Assessing the usefulness of anticardiolipin antibody assays: a cautious approach is suggested by high variation and limited consensus in multilaboratory testing

Evolution of Hemostasis Testing: A Personal Reflection Covering over 40 Years of History

There is no certainty in change, other than change is certain. As Seminars in Thrombosis and Hemostasis celebrates 50 years of publication, I felt it appropriate to reflect on my own 40-year plus scientific career. My career in the thrombosis and hemostasis field did not start until 1987, but the subsequent 35 years reflected a period of significant change in associated disease diagnostics. I started in the Westmead Hospital "coagulation laboratory" when staff were still performing manual clotting tests, using stopwatches, pipettes, test tubes, and a water bath, which we transported to the hospital outpatient department to run our weekly warfarin clinic. Several hemostasis instruments have come and gone, including the Coag-A-Mate X2, the ACL-300R, the MDA-180, the BCS XP, and several StaR Evolution analyzers. Some instruments remain, including the PFA-100, PFA-200, the AggRAM, the CS-5100, an AcuStar, a Hydrasys gel system, and two ACL-TOP 750s. We still have a water bath, but this is primarily used to defrost frozen samples, and manual clotting tests are only used to teach visiting medical students. We have migrated across several methodologies in the 45-year history of the local laboratory. Laurel gel rockets, used for several assays in the 1980s, were replaced with enzyme-linked immunosorbent assay assays and most assays were eventually placed on automated instruments. Radio-isotopic assays, used in the 1980s, were replaced by an alternate safer method or else abandoned. Test numbers have increased markedly over time. The approximately 31,000 hemostasis assays performed at the Westmead-based laboratory in 1983 had become approximately 200,000 in 2022, a sixfold increase. Some 90,000 prothrombin times and activated partial thromboplastic times are now performed at this laboratory per year. Thrombophilia assays were added to the test repertoires over time, as were the tests to measure several anticoagulant drugs, most recently the direct oral anticoagulants. I hope my personal history, reflecting on the changes in hemostasis testing over my career to date in the field, is found to be of interest to the readership, and I hope they forgive any inaccuracies I have introduced in this reflection of the past.

Antiphospholipid syndrome and recurrent miscarriage: A systematic review and meta-analysis

Antiphospholipid syndrome (APS) is an autoimmune condition that is associated with thrombosis and morbidity in pregnancy. The exact mechanisms by which these associations occur appear to be heterogeneous and are not yet well understood. The aim of this study was to identify and analyze publications in recent years to better understand the diagnosis and its contribution to monitoring APS among women with recurrent miscarriage (RM). This systematic review and meta-analysis was conducted using the PubMed and Web of Knowledge databases, with articles published between 2010 and 2014, according to the PRISMA statement. Of the 85 identified studies, nine were selected. Most of the studies reported an association between recurrent miscarriage and specific antiphospholipid antibodies, as anticardiolipin antibodies (aCL), lupus anticoagulant (LA), anti-β2-glycoprotein I antibodies (aβ2GPI) and antiphosphatidylserine (aPS), which showed a relationship with RM. The main result of the meta-analysis revealed association between antiphospholipid antibodies (aPLs) and/or APS compared to the patients with RM (OR: 0.279; 95% CI: 0.212-0.366) and APS cases compared to the patients with RM (OR: 0.083; 95% CI: 0.036-0.189). High heterogeneity among these studies (I²=100.0%, p <0.001) was observed. In addition, there was no significant publication bias across studies according to Begg's test (p=0.230), although Egger's test (p=0.037) suggests significant publication bias. The funnel plot was slightly asymmetrical. Systematic review and meta-analysis demonstrated a positive association between antiphospholipid antibodies and/or antiphospholipid syndrome in patients with recurrent miscarriage.

Variability in Anticardiolipin Antibody Detection: Role of Nonspecific IgG Binding and Different Microtiter Plates

There are many studies that are available on the Internet that attempt to standardize the assay for anticardiolipin antibody evaluation because of the variability of results. The aim of this study was to evaluate simultaneously the role of different microplates and the importance of sample nonspecific binding in determining different results in anticardiolipin antibody detection. Sera from 8 patients with raised levels of IgG anticardiolipin antibodies and 10 control sera were assayed by enzyme-linked immunosorbent assay in the presence (specific binding) or in the absence of cardiolipin (sample blank) with four different microplates, that is, NUNC PolySorp, FALCON ProBIND, Greiner 655061 (high binding), and Greiner 655001 (medium binding). Results were expressed as optical densities or net-optical densities (following sample blank subtraction) as well as international IgG anticardiolipin units (GPL) or net-GPL. A wide interplate variability of optical densities was found. When results were expressed as GPL, significant differences were only found between Greiner 655061, FALCON ProBIND, and NUNC PolySorp ( P < .05 and P < .001, respectively) whereas differences were not statistically significant if interplate variability was analyzed as net-GPL. Results expressed as categorical variables (ie, positive/negative, according to a GPL cut-off and net-GPL cut-off, obtained with sera from 100 apparently healthy blood donors) showed a good or excellent Cohen's κ coefficient of concordance among plates when positivity was evaluated on net-GPL. Our data strongly suggest that quantification and subtraction of sample blank may improve both interlaboratory agreement and reliability of anticardiolipin assay and minimize false-positive results.

Low level autoantibodies can be frequently detected in the general Australian population

The aim of this study was to determine the prevalence and type of autoantibodies in a general Australian population cohort. Samples collected from 198 individuals included in a cross sectional Busselton Health Study were tested using autoantibody assays routinely performed at Clinical Immunology, PathWest Laboratory Medicine, Western Australia. At least one autoantibody was detected in 51.5% of individuals (males = 45.1%, females = 58.3%). The most frequently detected serum autoantibodies were anti-beta-2-glycoprotein I (12.1%) followed by anti-smooth muscle (11.6%) and anti-thyroid peroxidase (8.6%). Vasculitis associated anti-neutrophil cytoplasmic antibodies were present in 5.1%, while anti-nuclear antibodies were detected in 8.6% of individuals. Notably, 65% of positive results were detected at low levels with the exception of anti-myeloperoxidase and anti-beta 2 glycoprotein I IgG antibodies. Autoantibodies are commonly detected at low levels in a predominantly Australian or European population cohort. No large Australian study has yet provided these data for contemporary routine tests. This paper gives important information on the background frequency of autoantibodies in the general population. Due to the nature of this study we are unaware of whether these individuals have subsequently developed an autoimmune disease, however this was not clinically diagnosed at the time of sample collection.

A Clinical Approach for Defining the Threshold between Low and Medium Anti-Cardiolipin Antibody Levels for QUANTA Flash Assays

The threshold between low and medium antibody levels for anticardiolipin (aCL) and anti-β2 glycoprotein I antibodies (aβ2GPI) for the diagnosis of antiphospholipid syndrome (APS) remains a matter of discussion. Our goal was to create a protocol for determining the low/medium antibody cut-off for aCL antibody methods based on a clinical approach, and utilize it to establish the clinically-relevant low/medium threshold for QUANTA Flash aCL chemiluminescent immunoassay (CIA) results. The study included 288 samples from patients with primary APS (n = 70), secondary APS (n = 42), suspected APS (n = 36), systemic lupus erythematosus (SLE) without APS (n = 96) and other connective tissue diseases (n = 44). All samples were tested for IgG and IgM aCL antibodies with QUANTA Flash CIA, along with traditional enzyme-linked immunosorbent assays (ELISAs) (QUANTA Lite). The assay specific low/medium threshold for QUANTA Flash aCL IgG and IgM assays (i.e., the equivalent of 40 GPL and MPL units) was established as 95 and 31 chemiluminescent units (CU), respectively, based on clinical performance and comparison to QUANTA Lite ELISAs. Agreement between CIA and ELISA assay results improved substantially when the platform-specific low/medium antibody threshold was used, as compared to agreement obtained on results generated with the assay cutoff: Cohen's kappa increased from 0.85 to 0.91 for IgG aCL, and from 0.59 to 0.75 for IgM aCL results. This study describes a clinical approach for establishing the low/medium antibody threshold for aPL antibody assays, and successfully employs it to define 95 and 31 CU, respectively, as the low/medium cut point for QUANTA Flash aCL IgG and IgM results. This study can serve as a model for labs wishing to establish the appropriate low/medium aPL antibody threshold when implementing new aPL antibody assays.

β2GP1, Anti-β2GP1 Antibodies and Platelets: Key Players in the Antiphospholipid Syndrome

Anti-beta 2 glycoprotein 1 (anti-β2GP1) antibodies are commonly found in patients with autoimmune diseases such as the antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE). Their presence is highly associated with increased risk of vascular thrombosis and/or recurrent pregnancy-related complications. Although they are a subtype of anti-phospholipid (APL) antibody, anti-β2GP1 antibodies form complexes with β2GP1 before binding to different receptors associated with anionic phospholipids on structures such as platelets and endothelial cells. β2GP1 consists of five short consensus repeat termed "sushi" domains. It has three interchangeable conformations with a cryptic epitope at domain 1 within the molecule. Anti-β2GP1 antibodies against this cryptic epitope are referred to as 'type A' antibodies, and have been suggested to be more strongly associated with both vascular and obstetric complications. In contrast, 'type B' antibodies, directed against other domains of β2GP1, are more likely to be benign antibodies found in asymptomatic patients and healthy individuals. Although the interactions between anti-β2GP1 antibodies, β2GP1, and platelets have been investigated, the actual targeted metabolic pathway(s) and/or receptor(s) involved remain to be clearly elucidated. This review will discuss the current understanding of the interaction between anti-β2GP1 antibodies and β2GP1, with platelet receptors and associated signalling pathways.

Clinical utility of automated chemiluminescent antiphospholipid antibody assay

BACKGROUND

The threshold for clinically relevant levels of antiphospholipid (aPL) antibodies for the diagnosis of antiphospholipid syndrome (APS) remains a matter of debate. As new technologies for antibody detection are introduced, their performance characteristics must be clearly understood and compared to traditional assays.

OBJECTIVES

To assess the analytical performance and clinical utility of fully automated anticardiolipin (aCL) and anti-β2 glycoprotein I (aβ2GPI) chemiluminescent immunoassays (CIA) in comparison to the traditional ELISA tests.

PATIENTS/METHODS

Samples from 220 autoimmune patients were studied (primary APS - 74; secondary APS - 47, systemic lupus erythematosus (SLE) without APS - 99). All samples were tested for IgG and IgM aCL and β2GPI antibodies using both CIA and ELISA, and for lupus anticoagulant (LAC).

RESULTS

Good qualitative agreement and quantitative correlation were found between methods in regard to individual antibodies and their categories (profiles). All assays showed good clinical performance in APS, and strong correlation with APS-related clinical symptoms. Importance of determining individual laboratory 99 percentile values for a healthy population as normal cut-off values was shown. Additionally, based on a clinical approach, this study has established the low/medium threshold for QUANTA Flash aCL IgG and IgM assays.

CONCLUSIONS

This study showed good clinical performance and strong correlation of the new automated CIA aPL assays with APS clinical symptoms. It also enabled us to determine the corresponding low/medium antibody threshold for the aCL antibody methods with different unit types.

The chequered history of the antiphospholipid syndrome

Consideration of the chronology of advances in medical knowledge can provide useful insights into the pathogenesis, diagnosis and treatment of diseases. The antiphospholipid syndrome is an enigmatic disorder and this is reinforced by the misleading associated terminology, the adoption of which results directly from early discoveries relating to the condition. Thus the target antigen of the causative autoantibodies in antiphospholipid syndrome does not reside on phospholipid, and the frequently associated lupus anticoagulant is not restricted to subjects with systemic lupus erythematosus and, paradoxically, despite causing prolongation of clotting times in vitro it is associated with a pronounced tendency to thrombosis. Recognition of the antiphospholipid syndrome has its origins in the identification of subjects with so-called biological false-positive serological reactions for syphilis in the middle years of the last century. Since that time there have been considerable advances in our understanding of the pathogenesis of the disease and the clinical manifestations and associations, improved diagnostic accuracy and an evolving evidence base for optimal therapy. However many gaps in our knowledge remain.

A new Eu(3+)-labeled method for anticardiolipin antibody IgM

BACKGROUND

The anticardiolipin antibodies (aCL) test has become a laboratory standard for the clinical diagnosis of antiphospholipid syndrome (APS). To better the quantitative detection of aCL-IgM so as to classify patients correctly and timely as APS positive, we established herein a new immunoassay based on a time-resolved fluoroimmunoassay (TRFIA).

METHODS

The complex of cardiolipin plus bovine anti-β2 glycoprotein-I was used as antigen fixed on microtiter plates to detect serum aCL-IgM, and Eu(3+) -labeled rabbit antihuman IgM was used as conjugate. The precision, sensitivity, specificity, coefficient of recovery, and stability of the assay were evaluated, and comparison with the traditional, classical enzyme-linked immunosorbent assay (ELISA) was also made.

RESULTS

The detection limit of the aCL-IgM TRFIA kit we established was 0.1 MPL U/ml, with a wider detectable range than commercial ELISA ones when a strong-positive specimen was diluted from 2,630.9 to 0.08 MPL U/ml. There was a good liner range within 0.16 to 2,630.9 MPL U/ml, whereas it was within 5.14 to 328.86 MPL U/ml when using three commercial ELISA ones. The average intra- and interassay variability was 3.19 and 3.70%, respectively. The mean recovery rate was 101.95%. The clinical diagnostic specificity was 98%. Additionally, the established assay kit presented good characteristics of stability and correlated well with the ELISA, and the correlation coefficient was 0.955.

CONCLUSION

The aCL-IgM TRFIA provides an approach to a more sensitive and reliable diagnosis of APS. Further validation of its use is required.

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.

Diagnosis of antiphospholipid syndrome in routine clinical practice

The updated international consensus criteria for definite antiphospholipid syndrome (APS) are useful for scientific clinical studies. However, there remains a need for diagnostic criteria for routine clinical use. We audited the results of routine antiphospholipid antibodies (aPLs) in a cohort of 193 consecutive patients with aPL positivity-based testing for lupus anticoagulant (LA), IgG and IgM anticardiolipin (aCL) and anti-ß₂glycoprotein-1 antibodies (aß₂GPI). Medium/high-titre aCL/aβ₂GPI was defined as >99th percentile. Low-titre aCL/aβ₂GPI positivity (>95^th< 99^th percentile) was considered positive for obstetric but not for thrombotic APS. One hundred of the 145 patients fulfilled both clinical and laboratory criteria for definite APS. Twenty-six women with purely obstetric APS had persistent low-titre aCL and/or aβ₂GPI. With the inclusion of these patients, 126 of the 145 patients were considered to have APS. Sixty-seven out of 126 patients were LA-negative, of whom 12 had aCL only, 37 had aβ₂GPI only and 18 positive were for both. The omission of aCL or aβ₂GPI testing from investigation of APS would have led to a failure to diagnose APS in 9.5% and 29.4% of patients, respectively. Our data suggest that LA, aCL and aβ₂GPI testing are all required for the accurate diagnosis of APS and that low-titre antibodies should be included in the diagnosis of obstetric APS.

Detection of anticardiolipin antibody IgG by time-resolved fluoroimmunoassay

In an effort to improve the quantitative detection of anticardiolipin antibodies (aCL) IgG so as to classify patients correctly as antiphospholipid syndrome (APS) positive, we developed a new immunoassay based on a sandwich time-resolved fluoroimmunoassay (TRFIA) using the complex of cardiolipin plus bovine β(2)GPI as antigen and Eu(3+)-labeled rabbit antihuman IgG as conjugate. The precision, sensitivity, specificity, and stability of the assay were evaluated, and comparison with the classical ELISA was also made. The aCL IgG TRFIA kit we established had a wider detectable range than three commercial ELISA ones from different manufacturers when a specimen was diluted, with strong positive result from 1:12.5 to 1:204,800. The average intra-assay and inter-assay CVs detected by the aCL IgG TRFIA was 3.14 and 3.70 %, respectively. The sensitivity was 0.1 GPL U/ml, and the clinical diagnostic specificity was 98 %. The established assay kit also behaved better in stability than the commercial ELISA ones. Additionally, the immunoassay we established correlated well with the ELISA, and the correlation coefficient was 0.975. We thus conclude that the TRFIA we developed for aCL IgG detection gives promise to a more sensitive and reliable diagnosis of APS and has potential value for large-scale screening programs.

Recent developments in our understanding of the antiphospholipid syndrome

The antiphospholipid syndrome is an autoimmune disease that manifests clinically as recurrent thrombotic complications or foetal losses and serologically with elevated levels of antiphospholipid antibodies in the plasmas of these patients. The term 'antiphospholipid syndrome' is confusing, because the auto-antibodies are not directed against phospholipids but towards a plasma protein, β(2) -glycoprotein I. For many years, the reason why auto-antibodies against β(2) -glycoprotein I were pro-thrombotic was unclear, because β(2) -glycoprotein I seems to be an obsolete protein in our circulation. Human and mice deficient in this protein do not express a clear phenotype. Recent studies on the structure and function of β(2) -glycoprotein I have provided novel insights into the importance of this protein in physiology and its role in the pathology of the antiphospholipid syndrome.

Antiphospholipid syndrome: laboratory detection, mechanisms of action and treatment

The antiphospholipid syndrome (APS) identifies a condition at increased risk of vascular occlusion and/or pregnancy complications. Patients are defined as having APS if they have at least one clinical (vascular occlusion and/or pregnancy complications) and one laboratory criterion at the same time. The laboratory criteria that define APS are repeated positivity (confirmed 12 weeks apart) for lupus anticoagulants and/or antibodies targeted against cardiolipin or β(2) -glycoprotein I immobilized on solid surfaces. Over the years, APS has attracted the interest of many medical specialties. The aim of this review is to provide an update on (i) the laboratory criteria that determine the presence of APS, (ii) how the antibodies increase the risk of vascular occlusion and foetal loss and (iii) the treatment of the related clinical events.

Primary antiphospholipid syndrome presenting as renal vein thrombosis and membranous nephropathy

Antiphospholipid syndrome is a multisystem auto-immune disorder characterized by thrombotic events and the presence of circulating antiphospholipid antibodies. Large vessel involvement in the form of thrombosis/stenosis and thrombotic microangiopathy is a commonly described renal finding. However, non-thrombotic glomerulopathies are increasingly being recognized in patients with antiphospholipid syndrome. We report a rare occurrence of both renal vein thrombosis and membranous nephropathy in a previously healthy adolescent male. Investigations revealed persistently positive antiphospholipid antibodies in the absence of an underlying systemic autoimmune disorder or malignancy. Our patient responded favourably to anti-proteinuric therapy and anticoagulation with complete resolution of proteinuria and a nearly occlusive thrombus.

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.

‘Criteria’ aPL tests: Report of a Task Force and preconference workshop at the 13th International Congress on Antiphospholipid Antibodies, Galveston, Texas, April 2010

Current classification criteria for definite antiphospholipid syndrome (APS) mandate the use of one or more of three positive ‘standardized’ laboratory assays to detect antiphospholipid antibodies (aPL) (viz: anticardiolipin [aCL] IgG and IgM; anti-β2glycoprotein I [anti-β2GPI] antibodies IgG and IgM; and/or a lupus anticoagulant [LAC]), when at least one of the two major clinical manifestations (thrombosis or pregnancy losses) are present. Although, efforts of standardization for these ‘criteria’ aPL tests have been conducted over the last 27 years, reports of inconsistencies, inter-assay and inter-laboratory variation in the results of aCL, LAC, and anti-β2GPI, and problems with the interpretation and the clinical value of the tests still exist, which affect the consistency of the diagnosis of APS. A Task Force of scientists and pioneers in the field from different countries, subdivided in three working groups, discussed and analyzed critical questions related to ‘criteria’ aPL tests in an evidence-based manner, during the 13th International Congress on Antiphospholipid Antibodies (APLA 2010, April 13–16, 2010, Galveston, TX). These included: review of the standardization and the need for international consensus protocol for aCL and anti-β2GPI tests; the use of monoclonal and/or polyclonal standards in the calibration curve of those tests; and the need for establishment of international units of measurement for anti-β2GPI tests. The group also reviewed the recently updated guidelines for LAC testing, and analyzed and discussed the possibility of stratification of ‘criteria’ aPL tests as risk factors for APS, as well as the clinical value of single positive vs. multiple aPL positivity. The group members presented, discussed, analyzed data, updated and re-defined those critical questions at a preconference workshop that was open to congress attendees. This report summarizes the findings, conclusions, and recommendations of this Task Force.

Laboratory testing for the antiphospholipid syndrome: making sense of antiphospholipid antibody assays

The antiphospholipid syndrome (APS) is an autoimmune condition characterised by a wide range of clinical features (primarily thrombosis and/or obstetric related), associated with the presence of antiphospholipid antibodies (aPL) as detected by a diverse range of laboratory tests. APS remains a significant diagnostic challenge for clinicians across a wide range of specialities, largely due to issues related to laboratory testing as well as the expanding range of reported clinical manifestations of APS. The laboratory issues include limitations in detailed knowledge by both clinical and laboratory personnel regarding the 'complete' range of available aPL tests, as well as ongoing problems with assay reproducibility and standardisation. aPL are identified using diverse laboratory procedures based on one of two distinct test processes, namely solid phase and liquid phase assays. The former includes anticardiolipin antibodies (aCL) and anti-β(2)-glycoprotein I antibodies (aβ(2)GPI). The latter are centred on clot-based tests that are used to identify the so-called lupus anticoagulant (LA). This article will discuss: (i) issues related to laboratory testing for APS in terms of the currently available solid-phase and liquid-phase assays, and identifiable biases resulting from these tests usually being performed in different laboratories; (ii) current problems with calibration, standardisation and reproducibility of these assays; (iii) pre-analytical, analytical and post-analytical considerations and ongoing initiatives for improvement; (iv) issues related to potential combinations/panels of available aPL tests; and (v) the entities of seropositive APS, seronegative APS and non-APS aPL-positivity. In doing so, this review will hopefully help bridge the two disciplines of haematology and immunology ('representing' liquid-phase and solid-phase aPL testing, respectively), by improving the understanding of those working in each of these disciplines of the merits and limitations of the assays performed in the other discipline, and encouraging inter-discipline cooperation in the reporting of aPL test results.

Antiphospholipid antibodies--we are not quite there yet

The diagnosis of antiphospholipid syndrome is predominantly made in the laboratory and depends on the persistent presence of antiphospholipid antibodies in individuals with thrombosis or pregnancy morbidity. Correct diagnosis of the syndrome is imperative to prevent unnecessary long secondary thromboprophylaxis. Three antiphospholipid antibody subtypes are included in the classification criteria of the antiphospholipid syndrome: lupus anticoagulants, anticardiolipin antibodies and anti-β2-glycoprotein I antibodies. Only lupus anticoagulants are undisputedly associated with thrombosis, which is why the serological criteria of the antiphospholipid syndrome are under debate. All of the assays used to detect antiphospholipid antibodies are in need of better standardization, although progress has been made in the detection of lupus anticoagulants. The inconsistent association between both anticardiolipin and anti-β2-glycoprotein I antibodies and thrombosis is a cause for alarm. We are in need of better assays to detect those individuals at risk for thrombosis and population-based prospective studies to provide us with accurate risk assessments.

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.

The antiphospholipid syndrome: a large elephant with many parts or an elusive chameleon disguised by many colours?

The antiphospholipid syndrome (APS) is characterized by a range of clinical features (primarily thrombosis and/or obstetric-related), together with the presence of antiphospholipid antibody (aPL) as detected by a diverse range of laboratory tests. APS remains a significant diagnostic and management challenge for clinicians across a wide range of specialties, some 30 years after APS was first described as a discrete clinical entity. This is due to ongoing issues regarding nomenclature, the diagnosis of APS in individual patients, the expanding range of recognized clinical manifestations and of APS-related laboratory tests, and management issues in particular APS patient subgroups (including obstetric and catastrophic APS). In addition to the presence of appropriate clinical features, the diagnosis of APS fundamentally requires the finding of positive aPL test result(s), which is hampered by ongoing problems with assay reproducibility and standardization. This review focuses on ongoing dilemmas and issues related to clinical and laboratory aspects of APS including: (1) diagnostic challenges posed by the protean clinical manifestations of APS; (2) current nomenclature and recent proposals for revision of the 2006 international classification criteria; (3) an overview of some key issues related to aPL testing; (4) potential pitfalls of applying the APS classification criteria as diagnostic criteria; and (5) the controversial subgroups of seronegative APS and non-APS aPL positivity.

Analytical and clinical performance of a new, automated assay panel for the diagnosis of antiphospholipid syndrome

SUMMARY BACKGROUND

Anticardiolipin (aCL) and anti-beta(2)glycoprotein I (abeta(2)GPI) antibodies are part of the criteria for antiphospholipid syndrome (APS). Therefore they are widely measured and about 30 commercial kits are available.

OBJECTIVES

To investigate the analytical and clinical performances of four fully automated, chemiluminescent assays: HemosIL AcuStar aCL IgG, HemosIL AcuStar aCL IgM, HemosIL AcuStar abeta(2)GPI IgG, and HemosIL AcuStar abeta(2)GPI IgM.

METHODS

Cut-off values were assessed by testing 250 blood donors. Total coefficients of variation (CV) were determined with six plasma pools and two controls ranging from 4.3 to 2694 U mL(-1) depending on the assay. Samples from 218 well-characterized patients and 103 controls were measured in three laboratories to determine inter-laboratory variation. The results of the 321 samples were compared with three commercial assays (REAADS, INOVA and VARELISA).

RESULTS

Cut-off values were assigned to 20 arbitrary units for all the tests. Total CV ranged from 4.3 to 11.2%. No interference of hemoglobin, bilirubin, triglycerides, heparins and rheumatoid factor was observed. Inter-laboratory variability was low and no sample changed status. Overall status agreement between HemosIL assays and the comparator kits ranged from 82 to 96%. Sensitivity, specificity, agreement when predicting APS and the odds ratios when predicting a thrombotic or obstetric event gave comparable results between HemosIL AcuStar and the three other assays.

CONCLUSIONS

Our study demonstrates that the fully automated HemosIL AcuStar aPL assay panel showed similar performances to the three commercial ELISAs commonly used by various laboratories to detect antiphospholipid antibodies.

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.

Development of recombinant human IgA for anticardiolipin antibodies assay standardization

Controls and calibrators in autoimmune assays are typically developed from patient sera. However, the use of sera is accompanied by a number of disadvantages, such as lack of monospecificity, lack of assay comparability, and supply limitations. Ideally, the control reagent would be an antigen-specific human monoclonal antibody preparation that is defined and pure, easy to produce without any supply limitations, and of defined isotype (IgG, IgM, or IgA). The generation of antigen-specific human monoclonal antibodies has been complicated, but recent advances in development of fully human antibodies by means of in vitro antibody gene library selection has opened a way for the isolation of human antibodies to virtually any antigen, including self-antigens. Such antibodies can be converted to any isotype by gene cloning. Here we developed a set of human monoclonal IgA antibodies specific for the cardiolipin-beta2-glycoprotein 1 complex, using the HuCAL technology. We evaluated the IgA variants of those antibodies for their use as standards in IgA anticardiolipin antibody assays and compared these reagents with serum controls. Such recombinant antibodies may ultimately replace patient sera as assay control and calibration reagents.

Clinical relevance of multiple antibody specificity testing in anti-phospholipid syndrome and recurrent pregnancy loss

We wanted to evaluate whether testing for anti-phosholipid antibodies other than anti-cardiolipin (aCL) and anti-beta-2 glycoprotein I (abeta2GPI) immunoglobulin (Ig)G and IgM identifies patients with recurrent pregnancy loss (RPL) who may be positive for anti-phospholipid syndrome (APS). In a cross-sectional study comprising 62 patients with APS, 66 women with RPL, 50 healthy blood donors and 24 women with a history of successful pregnancies, we tested IgM and IgG antibodies to phosphatidic acid, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl glycerol, phosphatidyl inositol and phosphatidyl serine with and without beta-2 glycoprotein I (beta2GPI) from a single manufacturer as well as aCL and abeta2GPI antibodies. Diagnostic accuracies of individual and combined anti-phospholipid (aPL) assays were assessed by computing sensitivities, specificities, positive predictive values and negative predictive values together with their 95% confidence intervals. There was a general trend for increased sensitivities in the presence of beta2GPI co-factor with significant effect for certain specificities. The overall combined sensitivity of the non-recommended aPL assays was not significantly higher than that of the aCL and aB2GPI tests. Multiple aPL specificities in RPL group is not significantly different from controls and therefore of no clinical significance.

A protocol for determination of anticardiolipin antibodies by ELISA

The anticardiolipin (aCL) test has been widely used by physicians since the mid-1980s for diagnosing patients with antiphospholipid syndrome (APS). Establishment of this diagnosis has enabled effective management of patients with recurrent thrombosis or recurrent pregnancy losses. The test was first established in 1983 as a radioimmunoassay and soon thereafter converted into ELISA. There have been numerous efforts to standardize the aCL test, but precise reproducible measurement of aCL levels is difficult and the use of semiquantitative measurements (high, medium and low) is recommended as this is probably sufficient for clinical diagnosis. Using validated ELISAs for measuring aCL Abs offers greater reproducibility, would reduce interlaboratory variations and limit discrepancies in results between different laboratories. This article details a procedure that takes approximately 2 h and summarizes the information available on the aCL ELISA test.

Antiphospholipid antibodies: laboratory and pathogenetic aspects

Antiphospholipid antibodies (aPL) constitute a heterogeneous group of autoantibodies that share the ability to bind phospholipids (PL) alone, protein-PL complexes, or PL-binding proteins. They have been detected in isolation, in association with autoimmune diseases such as systemic lupus erythematosus (SLE), and during the course of different infections. aPL have been associated with an array of clinical manifestations in virtually every organ, although deep vein and arterial thrombosis as well as pregnancy morbidity are predominant. The co-occurrence of these clinical findings with aPL constitutes the so-called antiphospholipid syndrome (APS). aPL can be detected by immunological methods [e.g., anticardiolipin antibodies (aCL)] or by functional methods that exploit the effect of aPL on blood coagulation [lupus anticoagulant (LA)]. Since aPL are heterogeneous, numerous immunological and coagulation assays have been developed. These assays have not been fully standardized, and, therefore, problems such as high interlaboratory variation are relatively frequent. Recently, recommendations have been published regarding LA and aCL testing. Not all aPL are pathogenic. However, when they are not associated with infections, they have a role in the pathogenesis of APS. Clinical and experimental data have shown that aPL exert their pathogenic activity by interfering with the function of coagulation factors, such as thrombin and factors X, XI and XII, and with the function of anticoagulant proteins of the protein C system. In addition, aPL interaction with platelets and endothelial cells induces a pro-adhesive activated phenotype.

Controversies and unresolved issues in antiphospholipid syndrome pathogenesis and management

While much is understood concerning the clinical features of patients with antiphospholipid syndrome (APS), many issues remain. The proper designation of patients with "definite" APS and the correct categorization of patients by both laboratory and clinical features are matters of ongoing debate. Recent proposals have identified new subsets of patients who have many typical features of APS but either do not fit the criteria for a "definite" diagnosis or have initially negative laboratory tests for antiphospholipid antibodies. Meanwhile, decisions about laboratory tests are based on expert opinion, rather than the results of controlled trials. As for treatment, many guidelines are offered, but few are backed by data from strong clinical trials. This article summarizes the clinical questions remaining to be answered and debates concerning pathogenesis, diagnosis, and management.

Difficulties in eliciting broadly neutralizing anti-HIV antibodies are not explained by cardiolipin autoreactivity

OBJECTIVE

In a recent report [Haynes et al. Science 2005; 308:1906-1908], difficulties in eliciting broadly neutralizing antibodies to HIV were linked to the binding of prototypic broadly neutralizing monoclonal antibodies to autoantigens and in particular, to the binding of two antigp41 antibodies, 2F5 and 4E10, to the autoantigen cardiolipin. We used a number of assays to understand whether 2F5 and 4E10 are autoreactive, polyreactive, or have a generalized affinity for lipids that may facilitate recognition of their membrane proximal epitopes.

METHODS

2F5 and 4E10 were evaluated for autoreactivity using diagnostic assays developed to detect serum antibodies associated with antiphospholipid syndrome (APS). As an indication of polyreactivity, we measured the binding of 2F5 and 4E10 to liposomal bilayers of differing composition using surface plasmon resonance (SPR) spectroscopy and to protein microarrays using biochip technology.

RESULTS

2F5 showed completely negative results in the APS and SPR studies, indicating that it is neither autoreactive nor absolutely requires phospholipid binding for epitope recognition. In contrast, 4E10 bound to more than one lipid and showed weak activity in the APS studies. The activity displayed by 4E10 more closely resembles that of antiphospholipid antibodies elicited during many infections than that of autoimmune APS antibodies, at variance with the notion that difficulites in eliciting 4E10-like antibodies can be attributed to tolerance mechanisms. The microarray studies further indicated that broadly neutralizing anti-HIV mAb are not exceptionally polyreactive.

CONCLUSION

These results suggest that autoantigen mimicry cannot be reliably invoked as a general mechanism for HIV immune evasion.

Antiphospholipid syndrome: An evolving story

Antiphospholipid Syndrome (APS) is a form of immune mediated thrombophilia, presenting as recurrent thrombotic events and pregnancy morbidity, in association with positive laboratory tests for antiphospholipid antibodies (APA) in the form of Lupus Anticoagulant (LA) or anticardiolipin antibodies(ACA). Insights into the pathophysiology of the condition suggest that some antibodies are prothrombotic in vivo, and that the mechanism of thrombosis is likely to be multifactorial. APS has a broad spectrum of clinical presentations, and the laboratory diagnosis can be difficult due to heterogeneity of APAs and poor standardisation of laboratory tests. Anticoagulation is the mainstay of the management of the thrombotic and obstetric complications of APS. The risk of recurrent thrombosis appears to be high, and the duration and intensity of therapy remains controversial. Randomised controlled trials have shown that standard intensity anticoagulation is adequate in most cases of venous thrombosis. Further trials are required to establish whether high intensity coagulation is of benefit in recurrent or arterial thrombosis. The optimal management of recurrent fetal loss is debated and large studies are required to establish a clear benefit of heparin and aspirin over aspirin alone or supportive care.

Association between anticardiolipin antibodies and recurrent cardiac events in patients with acute coronary syndrome

To determine whether the presence of anticardiolipin (aCL) antibodies in patients with acute coronary syndrome is predictive of recurrent cardiac events in hospital stay and follow-up. The study population consisted of 80 patients with acute coronary syndrome. IgM and IgG aCL levels were determined before hospital discharge. We divided the patients into those with an aCL IgG >or= 40 IgG phospholipid units (group I, n = 30) and those with an aCL IgG < 40 IgG phospholipid units (group II, n = 50). All patients underwent coronary angiography. Follow-up coronary angiography was performed 12 months after percutaneous coronary intervention (PCI). Infectious and autoimmune diseases were exclusion criteria. Patients were observed to determine overall mortality, reinfarction, and restenosis. There were no differences between the groups with respect to the prevalence of hypertension, diabetes mellitus, and cigarette smoking, sex, or ejection fraction. The prevalence of left ventricular thrombus was similar between the groups (group I: 16% versus group II: 16.7%, P > 0.05). Although the presence of left atrial thrombus was much more frequent in cardiolipin positive patients (13% versus 4%, respectively), the difference was not statistically significant (P = 0.19). Restenosis was observed in 40% of the cardiolipin positive patients and 14% of the cardiolipin negative patients (P < 0.01). There was no significant association between reinfarction and anticardiolipin positivity during follow-up (26% versus 10%, P > 0.05). In group I patients, in-hospital mortality was somewhat more frequent compared to group II patients (4% versus 10%), but the difference was not statistically significant (P = 0.27). One year mortality was similar between the groups. These results suggest that 1) restenosis occurs more frequently in anticardiolipin positive patients and 2) no association is evident between positive aCL and mortality, reinfarction, and intracardiac thrombus.

International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS)

New clinical, laboratory and experimental insights, since the 1999 publication of the Sapporo preliminary classification criteria for antiphospholipid syndrome (APS), had been addressed at a workshop in Sydney, Australia, before the Eleventh International Congress on antiphospholipid antibodies. In this document, we appraise the existing evidence on clinical and laboratory features of APS addressed during the forum. Based on this, we propose amendments to the Sapporo criteria. We also provide definitions on features of APS that were not included in the updated criteria.

Anti-phospholipid antibodies in serum from patients with Guillain-Barré syndrome

OBJECTIVE

The Guillain-Barré syndrome (GBS) is an acute inflammatory polyneuropathy related to autoimmunity. However, no conclusive etiological concept has yet been found. We examined the variation in autoantibodies to lipids in serum of GBS patients in response to the course of the disease but investigated titer modifications during treatment with gamma-globulin.

DESIGN AND SETTING

Prospective clinical study in a 14-bed general ICU.

PATIENTS

Nine patients with GBS and nine controls were included in the study.

MEASUREMENTS AND RESULTS

Four blood samples were obtained before and after treatment. Serum samples, diluted 1:60, were tested by enzyme-linked immunosorbent assay for IgM, IgA, and IgG antibodies to phosphatidylcholine, phosphatidylinositol, cardiolipin, phosphatidic acid, phosphatidylserine, phosphatidylglycerol, phosphatidylethanolamine, sphingomyelin, and gangliosides. Anti-phospholipid antibodies of the IgM, IgA, and IgG families were detected in all GBS patients but in none of the controls. Phosphatidylinositol, cardiolipin, phosphatidylcholine, and phosphatidic acid were the main antigens. All patients developed anti-phosphatidylinositol antibodies of the IgM family and anti-cardiolipin antibodies of the IgA and IgG families. A decrease in the level of anti-phospholipid autoantibodies was observed after 1 day of treatment with gamma-globulin. Two days after ending gamma-globulin administration the IgG antibodies increased again.

CONCLUSIONS

Our findings suggest that in GBS there is an extensive immune reaction, which is altered after gamma-globulin treatment. Anti-cardiolipin and anti-phosphatidylinositol antibodies could be useful markers for the response to treatment.

Antiphospholipid syndrome: association between laboratory tests and clinical practice

Antiphospholipid antibodies are a wide and heterogeneous group of immunoglobulins, whose presence inpatients with arterial and venous thrombosis, and obstetrical complications defines the antiphospholipid syndrome. We systematically reviewed published articles on this syndrome to investigate the association between thrombosis and the most common antiphospholipid antibodies. Lupus anticoagulants were a clear risk factor for thrombosis, irrespective of the site and type of thrombosis, the presence of systemic lupus erythematosus, and the methods used to detect them. Anticardiolipin and anti 2-glycoprotein I antibodies were possible risk factors of thrombosis, at least in some selected situations. Conversely, the measurement of antiprothrombin antibodies was not helpful to define the patient's risk of thrombosis. These results are mainly due to the still far from optimal standardization of the methods to detect the various antiphospholipid antibodies.

Current debates in antiphospholipid syndrome: the acquired antibody-mediated thrombophilia

Antiphospholipid (APL) syndrome is the most common form of acquired thrombophilia. It can cause significant morbidity and even mortality. The term "APL antibodies" represents a heterogeneous group of antibodies associated with this disorder. Currently no single assay can identify every APL antibody. Clinically relevant APL antibodies are mainly anticardiolipin antibodies (ACA) detected by solid phase enzyme-linked immunosorbent assay (ELISA) and lupus anticoagulants (LA) demonstrated by in vitro coagulation assay. However, there are some other antibodies associated with the APL syndrome (i.e., subgroup APL antibodies). ACAs, LAs, and subgroup APL antibodies represent intersecting, but non-identical, subsets of autoantibodies. Thus, those autoantibodies may coexist or may occur independently. Any organ system and any size of vessel can be affected during the clinical course of the disease. Therefore, the APL syndrome can manifest itself in a wide variety of clinical thrombotic features. Fetal loss and pregnancy morbidity represent a specific challenge. Despite tremendous advances in the understanding of the pathogenesis of APL syndrome during the past decade, the mainstay of management is still anticoagulation. However, there is no general agreement regarding the duration and intensity of anti-coagulant therapy. In this review, we focused on the current dilemmas and their present clarifications in the wide clinicopathologic spectrum of APL syndrome and APL antibody-related distinct pathologic conditions.

Update on the immunology, diagnosis and management of systemic lupus erythematosus

Lupus occurs with a prevalence of 2-9 in 10,000 people, targeting female and indigenous populations in particular. Lupus and related systemic autoimmune syndromes (scleroderma, Sjögren's syndrome, rheumatoid arthritis and polymyositis) result from a similar set of genetically and environmentally modulated immune disturbances, and the diagnostic and management approach to these conditions is broadly comparable. Evanescent, vague symptoms, restrictive diagnostic criteria and low diagnostic suspicion might have resulted in the under-diagnosis of these problems in the past, imposing considerable burdens on sufferers and the community. Serological screening should be employed cautiously and wisely, given the rapidly occurring changes in methodology, which have lowered their specificity. Close liaison with the immunology laboratories performing these tests is therefore advisable. Clinicians should emphasize the improving prognosis of lupus and related conditions as a result of earlier disease detection, improved educational support systems and refined medical therapies.