Which antiphospholipid antibody tests are most useful?

Antiphospholipid antibodies: paradigm in transition

OBJECTIVES

This is a critical review of anti-phospholipid antibodies (aPL). Most prior reviews focus on the aPL syndrome (APS), a thrombotic condition often marked by neurological disturbance. We bring to attention recent evidence that aPL may be equally relevant to non-thrombotic autoimmune conditions, notably, multiple sclerosis and ITP.

ORGANIZATION

After a brief history, the recent proliferation of aPL target antigens is reviewed. The implication is that many more exist. Theories of aPL in thrombosis are then reviewed, concluding that all have merit but that aPL may have more diverse pathological consequences than now recognized. Next, conflicting results are explained by methodological differences. The lupus anticoagulant (LA) is then discussed. LA is the best predictor of thrombosis, but why this is true is not settled. Finally, aPL in non-thrombotic disorders is reviewed.

CONCLUSION

The current paradigm of aPL holds that they are important in thrombosis, but they may have much wider clinical significance, possibly of special interest in neurology.

The prevalence and clinical significance of antiphospholipid antibodies in rheumatoid arthritis

Published data were reviewed to evaluate the occurrence of antiphospholipid antibodies (aPL) in rheumatoid arthritis (RA) patients and to investigate their clinical relevance in this population. The mean prevalence was calculated at 28% and the median was 22%. Few studies have found a relationship between aPL antibodies and thrombosis, particularly in combination with other risk factors. Conflicting results have been reported on the association of anticardiolipin (aCL) antibody positivity and neurologic symptoms, Reynaud's phenomenon, disease activity, radiographic erosions, extra-articular RA manifestations, rheumatoid factor, and atherosclerosis. Some studies, however, suggest that there is a correlation present between those antibodies and C-reactive protein levels, rheumatoid nodules, and antinuclear antibodies. TNF-alpha blocking agents may cause an induction of aCL antibodies, but it seems like they do not cause any clinical features related to the antiphospholipid syndrome. Higher 17beta-estradiol levels were observed in aCL antibody-positive RA patients than in aCL antibody-negative patients and especially in premenopausal women, which may predispose to a more efficient immune response.

Primary antiphospholipid syndrome: A distinct entity?

Although antiphospholipid syndrome (APS) was first fully described in the context of connective tissue diseases such as systemic lupus erythematosus (SLE), it was soon recognised that the condition can exist on its own. APS appears to represent a clinical spectrum, both in terms of APS features and the presence of other autoimmune conditions. The clinical and serological characteristics of "primary" APS (PAPS) are similar to those of secondary APS, although the clinical features are more commonly recognised in the presence of another autoimmune or inflammatory condition. Furthermore, patients with PAPS may subsequently develop SLE. It is important to identify PAPS, since it is likely to be a contributing factor for a significant proportion of patients with a variety of vascular, neurological and other conditions. It may emerge as more common than secondary APS.

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.

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

AIMS

To investigate differences in anti-cardiolipin antibody (aCL) testing and reporting practices among diagnostic laboratories participating in the RCPA Quality Assurance Program (QAP) Immunology Program.

METHODS

A survey was sent to all 58 laboratories enrolled for aCL testing in the RCPA QAP Program requesting the following information: (1). manufacturer/type of assay; (2). isotype tested; (3). use of calibrators and controls; (4). whether calibrators, control and patient specimens were performed in singles or duplicates; (5). whether results were reported semi-quantitatively and/or numerically; (6). values used to define negative/positive and semi-quantitative cut-offs and how they were determined; and (7). whether interpretative comments were provided and their content.

RESULTS

Thirty-two surveys (55%) were received. Significant differences were present particularly in the following areas: (1). whether IgM isotype aCL testing was performed routinely or only on specific request; (2). whether controls/calibrators/specimens were tested in singles or duplicates; (3). whether results were reported numerically and/or semi-quantitatively; (4). the values used to define negative/positive and semi-quantitative range cut-offs; and (5). whether interpretative comments were provided and their content.

CONCLUSIONS

These differences in testing and reporting practices are likely to contribute to the variation in aCL results reported by different laboratories, particularly among those using the same assay.

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.

Single center review of clinicopathological characterization in 77 patients with positive lupus anticoagulant antibodies

BACKGROUND

The antiphospholipid syndrome (APS) is a thrombophillic disorder characterized by the presence of antiphospholipid antibodies (APA). It often occurs in patients with systemic lupus erythematosus (SLE) and may be associated with recurrent abortions and thrombocytopenia and, occasionally, catastrophic thrombotic events.

OBJECTIVES

To examine, retrospectively, the clinico-pathological features of patients with APS detected by the presence of the lupus anticoagulant (LAC).

METHODS

Patients were selected for study on the basis of a positive LAC test on review of the laboratory computer records of the King Faisal Specialist Hospital and Research Center. Following this, a clinical chart review was conducted in order to determine the clinical presentations, treatment and the course of patients identified. The information obtained was entered into an electronic database and subsequently analyzed.

RESULTS

Seventy-seven patients were identified and reviewed. Fifty-six (73%) were female and 16 (21%) were children less than 15-years-old. Thirty-two patients (42%) had no clinical events (incidental APS). The syndrome was classified as primary in 40 (52%) patients and secondary in 37 (48%). Out of the 45 (58%) patients who presented with symptoms related to APA 22 (49%) had thrombosis, 24 (53%) had pregnancy failure, and 4 (9%) presented with catastrophic APS. The activated partial thromboplastin time (aPTT) was elevated and not corrected by mixing with normal plasma in 47 (61%). On the other hand, the prothrombin time (PT) was normal in 66 (90%). There is a significant difference between aPTT and PT as a screening test with P value of < 0.0001. Tests for anticardiolipin antibodies (ACA) were positive in 39 patients (70%). Only 13 (17%) patients had thrombocytopenia. All patients who presented with thrombosis were treated with warfarin but only 5 (23%) had received aspirin. Out of the 22 patients presenting with thrombosis, 12 (55%) had one or more recurrent thrombotic events while only 6 (25%) out of the 24 patients who presented with pregnancy failure had events other than pregnancy failure. Fifty-two patients were followed up regularly and were alive.

CONCLUSIONS

We find that thrombosis, venous or arterial, and obstetric complications are the most frequent clinical findings in our patients with circulating LAC. Incidental APS is not an uncommon finding in patients screened for APS. There is a clear association between the presence of LAC and an abnormal aPTT, which is much less obvious with the PT.

Antiphospholipid antibodies in pediatrics

Antiphospholipid antibody syndrome has been associated with vascular thrombosis, thrombocytopenia, hemolytic anemia, livedo reticularis, neurologic disorders, and recurrent fetal loss. The diagnosis of antiphospholipid syndrome is given in the presence of an elevated anticardiolipin antibody lupus anticoagulant in addition to a thrombotic event. Antiphospholipid antibodies are responsible for a majority of thrombotic events in children. These antibodies can present as a primary syndrome or secondary to other diseases, such as systemic lupus erythematosus. Anticoagulation therapy with heparin and low-dose aspirin is the recommended treatment in pediatric patients.

Recent advances in the diagnosis of antiphospholipid syndrome

Antiphospholipid antibodies are autoantibodies directed against anionic phospholipids or protein-phospholipid complexes measured in solid-phase immunoassays such as anticardiolipin (aCL) antibody or detected in phospholipid-dependent clotting tests as lupus anticoagulant (LA). The term "antiphospholipid syndrome (APS)" was first coined to denote the clinical association between antiphospholipid antibodies and a syndrome of episodes of thrombosis in arteries and/or veins, pregnancy loss, and thrombocytopenia. The diagnosis of APS is based on the finding of "moderate-to-high" aCL antibody titer and/or an LA test with any one of the characteristic clinical features presented. Recently, the diagnostic criteria of APS was revised and several newer assays that use phosphatidylserine, a mixture of negatively charged phospholipids or beta2-glycoprotein 1 (beta2-GP1) have been proposed for more specific measurements of antibodies present in APS. In this section, recent progress in the laboratory diagnosis of antiphopholipid syndrome will be discussed.