are associated with the serious autoimmune condition 'antiphosholipid (antibody) syndrome' (APS) and can be defined by either 'solid-phase' assays that identify anticardiolipin antibodies (aCL) and anti-β2-glycoprotein I antibodies (aB2GPI) or 'liquid-phase' assays that identify lupus anticoagulants (LAs). There is a lack of standardization associated with all forms of aPL testing; however, intermethod and interlaboratory variation using aCL and aB2GPI assays is generally higher than that for LA testing by dRVVT (dilute russell viper venom time) procedures. Compared with either aCL or aB2GPI, LA is also more strongly associated with clinically adverse findings of APS, including thrombosis and obstetric morbidity. This review explores the potential reasons for the above findings and concludes that ultimately a more holistic approach to aPL/APS investigations is needed.

Anticardiolipin antibody and anti-beta 2 glycoprotein I antibody assays

Antiphospholipid syndrome (APS) is an autoimmune disease and is a risk factor for a number of clinical manifestations; the classic presentations include fetal death or thrombosis (arterial or venous thromboembolism), in the presence of persistently increased titers of antiphospholipid (aPL) antibodies. The actual cause of APS is unknown but thought to be multifactorial. The disease is characterized by the presence of a heterogenous population of autoantibodies against phospholipid-binding proteins. APS presents either in isolation with no evidence of an underlying disease or in concert with an autoimmune disease such as systemic lupus erythematosus or rheumatoid arthritis. The wide diversity in clinical presentation often causes difficulty in identifying and treating patients and therefore a concise laboratory report containing interpretative comments is required to provide needed guidance to the clinician. For a diagnosis of APS to be made both clinical and laboratory classification criteria must be met. Laboratory testing to identify aPL antibodies includes lupus anticoagulant (liquid-based clotting assays) and immunological solid-phase assays (usually enzyme-linked immunosorbent assay formats) for IgG and/or IgM anticardiolipin (aCL) antibodies and anti-beta 2 glycoprotein I (β2-GPI) antibodies. Other autoantibodies, such as those directed against anionic phospholipids, can also be assayed; however they are not of clinical significance. Participation in a quality assurance program and an in-depth technical and clinical understanding of testing for aPL antibodies are required, as methods are limited by poor robustness, reproducibility, specificity, and standardization. Testing is further complicated by the lack of a "gold standard" laboratory test to diagnose or classify a patient as having APS. This chapter discusses the clinical and laboratory theoretical and technical aspects of aCL and anti-β2GPI antibody assays.

Clinical manifestations and anti-phospholipid antibodies in 712 patients with systemic lupus erythematosus: evaluation of two diagnostic assays

OBJECTIVES

To evaluate the agreement and performance of two tests for aPLs with regard to association with manifestations of the APS in patients with SLE.

METHODS

We investigated 712 SLE patients and 280 population controls. Cardiolipin and β(2) glycoprotein-I antibodies were measured with routine ELISA and a new automated method. Three positivity cut-offs (99%, 90% of controls and recommended cut-off by manufacturers) were used. Associations with previous thrombotic events, thrombocytopenia and, in a subgroup of patients, obstetric morbidity (n = 296) were evaluated. Results were compared with the LA test, performed in 380 patients.

RESULTS

Inter-test agreement was moderate (demonstrated by κ-values 0.16-0.71). Performance of the two tests was similar: at the 99th percentile cut-off, sensitivity for any thrombotic event ranged from 3.7% to 24.8%, while specificity was 84.7-97.7%. Regardless of assay, IgG isotypes were associated with venous thrombosis and ischaemic cerebrovascular disease, whereas aPLs of IgM isotype were weakly associated with ischaemic heart disease. Associations were greatly affected by aPL level. LA performed better than the specific aPL tests. LA was associated with any thrombotic event, odds ratio 5.4 (95% CI 3.1, 9.4), while the specific aPL tests ranged from non-significant to an odds ratio of 1.9 (95% CI 1.03, 3.4) using criteria cut-off. LA was also convincingly associated with other APS manifestations.

CONCLUSION

In relation to thrombotic manifestations, there was moderate agreement but no clear advantages when comparing a routine aPL ELISA with an automated method. APL isotype and titre as well as LA positivity are important for risk assessment in SLE patients.

Efficacy of the antiphospholipid score for the diagnosis of antiphospholipid syndrome and its predictive value for thrombotic events

OBJECTIVE

To define the antiphospholipid score (aPL-S) by testing multiple antiphospholipid antibodies (aPL) and to evaluate its efficacy for the diagnosis of antiphospholipid syndrome (APS) and predictive value for thrombosis.

METHODS

This study comprised 2 independent sets of patients with autoimmune diseases. In the first set of patients (n = 233), the aPL profiles were analyzed. Five clotting assays for testing lupus anticoagulant and 6 enzyme-linked immunosorbent assays (IgG/IgM anticardiolipin antibodies, IgG/IgM anti-β(2)-glycoprotein I, and IgG/IgM phosphatidylserine-dependent antiprothrombin antibodies) were included. The association of the aPL-S with a history of thrombosis/pregnancy morbidity was assessed. In the second set of patients (n = 411), the predictive value of the aPL-S for thrombosis was evaluated retrospectively. Two hundred ninety-six of these patients were followed up for >2 years. The relationship between the aPL-S and the risk of developing thrombosis was analyzed.

RESULTS

In the first set of patients, the aPL-S was higher in those with thrombosis/pregnancy morbidity than in those without manifestations of APS (P < 0.00001). For the aPL-S, the area under the receiver operating characteristic curve value was 0.752. In the second set of patients, new thromboses developed in 32 patients. The odds ratio (OR) for thrombosis in patients with an aPL-S of ≥30 was 5.27 (95% confidence interval [95% CI] 2.32-11.95, P < 0.0001). By multivariate analysis, an aPL-S of ≥30 appeared to be an independent risk factor for thrombosis (hazard ratio 3.144 [95% CI 1.383-7.150], P = 0.006).

CONCLUSION

The aPL-S is a useful quantitative index for diagnosing APS and may be a predictive marker for thrombosis in autoimmune diseases.

Predominant prevalence of arterial thrombosis in Japanese patients with antiphospholipid syndrome

Objective: To study the clinical and immunological manifestations of antiphospholipid syndrome (APS) in the Japanese population by a single-centre registration. Methods: In this retrospective cohort study, 141 consecutive patients with APS, fulfilling the Sydney revised Sapporo criteria for definite APS, who visited our autoimmune clinic from 1988 to 2010, were recruited and followed up. All the patients were interviewed and underwent a general physical examination by qualified rheumatologists on the day of blood sampling. Results: The population comprised 119 woman and 22 men with a mean age at diagnosis of 44 years (range 9–79 years). Seventy patients (49.6%) had primary APS, and 71 (50.4%) had systemic lupus erythematosus. The prevalence of thrombosis was 85.8 per cent, arterial thrombosis was found in 93 patients (66.0%) and venous thrombosis was found in 46 patients (32.6%). The most common thrombosis was cerebral infarction [86/141 (61.0%)] followed by deep vein thrombosis [33/141 (23.4%)]. Among 70 pregnant women, 45 (64.3%) had obstetric complications. Lupus anticoagulant was detected in 116 patients (82.3%), anticardiolipin antibodies in 83 (58.9%), anti-β2 glycoprotein I antibodies in 73 (51.8%) and phosphatidylserine-dependent antiprothrombin antibodies in 98 (69.5%). Conclusion: High prevalence of arterial thrombosis was noted in Japanese patients with APS. The profile of heterogeneous and complex clinical manifestations was substantiated in Japanese patients with APS.

Cardiovascular event in systemic lupus erythematosus in northern Sweden: incidence and predictors in a 7-year follow-up study

INTRODUCTION

An increased rate of cardiovascular disease (CVD) has been suggested in patients with systemic lupus erythematosus (SLE). The risk for myocardial infarction (MI), coronary artery disease and stroke has been reported as particularly prevalent in younger females compared with the reference population. This study was performed to analyse the standard incidence ratio (SIR) of and predictors for cardiovascular events (CVEs) in patients with SLE from northern Sweden, with a fairly homogenous population.

METHODS

In 2000 all prevalent patients with SLE (≥4 American College of Rheumatology [ACR] criteria; n = 277) from the four northern-most counties of Sweden were assessed with clinical and laboratory analyses. Seven years follow-up data concerning MI and stroke were extracted from the national registers of hospitalization and death in Sweden. The incidence ratio among the patients was compared with that for the general population from the same catchment area using data from the same register and Statistics Sweden. To identify time to event and CVE predictors, two matched controls for each patient were used and disease related variables as CVD predictors.

RESULTS

The SIR for a CVE was 1.27 (95% CI 0.82-1.87) and for females separately aged 40-49 years was 8.00 (95% CI 1.65-23.38). The overall SIR for MI was 2.31 (95% CI 1.34-3.7), for females overall was 1.75 (95% CI 0.84-3.22) and for females aged between 40 and 49 years was 8.7 (95% CI 1.1-31.4). The time to an event was significantly shorter among SLE patients (p < 0.001) and was predicted by hypertension adjusted for smoking and disease. High SLEDAI and anti-cardiolipin IgG antibodies predicted an event in Cox proportional hazards regression models adjusted for age and previous MI. Diabetes, smoking ever and sex did not affect the prediction models.

CONCLUSION

The risk of a CVE, or MI, was eight- or nine-fold greater among middle-aged female SLE patients. Time to event was significantly shorter and CVE was associated with SLE-related factors including hypertension and age.

Evidence-based recommendations for the prevention and long-term management of thrombosis in antiphospholipid antibody-positive patients: report of a task force at the 13th International Congress on antiphospholipid antibodies

The antiphospholipid syndrome (APS) is defined by the presence of thrombosis and/or pregnancy morbidity in combination with the persistent presence of circulating antiphospholipid antibodies: lupus anticoagulant, anticardiolipin antibodies and/or anti-β2-glycoprotein I antibodies in medium to high titers. The management of thrombosis in patients with APS is a subject of controversy. This set of recommendations is the result of an effort to produce guidelines for therapy within a group of specialist physicians in Cardiology, Neurology, Hematology, Rheumatology and Internal Medicine, with a clinical and research focus on APS.

Antiphospholipid Syndrome Clinical Research Task Force report

The Antiphospholipid Syndrome (APS) Clinical Research Task Force (CRTF) was one of six Task Forces developed by the 13(th) International Congress on Antiphospholipid Antibodies (aPL) organization committee with the purpose of: a) evaluating the limitations of APS clinical research and developing guidelines for researchers to help improve the quality of APS research; and b) prioritizing the ideas for a well-designed multicenter clinical trial and discussing the pragmatics of getting such a trial done. Following a systematic working algorithm, the Task Force identified five major issues that impede APS clinical research and the ability to develop evidence-based recommendations for the management of aPL-positive patients: (1) aPL detection has been based on partially or non-standardized tests, and clinical (and basic) APS research studies have included patients with heterogeneous aPL profiles with different clinical event risks; (2) clinical (and basic) APS research studies have included a heterogeneous group of patients with different aPL-related manifestations (some controversial); (3) thrombosis and/or pregnancy risk stratification and quantification are rarely incorporated in APS clinical research; (4) most APS clinical studies include patients with single positive aPL results and/or low-titer aPL ELISA results; furthermore, study designs are mostly retrospective and not population based, with limited number of prospective and/or controlled population studies; and (5) lack of the understanding the particular mechanisms of aPL-mediated clinical events limits the optimal clinical study design. The Task Force recommended that there is an urgent need for a truly international collaborative approach to design and conduct well-designed prospective large-scale multi-center clinical trials of patients with persistent and clinically significant aPL profiles. An international collaborative meeting to formulate a good research question using 'FINER' (Feasible; Interesting; Novel; Ethical; and Relevant) criteria took place in November 2010.