A Quarter of a Century in Anticardiolipin Antibody Testing and Attempted Standardization Has Led Us to Here, which Is?

ABSTRACT

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 and recurrent pregnancy losses. The test was first established in 1983 as a radioimmunoassay and soon thereafter converted into an enzyme-linked immunosorbent assay (ELISA). The other test commonly used in the diagnosis of APS is the lupus anticoagulant (LA) test. The aCL ELISA is sensitive for the diagnosis of APS but lacks specificity. On the other hand, the LA assay, although more specific, is not as sensitive as the aCL ELISA. More specific tests are now available such as the anti-β2 glycoprotein I (anti-β2GPI) assay, the antiprothrombin assay, and other ELISAs that use negatively charged phospholipids instead of cardiolipin to coat the plates.

In the past 25 years, there have been numerous efforts to standardize aCL, LA, and anti-β2GPI tests but there are still reports of significant intra- and interlaboratory variation in results for all three assays.

This article discusses in detail the clinical value of these tests, technical problems associated with their use, the current laboratory classification criteria for diagnosis of APS, and possible new and better assays that will be available in the near future for diagnosis of APS.

KEYWORDS

Anticardiolipin antibodies - antiphospholipid syndrome - antiphospholipid antibodies - ELISA

REFERENCES

• 1 Harris E N. Antiphospholipid syndrome. In: Klippel JH, Dieppe PA Rheumatology. London, United Kingdom; Mosby-Year Book 1994: 32.1-32.6
• 2 Harris E N. Syndrome of the Black Swan.  Br J Rheumatol. 1987;  26 324-326
• 3 Pierangeli S S, Harris E N, Davis S A, DeLorenzo G. β₂glycoprotein I enhances cardiolipoin-binding activity but is not the antigen for antiphospholipid antibodies.  Br J Haematol. 1992;  82 565-570
• 4 McNeil H P, Simpson R J, Chesterman C N, Krilis S. Antiphospholipid antibodies are directed a complex of antigen that includes a lipid binding inhibitor of coagulation: β₂glycoprotein I (apolipoprotein H).  Proc Natl Acad Sci U S A. 1990;  87 4120-4124
• 5 Roubey R AS, Eisenberg R A, Harper M F, Winfield J B. “Anticardiolipin” antibodies recognize β₂glycoprotein I in the absence of phospholipid.  J Immunol. 1995;  154 954-960
• 6 Triplett D A, Brandt J T. Lupus anticoagulants: misnomer, paradox, riddle, epiphenomenon.  Hematol Pathol. 1988;  2 121-143
• 7 Moore J E, Mohr C F. Biologically false positive serologic tests for syphilis; type, incidence, and cause.  J Am Med Assoc. 1952;  150 467-473
• 8 Conley C L, Hartmann R C. A hemorrhagic disorder caused by circulating anticoagulant in patients with disseminated lupus erythematosus.  J Clin Invest. 1952;  31 621-622
• 9 Conley C L. Disorders of the blood in disseminated lupus erythematosus.  Am J Med. 1952;  13 1-2
• 10 Feinstein D I, Rapaport S I. Acquired inhibitors of blood coagulation.  Prog Hemost Thromb. 1972;  1 75-95
• 11 Bowie E J, Thompson Jr J H, Pascuzzi C A, Owen Jr C A. Thrombosis in systemic lupus erythematosus despite circulating anticoagulants.  J Lab Clin Med. 1963;  62 416-430
• 12 Mueh J R, Herbst K D, Rapaport S I. Thrombosis in patients with the lupus anticoagulant.  Ann Intern Med. 1980;  92 156-159
• 13 Harris E N, Gharavi A E, Boey M L et al.. Anticardiolipin antibodies: detection by radioimmunoassay and association with thrombosis in systemic lupus erythematosus.  Lancet. 1983;  26 1211-1214
• 14 Gharavi A E, Harris E N, Asherson R A, Hughes G RV. Anticardiolipin antibody isotype distribution and phospholipid specificity.  Ann Rheum Dis. 1987;  46 1-6
• 15 Mouritsen S, Hoier-Madson M, Wiik A, Orum O, Strandberg Pedersen N. The specificity of anti-cardiolipoin antibodies from syphilis patient and from patients with systemic lupus erythematosus.  Clin Exp Immunol. 1989;  76 178-183
• 16 Harris E N, Gharavi A E, Wasley G D, Hughes G RV. Use of enzyme-linked immunosorbent assay and of inhibition studies to distinguish between antibodies to cardiolipin from patients with syphilis or autoimmune disorders.  J Infect Dis. 1988;  157 23-31
• 17 Intrator L, Oksenhendler E, Desforges L. Anticardiolipin antibodies in HIV infected with or without autoimmune thrombocytopenia purpura.  Br J Haematol. 1988;  67 269-270
• 18 Canoso R E, Zon L I, Groopman J E. Anticardiolipin antibodies associated with HTLV-III infection.  Br J Haematol. 1987;  65 495-498
• 19 Galvez J, Martin I, Medino D, Pujol E. Thrombophlebitis in a patient with acute Q fever and anticardiolipin antibodies.  Med Clin (Barc). 1997;  108 396-397
• 20 Canoso R T, Sise H S. Chlorpromazin-induced lupus anticoagulant and associated immunologic anormalitis.  Am J Hematol. 1982;  13 121
• 21 Harris E N. Annotation: antiphospholipid antibodies.  Br J Haematol. 1990;  74 1-9
• 22 Galli M, Comfurius P, Maasen C, Hamker H C, Debates M H. van Breda-Vriesman. Anticardiolipin (ACA) antibodies directed not to cardiolipin but to a plasma protein cofactor.  Lancet. 1990;  336 1544-1547
• 23 Matsuura E, Igarashi Y, Fujimoto M, Ichikawa K, Koike T. Anticardiolipin antibodies directed not to cardiolipin but to a plasma protein cofactor.  Lancet. 1990;  336 1547
• 24 McNeil H P, Simpson R H, Chesterman C N, Krilis S. Anti-phospholipid antibodies are directed against a complex antigen that includes a lipid binding inhibitor of coagulation: β₂glycoprotein I (apolipoprotein H).  Proc Natl Acad Sci U S A. 1990;  87 4120-4124
• 25 Nimpf J, Wurm H, Kostner G M. Interaction of β₂glycoprotein I with human blood platelets: influence upon the ADP-induced aggregation.  Thromb Haemost. 1985;  54 397-401
• 26 Harris E N, Gharavi A E, Patel S, Hughes G RC. Evaluation of the anticardiolipin antibody test: report of an international workshop held April 4 1986.  Clin Exp Immunol. 1987;  68 215-222
• 27 Harris E N. The second international anticardiolipin standardization workshop: the Kingston Anticardiolipin Antibody Study (KAPS) group.  Am J Clin Pathol. 1990;  101 616-624
• 28 Pierangeli S S, Stewart M, Silva L K, Harris E N. Report of an anticardiolipin workshop during the VII^th International Symposium on Antiphospholipid Antibodies.  J Rheumatol. 1998;  25 156-162
• 29 Reber G, Arvieux J, Comby D et al.. Multicenter evaluation of nine commercial kits for the quantitation of anticardiolipin antibodies.  Thromb Haemost. 1995;  73 444-452
• 30 Harris E N, Pierangeli S, Birch D. Anticardiolipin wet workshop report: Vth International Symposium on Antiphospholipid Antibodies.  Am J Clin Pathol. 1994;  101 616-624
• 31 Derksen W, Erkan D, Kaplan V, Sammaritano L, Pierangeli S S, Lockshin M D. Real world experience with antiphospholipid antibodies (APL): how stable are APL over time? [abstract].  Arthritis Rheum. 2004;  50 S67
• 32 De Moerloose P, Reber G, Vogel J-J. Anticardiolipn antibody determination: comparison of three ELISA assays.  Clin Exp Rheumatol. 1990;  8 575-577
• 33 Favaloro E J, Silvestrini R. Assessing the usefulness of anticardiolipin antibody assays: a cautious approach is suggested by high variation and limited consensus in multilaboratory testing.  Am J Clin Pathol. 2002;  118 548-557
• 34 Wong R CW, Wilson R J, Pollock W, Steele R H, Gillis D. Anticardiolipin antibody testing and reporting practices among laboratories participating in a large external quality assurance program.  Pathology. 2004;  36 174-181
• 35 Tincani A, Allegri F, Sanmarco M et al.. Anticardiolipin antibody assay: a methodological analysis for a better consensus in routine determinations – a cooperative project of the European Antiphospholipid Forum.  Thromb Haemost. 2001;  86 575-583
• 36 Harris E N, Pierangeli S S. Revisiting the anticardiolipin test and its standardization.  Lupus. 2002;  11 269-275
• 37 Peaceman A H, Silver R K, MacGregor S N, Scool M L. Interlaboratory variation in antiphospholipid antibody testing.  Am J Obstet Gynecol. 1992;  144 1780-1784
• 38 Pierangeli S S, Gharavi M D, Harris E N. Testing for antiphospholipid antibodies: problems and solutions.  Clin Obstet Gynecol. 2001;  44 48-57
• 39 Kutteh W H, Franklin R D. Assessing the variation in antiphospholipid antibody (APA) assays: comparison of results from 10 centers.  Am J Obstet Gynecol. 2004;  191 440-448
• 40 Wilson W A, Gharavi A E, Koike T et al.. International consensus statement on preliminary classification for definite antiphospholipid syndrome.  Arthritis Rheum. 1999;  42 1309-1311
• 41 Miyakis S, Lockshin M D, Atsumi T et al.. International consensus statement on an update of the classification criteria for definite antiphospholipid syndrome (APS).  J Thromb Haemost. 2006;  4 295-306
• 42 Harris E N, Chan J KH, Asherson R, Aber V R, Gharavi A E, Hughes G RV. Thrombosis, recurrent fetal loss and thrombocytopenia: predictive value of the anti-cardiolipin test.  Arch Intern Med. 1986;  146 2153-2156
• 43 Escalante A, Brey R L, Mitchel B D, Dreiner U. Accuracy of anticardiolipin antibodies in identifying a history of thrombosis among patients with systemic lupus erythematosus.  Am J Med. 1995;  98 558-567
• 44 Levine S R, Salowich-Palm L, Sawaya K L et al.. IgG anticardiolipin antibody titer > 40 GPL and the risk of subsequent thrombo-occlusive events and death.  Stroke. 1997;  28 1660-1665
• 45 Silver R M, Porter T F, VanLeeuween I, Jeng G, Scott J R, Branch D W. Anticardiolipin antibodies: clinical consequences of “low titers”.  Obstet Gynecol. 1996;  87 494-500
• 46 Budd R, Harley E, Quarshie A, Henderson V, Harris E N, Pierangeli S SA. Re-appraisal of the normal cut-off assignment for anti-cardiolipin IgM tests.  J Thromb Haemost. 2006;  4 2210-2214
• 47 Arvieux J, Pouzol P, Roussel B, Jacob M C, Colomb M G. Lupus-like anticoagulant properties of murine monoclonal antibodies to β₂glycoprotein I.  Br J Haematol. 1992;  81 568-573
• 48 Harris E N, Gharavi A E, Loizou S et al.. Cross-reactivity of antiphospholipid antibodies.  J Clin Lab Immunol. 1985;  16 1-6
• 49 Oosting J D, Derksen R H, Bobbink I W, Hackeng J M, Bouma B N, deGroot P C. Antiphospholipid antibodies directed against a combination of phospholipids with prothrombin, protein C or protein S: an explanation for their pathogenic mechanism?.  Blood. 1993;  81 2618-2625
• 50 Bevers E, Galli M, Barbui T, Comfurius P, Zwaal R D. Lupus anticoagulant IgG's (LA) are not directed to phospholipid only, but to a complex of lipid-bound human prothrombin.  Thromb Haemost. 1991;  66 629-632
• 51 Atsumi A T, Amengual O, Yasuda S, Koike T. Antiprothrombin antibodies – are they worth assaying?.  Thromb Res. 2004;  114 L533
• 52 Ichikawa K, Tsutsumu A, Atsumi T et al.. A chimeric antibody with human gamma 1 constant region as a putative standard for assays that detect IgG β₂glycoprotein I antibodies.  Arthritis Rheum. 1999;  42 2461-2470
• 53 Greaves M, Cohen H, Machin S J, Mackie I. Guidelines on the investigation and management of the antiphospholipid syndrome.  Br J Haematol. 2000;  109 704-715
• 54 Triplett D A. Antiphospholipid antibodies.  Arch Pathol Lab Med. 2002;  126 1424-1429
• 55 Wong R CW, Adelstein S, Gillis D, Favaloro E J. Development of consensus guidelines for anticardiolipin antd lupus anticoagulant testing.  Semin Thromb Hemost. 2005;  31 39-48
• 56 Wilson W A, Faghri Z, Taheri Z, Gharavi A E. Significance of IgA antiphospholipid antibodies.  Lupus. 1998;  7(Suppl 2) S110
• 57 Selva-O'Callaghan A, Ordi-Ros J, Monegal-Ferran F et al.. IgA anticardiolipin antibodies—relation with other antiphospholipid antibodies and clinical significance.  Thromb Haemost. 1998;  79 282-285
• 58 Alarcon-Segovia D, Deleze M, Oria C V et al.. Antiphospholipid antibodies and the antiphospholipid syndrome in systemic lupus erythematosus.  Medicine. 1989;  68 353-365
• 59 Spadaro A, Riccieri V, Terracina S, Rinaldi T, Taccari E, Zoppini A. Class specific rheumatoid factors and antiphospholipid syndrome in systemic lupus erythematosus.  Lupus. 2000;  9 56-60
• 60 Weidmann C E, Wallace D J, Peter J B, Knight P J, Bear M B, Klinenberg J R. Studies of IgG, IgM and IgA antiphospholipid antibody isotypes in systemic lupus erythematosus.  J Rheumatol. 1988;  15 74-79
• 61 Wilson W A, Faghiri Z, Taheri F, Gharavi A E. Significance of IgA antiphospholipid antibodies.  Lupus. 1988;  7(Suppl 2) S110-S113
• 62 Lopez L R, Santos M, Espinoza L R, La Rosa F. Clinical significance of immunoglobulin A: versus immunoglobulins G and M anticardiolipin antibodies in patients with systemic lupus erythematosus: correlation with thrombosis, thrombocytopenia and recurrent abortion.  Coag Transf Med. 1992;  98 449-454
• 63 Molina J F, Gutierrez-Urena S, Molina J et al.. Variability of anticardiolipin antibody isotype distribution in 3 geographic populations of patients with systemic lupus erythematosus.  J Rheumatol. 1997;  7 291-296
• 64 Wong K L, Liu H W, Ho K, Chan K, Wong R. Anticardiolipin antibodies and lupus anticoagulant in Chinese patients with systemic lupus erythematosus.  J Rheumatol. 1991;  18 1187-1192
• 65 Cucurul E, Gharavi A E, Diri E, Mendez E, Kappoort D, Espinoza L E. IgA anticardiolipin and anti-β₂glycoprotein I are the most prevalent isotypes in African American patients with systemic lupus erythematosus.  Am J Med Sci. 1999;  318 53-60
• 66 Tajim C, Suzuki Y, Mizushima Y, Ichikawa Y. Clinical significance of immunoglobulin A antiphospholipid antibodies: possible association with skin manifestations and small vessel vasculitis.  J Rheumatol. 1998;  25 1730-1737
• 67 Kalunian K C, Peters J B, Middlekauff H R et al.. Clinical significance of a single test for anti-cardiolipin antibodies in patients with systemic lupus erythematosus.  Am J Med. 1988;  85 602-608
• 68 Bahar A M, Kwak J Y, Beer A E et al.. Antibodies to phospholipids and nuclear antigens in non-pregnant women with unexplained spontaneous recurrent abortions.  J Reprod Immunol. 1993;  24 213-222
• 69 Pierangeli S S, Liu X, Barker J H, Anderson G, Harris E N. Induction of thrombosis in a mouse model by IgG, IgM and IgA immunoglobulins from patients with the antiphospholipid syndrome.  Thromb Haemost. 1995;  74 1361-1367
• 70 Lee R M, Brown M A, Branch D W, Ward K, Silver R M. Anticardiolipin and anti-β₂-glycoprotein-I antibodies in preeclampsia.  Obstet Gynecol. 2003;  102 294-300
• 71 Walton S P, Pierangeli S S, Campbell A, Klein E, Burchitt B, Harris E N. Demonstration of antiphospholipid antibodies heterogeneity by phospholipid column chromatography and salt gradient elution.  Lupus. 1995;  4 263-271
• 72 Boey M L, Colaco C B, Gharavi A E, Elkon K B, Loizou S, Hughes G R. Thrombosis in systemic lupus erythematosus: striking association with the presence of circulating lupus anticoagulant.  Br J Med. 1983;  287 1021-1023
• 73 Brandt J T, Barna L K, Triplett D A. Laboratory identification of lupus anticoagulants: results of the Second International Workshop for Identification of Lupus Anticoagulants. On behalf of the Subcommittee on Lupus Anticoagulants/Antiphospholipid Antibodies of the ISTH.  Thromb Haemost. 1995;  74 1597-1603
• 74 Brandt J T, Triplett D A, Rock W A, Bovill E G, Arkin C F. Effect of lupus anticoagulants on the activated partial thromboplastin time. Results of the College of American Pathologists survey program.  Arch Pathol Lab Med. 1991;  115 109-114
• 75 Brandt J T, Triplett D A, Musgrave K, Orr C. The sensitivity of different coagulation reagents to the presence of lupus anticoagulants.  Arch Pathol Lab Med. 1987;  111 120-124
• 76 Denis-Magdelaine A, Flahault A, Verdy E. Sensitivity of sixteen APTT reagents for the presence of lupus anticoagulants.  Haemostasis. 1995;  25 98-105
• 77 Jacobsen E M, Barna-Cler L, Taylor J M, Triplett D A, Wisloff F. The Lupus Ratio test—an interlaboratory study on the detection of lupus anticoagulants by an APTT-based-integrated, and semi-quantitative test. Fifth International Survey of Lupus Anticoagulants–ISLA 5.  Thromb Haemost. 2000;  83 704-708
• 78 Galli M, Luciani D, Bertolini G, Barbui T. Lupus anticoagulants are stronger risk factors for thrombosis than anticardiolipin antibodies in the antiphospholipid syndrome: a systematic review of the literature.  Blood. 2003;  101 1827-1832
• 79 Opatrny L, David M, Kahn S R, Shrier I, Rey E. Association between antiphospholipid antibodies and recurrent fetal loss in women without autoimmune disease: a meta-analysis.  J Rheumatol. 2006;  33 2214-2221
• 80 McNeil H P, Chesterman C N, Krilis S A. Anticardiolipin antibodies and lupus anticoagulants comprise separate antibody subgroups with different phospholipid binding characteristics.  Br J Haematol. 1989;  73 506-513
• 81 Chamley L W, Pattison N S, McKay E J. Separation of lupus anticoagulant from anticardiolipin antibodies by ion exchange and gel filtration chromatography.  Haemostasis. 1991;  21 25-29
• 82 Derksen R H, Hasselaar P, Blokzijl L, Gmelig Meyling F H, deGroot P G. Coagulation screen is more specific than the anticardiolipin antibody ELISA in defining a thrombotic subset of lupus patients.  Ann Rheum Dis. 1988;  47 364-371
• 83 Nash M J, Camilleri R S, Kunka S, Mackie I J, Machin S J, Cohen H. The anticardiolipin assay is required for sensitive screening for antiphospholipid antibodies.  J Thromb Haemost. 2004;  2 1077-1081
• 84 Brandt J T, Triplett D A, Alving B, Scharrer I. Criteria for the diagnosis of lupus anticoagulants: an update. On behalf of the Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibody of the Scientific and Standardisation Committee of the ISTH.  Thromb Haemost. 1995;  74 1185-1190
• 85 The Lupus Anticoagulant Working Party . Detection of lupus like anticoagulant: current laboratory practice in the United Kingdom.  J Clin Pathol. 1990;  43 73-75
• 86 Exner T, Triplett D A, Taberner D, Machin S J. Guidelines for testing and revised criteria for lupus anticoagulants. SSC Subcommittee for the Standardization of Lupus Anticoagulants.  Thromb Haemost. 1991;  65 320-322
• 87 Lupus Anticoagulant Working Party, on behalf of the BCSH Haemostasis and Thrombosis Task Force . Guidelines on Haemostasis and Thrombosis Task Force. Guidelines on testing for the lupus anticoagulant.  J Clin Pathol. 1991;  44 885-889
• 88 Exner T, Triplett D A, Taberner D A, Howard M A, Harris E N. Comparison of test methods for the lupus anticoagulant: international survey on lupus anticoagulants-1 (ISLA-1).  Thromb Haemost. 1990;  64 478-484
• 89 Hemostasis Committee of the . “Societe Francaise de Biologie Clinique.” Laboratory heterogeneity of the lupus anticoagulant: a multicentre study using different clotting assays on a panel of 78 samples.  Thromb Res. 1992;  66 349-364
• 90 Working Group on Hemostasis of the Societe Francaise de Biologie Clinique . Comparison of a standardized procedure with current laboratory practices for the detection of lupus anticoagulant in France.  Thromb Haemost. 1993;  70 781-786
• 91 Brandt J T, Barna L K, Triplett D A. Laboratory identification of lupus anticoagulants: results of the second international workshop for identification of lupus anticoagulants. On behalf of the subcommittee in Lupus Anticoagulants/Antiphospholipid Antibodies of the ISTH.  Thromb Haemost. 1995;  74 1597-1603
• 92 Goudemand J, Caron C, De Prost D et al.. Evaluation of sensitivity and specificity of a standardized procedure using different reagents for the detection of lupus anticoagulants. The Working Group on Hemostasis of the Societe Francaise of Biologie Clinicque and for the Groupe d'Etudes surl Hemostase et la Thrombose.  Thromb Haemost. 1997;  77 336-342
• 93 Jennings I, Kitchen S, Woods T A, Preston F E, Greaves M. Potentially clinically important inaccuracies in testing for lupus anticoagulant: an analysis of results from three survey of the UK National External Quality Assessment Scheme (NEQAS) for Blood Coagulation.  Thromb Haemost. 1997;  77 934-937
• 94 Arnout J, Meijer P, Vermylen J. Lupus anticoagulant testing in Europe: an analysis of results from the first European Concerted Action on Thrombophilia (ECAT) survey using plasmas spiked with monoclonal antibodies against human β₂glycopotein I.  Thromb Haemost. 1999;  81 929-934
• 95 Tripodi A, Biosiolo A, Chantarangkul V, Pengo V. Lupus anticoagulant (LA) testing: performance of clinical laboratories assessed by a national survey using lyophilized affinity purified immunoglobulin with LA activity.  Clin Chem. 2003;  49 1608-1614
• 96 Jennings I, Greaves M, Mackie I J, Kitchen S, Woods T A, Preston F E. Lupus anticoagulant testing: improvements in performance in an UK NEQAS proficiency testing exercise after dissemination of national guidelines on laboratory methods.  Br J Haematol. 2002;  119 364-369
• 97 Rand J H, Wu X X, Lapinski R et al.. Detection of antibody-mediated reduction of annexin A5 anticoagulant activity in plasmas of patients with the antiphospholipid syndrome.  Blood. 2004;  104 2783-2790
• 98 Rote N S, Dostal-Johnson D, Branch D W. Antiphospholipid antibodies and recurrent pregnancy loss: correlation between the activated partial thromboplastin and antibodies against phosphatidylserine and cardiolipin.  Am J Obstet Gynecol. 1990;  163 575-584
• 99 Harris E N, Pierangeli S S. A more specific ELISA assay for the detection of antiphospholipid.  Clin Immunol Newsl. 1995;  15 26-28
• 100 Merkel P, Chang Y, Pierangeli S S, Harris E N, Polisson R P. Comparison between the standard anticardiolipin antibody test and a new phospholipids test in patients with connective tissue diseases.  J Rheumatol. 1999;  26 591-596
• 101 Roubey R AS, Eisenberg R A, Harper M F, Winfield J B. Anticardiolipin autoantibodies recognize β₂glycoprotein I in the absence of phospholipid: importance of antigen density and bivalent binding.  J Immunol. 1995;  154 954-960
• 102 Balestrieri G, Tincani A, Spatola L et al.. Anti-β₂glycoprotein I antibodies: a marker of antiphospholipid syndrome?.  Lupus. 1995;  4 122-130
• 103 Arvieux J, Pouzol P, Roussel B, Jacob M C, Colomb M G. Lupus-like anticoagulant properties of murine monoclonal antibodies to β₂glycoprotein I.  Br J Haematol. 1992;  81 568-573
• 104 Viard J P, Armoura Z, Bach J F. Association of anti-β₂glycoprotein with lupus circulating anticoagulant and thrombosis in SLE.  Am J Med. 1992;  93 181-186
• 105 Cabiedes J, Cabral A, Alarcon-Segovia D. Clinical manifestations of the antiphospholipid syndrome in patients with systemic lupus erythematosus associate more strongly with anti-β₂glycoprotein 1 than with antiphospholipid antibodies.  J Rheumatol. 1995;  22 1899-1906
• 106 Lewis S, Keil L B, Binder W L, De Bari V. Standardized measurement of major immunoglobulin class (IgG, IgA and IgM) antibodies to β₂glycoprotein 1 in patients with antiphospholipid syndrome.  J Clin Lab Anal. 1998;  12 293-297
• 107 Katano K, Aoki A, Sasa H, Ogasawara M, Matsuura E, Yagami Y. β₂glycoprotein I-dependent anticardiolipin antibodies as a predictor of adverse pregnancy outcomes in healthy pregnant women.  Hum Reprod. 1996;  11 509-512
• 108 Martinuzzo M E, Forastiero R R, Carreras L O. Anti-β₂glycoprotein antibodies: detection and association with thrombosis.  Br J Haematol. 1995;  89 397-402
• 109 Ogasawara M, Aoki K, Matsuura E, Sasa H, Yagami Y. Anti-β₂glycoprotein antibodies and lupus anticoagulant in patients with recurrent pregnancy loss: prevalence and clinical significance.  Lupus. 1996;  5 587-592
• 110 Tsusumi A, Matsuura E, Ichikawa K et al.. Antibodies to β₂glycoprotein I and clinical manifestations in patients with systemic lupus erythematosus.  Arthritis Rheum. 1996;  39 1466-1474
• 111 Matsuura E, Igarashi Y, Yasuda T, Triplett D A, Koike T. Anticardiolipin antibodies recognize β₂glycoprotein I structure altered by interacting with an oxygen modified solid phase surface.  J Exp Med. 1994;  179 457-462
• 112 Galli M, Luciani B, Bertolini G, Barbui T. Anti-β₂glycopotein I, antiprothrombin antibodies and the risk of thrombosis in the antiphospholipid syndrome.  Blood. 2003;  102 2717-2723
• 113 Kaplan V, Erkan V, Derksen W L et al.. Real world experience with antiphospholipid antibodies (APL): how useful is anti-β₂glycoprotein (β₂GPI) test?.  , [abstract] Arthritis Rheum. 2004;  S67
• 114 Detkov D, Gil-Aguado A, Lavilla P, Cuesta M V, Fontan G, Pascual-Salcedo D. Do antibodies to β₂glycopotein I contribute to the better characterization of the antiphospholipid syndrome?.  Lupus. 1999;  8 430-438
• 115 Lee E Y, Lee C K, Lee T H et al.. Does the anti-β₂glycopotein I antibody provide additional information in patients with thrombosis.  Thromb Res. 2003;  111 29-32
• 116 Reber G, Schousboe I, Tincani A et al.. Inter-laboratory variability of anti-β₂glycoprotein I measurement. A collaborative study in the frame of the European Forum on Antiphospholipid Antibodies Standardization Group.  Thromb Haemost. 2002;  88 66-73
• 117 Reber G, Tincani A, Sanmarco M, de Moerloose P, Boffa M C. Proposals for the measurement of anti-β₂glycoprotein I antibodies. Standardization Group of the European Forum on Antiphospholipid Antibodies.  J Thromb Haemost. 2004;  2 1860-1862
• 118 Iverson G M, Matsuura E, Victoria E J, Cockerill K A, Linnik M D. The orientation of β₂GPI on the plate is important for the binding of anti-β₂GPI autoantibodies by ELISA.  J Autoimmun. 2002;  18 289-297
• 119 de Laat B, Derksen R H, De Groot P G. High-avidity anti-β₂glycoprotein I antibodies highly correlate with thrombosis in contrast to low-avidity anti-beta glycoprotein I antibodies.  J Thromb Haemost. 2006;  4 1619-1621
• 120 Santiago M, Martinelli R, Ko A et al.. Anti–β₂glycoprotein I and anticardiolipin antibodies in leptospirosis, syphilis and kala-azar.  Clin Exp Rheumatol. 2001;  19 425-430
• 121 Pierangeli S S, Henderson V, Pappalardo E et al.. Evaluation of several ELISA tests used in the diagnosis of antiphospholipid syndrome in a large cohort of patient samples. [abstract].  Arthritis Rheum. 2006;  54 S553
• 122 Yetman D L, Kutteh W H. Antiphospholipid antibody panels and recurrent pregnancy loss: prevalence of anticardiolipin antibodies compared with other antiphospholipid antibodies.  Fertil Steril. 1996;  66 540-546
• 123 Franklin R D, Kutteh W H. Antiphospholipid antibodies (APA) and recurrent pregnancy loss: treating a unique APA positive population.  Hum Reprod. 2002;  17 2981-2985
• 124 Sugi T, McIntyre J A. Certain autoantibodies to phosphatidylethanolamine (aPE) recognized factor XI and prekallikrein independently or in addition to the kininogens.  J Autoimmun. 2001;  17 207-214
• 125 Rao L VM, Hoang A D, Rapaport S I. Differences in interactions of lupus anticoagulant IgG with human prothrombin and bovine prothrombin.  Thromb Haemost. 1995;  73 668-674
• 126 Cesarman-Maus G, Rios-Luna N P, Deora A B et al.. Autoantibodies against the fibrinolytic receptor, annexin A2, in antiphospholipid syndrome.  Blood. 2006;  107 4375-4382
• 127 Atsumi A, Amengual O, Yasuda S, Koike T. Antiprothrombin antibodies—are they worth assaying?.  Thromb Res. 2004;  114 L533-L538
• 128 De Groot P G, Lutters B, Derksen R H et al.. Lupus anticoagulants and the risk of a first episode of deep venous thrombosis.  J Thromb Haemost. 2005;  3 1993-1997
• 129 Galli M, Luciani D, Bertolini G, Barbui T. Anti-β₂-glycoprotein I, antiprothrombin antibodies, and the risk of thrombosis in the antiphospholipid syndrome.  Blood. 2003;  102 2717-2723
• 130 Bizzaro N, Ghirardello A, Zampieri S et al.. Anti-prothrombin antibodies predict thrombosis in patients with systemic lupus erythematosus: a 15-year longitudinal study.  J Thromb Haemost. 2007;  5 1158-1164
• 131 Forastiero R, Martinuzzo M, Pombo G et al.. A prospective study of antibodies to β₂glycoprotein I and prothrombin and risk of thrombosis.  J Thromb Haemost. 2005;  3 1231-1238
• 132 Galli M, Borrelli G, Jacobsen E M et al.. Clinical significance of different antiphospholipid antibodies in the WAPS (warfarin in the antiphospholipid syndrome) study.  Blood. 2007;  110 1178-1183
• 133 Hudson M, Herr A L, Rauch J et al.. The presence of multiple prothrombotic risk factors is associated with a higher risk of thrombosis in individuals with anticardiolipin antibodies.  J Rheumatol. 2003;  30 2385-2391
• 134 Nojima J, Kuratsune H, Suehisa E et al.. Association between the prevalence of antibodies to β₂glycoprotein I, prothrombin, protein C, protein S, and annexin V in patients with systemic lupus erythematosus and thrombotic and thrombocytopenic complications.  Clin Chem. 2001;  47 1008-1015
• 135 de Laat B, Derksen R H, Urbanus R T, de Groot P G. IgG antibodies that recognize epitope Gly40-Arg43 in domain I of β₂glycoprotein I cause LA, and their presence correlates strongly with thrombosis.  Blood. 2005;  105 1540-1545
• 136 Ioannou Y, Pericleous C, Giles I, Latchman D S, Isenberg D A, Rahman A. Binding of antiphospholipid antibodies to discontinuous epitopes on domain I of human β₂glycoprotein I: mutation studies including residues R39 to R43.  Arthritis Rheum. 2007;  56 280-290