Anti-cardiolipin antibody testing and reporting practices among laboratories participating in a large external Quality Assurance Program

Identification of high thrombotic risk triple-positive antiphospholipid syndrome patients is dependent on anti-cardiolipin and anti-β2glycoprotein I antibody detection assays

Essentials Triple-positivity is associated with a high risk for a first thrombotic event and recurrence. Identification of triple-positives is dependent on the solid phase assay used. In triple-positivity, IgM only adds value in thrombotic risk stratification together with IgG. Thrombotic risk in triple-positive patients with IgM only, depends on the platform.

ABSTRACT

Background The antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy morbidity with the persistent presence of antiphospholipid antibodies (aPL). Triple-positivity (i.e. positivity for lupus anticoagulant [LAC], anti-cardiolipin [aCL] and anti-β2glycoprotein I [aβ2GPI] antibodies) is associated with a high thrombotic risk. Objectives We investigated the variability in triple-positivity detection by measuring the same samples with four commercially available solid phase assays. In addition, the added clinical value of aPL in LAC-positive patients was investigated, as well as the association of IgM triple-positivity and thrombosis. Patients/Methods We included 851 patients from seven European medical centers. Anti-CL and aβ2GPI IgG/IgM antibodies were determined by four platforms: BioPlex® 2200, ImmunoCap® EliA, ACL AcuStar® and QUANTA Lite ELISA® . Results Triple-positivity detection by solid phase assays varied, ranging from 89 up to 118 in thrombotic APS patients (n = 258), of which 86 were detected independent of the platform. Lupus anticoagulant positivity resulted in an odds ratio (OR) for thrombosis of 3.4; triple-positivity (irrespective of the isotype) increased the OR from 4.3 up to 5.2, dependent on the platform. Triple-positivity solely for the IgM isotype did not increase the OR for thrombosis compared with LAC positivity. The highest OR for thrombosis was reached for positivity for IgG and IgM aβ2GPI and aCL (8.6 up to 28.9). Conclusions Triple-positivity proved to be highly associated with thrombosis, but identification is assay dependent. Within triple-positivity, IgM antibodies only have an added clinical value in patients positive for IgG antibodies.

‘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.

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.

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.

Real world experience with antiphospholipid antibody tests: how stable are results over time?

OBJECTIVE

To determine the stability and the degree of variation of antiphospholipid antibody (aPL) results over time in a large cohort of well evaluated aPL positive patients; and to analyse factors contributing to aPL variation and the validity of aPL in a real world setting in which aPL tests are done in multiple laboratories.

METHODS

The clinical characteristics, drug treatment, and 1652 data points for lupus anticoagulant (LA), anticardiolipin antibodies (aCL), and anti-beta2 glycoprotein I antibodies (anti-beta2GPI) were examined in 204 aPL positive patients; 81 of these met the Sapporo criteria for antiphospholipid syndrome (APS) and 123 were asymptomatic bearers of aPL.

RESULTS

87% of initially positive LA results, 88% of initially negative to low positive aCL results, 75% of initially moderate to high positive aCL results, 96% of initially negative to low positive anti-beta2GPI results, and 76% of initially moderate to high positive anti-beta2GPI results subsequently remained in the same range regardless of the laboratory performing the test. Aspirin, warfarin, and hydroxychloroquine use did not differ among patients whose aCL titres significantly decreased or increased or remained stable. On same day specimens, the consistency of aCL results among suppliers ranged from 64% to 88% and the correlation ranged from 0.5 to 0.8. Agreement was moderate for aCL IgG and aCL IgM; however, for aCL IgA agreement was marginal.

CONCLUSIONS

aPL results remained stable for at least three quarters of subsequent tests, regardless of the laboratory performing the test; the small amount of variation that occurred did not appear to be caused by aspirin, warfarin, or hydroxychloroquine use.

A multi-centre evaluation of the intra-assay and inter-assay variation of commercial and in-house anti-cardiolipin antibody assays

AIMS

To assess the intra-assay (intra-run) and inter-assay (inter-run) variation of commercial and in-house IgG and IgM anti-cardiolipin antibody (aCL) assays/kits, and to determine an appropriate maximum value for inclusion in consensus guidelines.

METHODS

Frozen aliquots of two patient specimens and one commercial control were sent to nine laboratories for the evaluation of eight commercial kits and one in-house assay. Intra-assay and inter-assay evaluations were performed with all three samples for IgG aCL, and one patient specimen for IgM aCL.

RESULTS

The IgG and IgM aCL values varied considerably between the nine assays/kits. The majority of assays/kits demonstrated less than 20% intra-assay and inter-assay variation, with lower intra-assay and inter-assay variation observed with the commercial control. Single calibrator assays were not consistently associated with higher inter-assay variation than multi-point calibrator assays.

CONCLUSIONS

An inter-assay coefficient of variation of 20% was determined to be an appropriate maximum value for inclusion in the Australasian aCL Working Party consensus guidelines. Improved standardisation between different assay/kits is still required.

Laboratory tests for the antiphospholipid syndrome: current concepts

There is increased scientific interest in the diagnosis of the antiphospholipid syndrome (APS), as therapeutic interventions can lead to substantial improvement in clinical outcome. As the clinical features of APS are far from specific, a sound laboratory method is needed to support or exclude the diagnosis. Two methods are currently used for the diagnosis of APS: (1). ELISA-based immunoassays for the detection of anticardiolipin (aCL) antibodies; and (2). clotting assays for determination of the lupus anticoagulant (LA). However, the first method is limited by a low specificity, and the second by low sensitivity. Furthermore, for both methods standardisation is unsatisfactory. Therefore, a number of new assays have been proposed as alternative or supplementary to aCL and LA tests. These include the anti-beta-2-glycoprotein I or antiprothrombin ELISAs, an ELISA utilising a phospholipid mixture, clotting assays with varying activators and assays utilising chromogenic substrates. This review presents a brief outline of APS, the autoantibodies associated with this syndrome, the basic principles of the standard assays used and a description of newer methods currently being validated.

Consensus guidelines on anti-cardiolipin antibody testing and reporting

Consensus guidelines on anti-cardiolipin antibody (aCL) testing have been developed to help minimise laboratory variation in the performance and reporting of aCL assays. These guidelines include minimum, optimum and optional recommendations for the following aspects of aCL testing and reporting: (1) isotype of aCL tested; (2) specimen type; (3) controls and assay precision; (4) calibrators; (5) patient samples; (6) rheumatoid factors and IgM aCL testing; (7) reporting of results; (8) cut-off values; and (9) interpretative comments.

ABBREVIATIONS

aCL, anti-cardiolipin antibodies; APS, anti-phospholipid antibody syndrome; ASCIA, Australasian Society of Clinical Immunology and Allergy; ASTH, Australasian Society of Thrombosis and Haemostasis; beta2-GPI=beta2-glycoprotein I; ELISA, enzyme-linked immunosorbent assay; NCCLS, National Committee for Clinical Laboratory Standards; HSANZ, Haematology Society of Australia and New Zealand; QAP, Quality Assurance Program; RCPA, Royal College of Pathologists of Australasia; %CV, inter-assay inter-run coefficient of variation.

Consensus guidelines for anticardiolipin antibody testing

Despite the use of standardized GPL and MPL units, significant inter-laboratory and inter-method variation in anticardiolipin antibody (aCL) testing still exists, limiting the clinical utility and inter-laboratory portability of test results. This article reviews published and unpublished guidelines (some developed using consensus procedures) that can be used to improve various aspects of: (1) specimen collection; (2) aCL assay manufacture and testing procedures; (3) quality control; and (4) interpretation (including reporting) of results; and in doing so, improve the consistency of aCL results between different laboratories, assays and runs. However, there is a still a need for consensus guidelines that combine and deal with all of the aforementioned aspects of aCL testing and reporting.