An in vitro model to mimic the thrombotic occlusion of small vessels in catastrophic antiphospholipid syndrome (CAPS).

Platelet activation and decrease in platelet count characterize the development of the most feared form of antiphospholipid syndrome (APS), i.e. catastrophic APS (CAPS). We aimed to assess if immuno-affinity purified anti-ß2-glycoprotein I (aß2GPI) antibodies enhance platelet activation inducing a significant flow obstruction in a platelet function analyzer (PFA). Affinity purified aß2GPI antibodies were obtained from 13 triple positive patients with a strong lupus anticoagulant (LA) and high titers of IgG anticardiolipin antibodies (aCL) and IgG aß2GPI. Platelet activation stimulated by adenosine diphosphate (ADP) in the presence or absence of aß2GPI was measured by the expression of P-selectin on platelet surface using flow cytometry. P-selectin expression remained close to baseline when normal whole blood was incubated with aß2GPI alone. When stimulated using aß2GPI combined with ADP, P-selectin expression (28.42 ± 5.15% vs. 20.98 ± 3.94%, p = 0.0076) was significantly higher than ADP alone. Closure time of normal whole blood passed through the PFA was significantly shorter using affinity purified aß2GPI than control IgG both in Col/ADP (160.1 ± 62.1 s vs. 218.6 ± 43.8 s; p = 0.021) and Col/EPI cartridges (149.5 ± 26.7 s vs. 186.9 ± 45.5 s; p = 0.030). Thus, platelet activation is enhanced by aß2GPI antibodies with a consequent premature closure in a PFA, possibly resembling that in microcirculation in patients with CAPS.

Factors associated with first thrombosis in patients presenting with obstetric antiphospholipid syndrome (APS) in the APS Alliance for Clinical Trials and International Networking Clinical Database and Repository: a retrospective study.

OBJECTIVE: To evaluate the subsequent rate of thrombosis among women with obstetric antiphospholipid syndrome (Ob-APS) in a multicentre database of antiphospholipid antibody (aPL)-positive patients, and the clinical utility of the adjusted Global Antiphospholipid Syndrome Score (aGAPSS), a validated tool to assess the likelihood of developing new thrombosis, in this group of patients. DESIGN: Retrospective study. SETTING: The Antiphospholipid Syndrome Alliance for Clinical Trials and International Networking Clinical Database and Repository. POPULATION: Women with Ob-APS. METHODS: Comparison of clinical and laboratory characteristics and measurement of aGAPSS in women with Ob-APS, with or without thrombosis, after initial pregnancy morbidity (PM). MAIN OUTCOME MEASURES: Risk factors for thrombosis and aGAPSS. RESULTS: Of 550 patients, 126 had Ob-APS; 74/126 (59%) presented with thrombosis, and 47 (63%) of these women developed thrombosis after initial PM, in a mean time of 7.6 ± 8.2 years (4.9/100 patient years). Younger age at diagnosis of Ob-APS, additional cardiovascular risk factors, superficial vein thrombosis, heart valve disease, and multiple aPL positivity increased the risk of first thrombosis after PM. Women with thrombosis after PM had a higher aGAPSS compared with women with Ob-APS alone [median 11.5 (4-16) versus 9 (4-13); P = 0.0089]. CONCLUSION: Based on a retrospective analysis of our multicentre aPL database, 63% of women with Ob-APS developed thrombosis after initial obstetric morbidity; additional thrombosis risk factors, selected clinical manifestations, and high-risk aPL profile increased the risk. Women with subsequent thrombosis after Ob-APS had a higher aGAPSS at entry to the registry. We believe that aGAPSS is a valid tool to improve risk stratification in aPL-positive women. TWEETABLE ABSTRACT: More than 60% of women with obstetric antiphospholipid syndrome had thrombosis after initial pregnancy morbidity.

Population differences in S-warfarin pharmacokinetics among African Americans, Asians and whites: their influence on pharmacogenetic dosing algorithms.

Using population pharmacokinetic analysis (PPK), we attempted to identify predictors of S-warfarin clearance (CL(S)) and to clarify population differences in S-warfarin pharmacokinetics among a cohort of 378 African American, Asian and white patients. Significant predictors of CL(S) included clinical (age, body weight and sex) and genotypic (CYP2C9*2,*3 and *8) factors, as well as African American ethnicity, the median CL(S) being 30% lower in the latter than in Asians and whites (170 versus 243 and 250 ml h-1, P<0.01). The plasma S-warfarin (Cp(S)) time courses following the genotype-based dosing algorithms simulated using the PPK estimates showed African Americans with CYP2C9*1/*1 and any of the VKORC1 genotypes would have an average Cp(S) at steady state 1.5-1.8 times higher than in Asians and whites. These results indicate warfarin dosing algorithms should be evaluated in each respective ethnic population. Further study of a large African American cohort will be necessary to confirm the present findings.

The role of platelets in antiphospholipid syndrome.

Despite extensive research, the pathogenesis of antiphospholipid syndrome (APS) remains obscure in many aspects. However, it is widely accepted that thrombosis is the result of a hypercoagulable state caused by antibodies directed against ß2-glycoprotein I (ß2-GPI), a protein whose physiological role is unknown. Although underestimated, platelets may be involved in APS and its thrombotic manifestations, especially arterial, in several ways. Thrombocytopenia is the most relevant non-criteria manifestation of APS, possibly caused by direct binding of anti-ß2-GPI antibodies or anti-ß2-GPI-ß2-GPI complexes. On the other hand, platelets may have a key role in APS-related thrombosis due to the presence of multiple receptors that can interact with anti-ß2-GPI antibodies (especially apolipoprotein E receptor 2' (apoER2') and glycoprotein Ibα (GPIbα)) with consequent release of different procoagulant mediators such as thromboxane B2, platelet factor 4 (PF4), and platelet factor 4 variant (CXCL4L1). The aim of this review is to put together evidence on the possible role of platelets in APS and to stimulate further research on the issue.

Efficacy and safety of rivaroxaban vs warfarin in high-risk patients with antiphospholipid syndrome: Rationale and design of the Trial on Rivaroxaban in AntiPhospholipid Syndrome (TRAPS) trial.

BACKGROUND: New oral anticoagulants may simplify long-term therapy in conditions requiring anticoagulation. Rivaroxaban is a direct factor Xa inhibitor that has been extensively studied and is now approved for the prevention and therapy of a number of thromboembolic conditions. OBJECTIVE AND METHODS: This is a multicentre, randomized, open-label, study that will evaluate if Rivaroxaban 20 mg od (or 15 mg od in patients with moderate renal insufficiency) is non-inferior to warfarin (INR target 2.5), for the prevention of thromboembolic events, major bleeding and death in high risk (triple positive) patients with antiphospholipid syndrome. Secondary endpoints will assess the incidence of any individual component of the composite end point. An external adjudication committee will evaluate all suspected outcome events. This will be a unique trial, as it will enrol the biggest homogenous cohort of high risk APS individuals. CONCLUSION: The methods and the study design should be appropriate to achieve study results that are both scientifically valid and relevant to clinical practice.

Ferritin in the antiphospholipid syndrome and its catastrophic variant (cAPS).

BACKGROUND: Ferritin is an iron storage protein considered also as an acute phase reactant with high levels in various inflammatory conditions. Recently, a plausible role for ferritin in the pathogenesis of immune-mediated and especially autoimmune diseases has been suggested. However, the link between ferritin and the antiphospholipid syndrome (APS) has been rarely explored. Therefore, in the current study we evaluated ferritin levels and their correlation to clinical and serological manifestations in patients with APS. We further analyzed ferritin levels among patients with the catastrophic variant of APS (cAPS). METHODS: Ferritin levels were determined in serum samples of 176 APS patients and 98 matched healthy controls according to age and sex (LIAISON, DiaSorin, Italy). APS samples were further analyzed for antiphospholipid (anti-cardiolipin, anti- beta-2-glycoprotein, lupus anticoagulant) and anti-infectious antibodies (CMV, EBV, rubella, toxoplasma, HBV) (LIAISON, DiaSorin, Italy). Clinical, serological and demographic manifestations were recorded. An additional analysis of ferritin levels among 14 patients with cAPS was performed. RESULTS: Hyperferritinemia was present in 9% vs. 0% of APS patients and controls, respectively (p < 0.001). Among patients with APS, ferritin levels correlated with venous thrombosis, cardiac, neurological, and hematological manifestations and the presence of anti-CMV-IgM antibodies. Hyperferritinemia was present in 71% of cAPS patients, and ferritin levels among this subgroup were significantly higher compared with APS-non-cAPS patients (816 ± 847 ng/ml vs. 120 ± 230 ng/ml, p < 0.001). CONCLUSIONS: Herein, we found that hyperferritinemia correlates with the presence of APS, its clinical manifestations and specifically with the catastrophic variant of this disease. Hyperferritinemia was also linked with anti-CMV antibodies among patients with APS. These associations allude to a pathogenic role of ferritin in the pathogenesis of APS, and the plausible role of ferritin as a marker of ensuing cAPS, although further studies are needed to elucidate these associations.

Major bleeding in patients undergoing PCI and triple or dual antithrombotic therapy: a parallel-cohort study.

The combination of oral anticoagulants with dual antiplatelet therapy (DAT) in patients undergoing percutaneous coronary intervention with stent implantation (PCI-stenting) is subject to controversy due to the high risk of bleeding. In this multicenter retrospective parallel-group study, we compared the rate of adverse events in chronically anticoagulated patients who underwent PCI-stenting and were discharged on aspirin, clopidogrel and warfarin (triple antithrombotic therapy [TT] group) and were followed in Italian anticoagulation centers, with a parallel cohort of patients who underwent PCI-stenting and were discharged on DAT group. The primary endpoint was the incidence of major bleeding while the patients were in TT and DAT. A secondary endpoint was the occurrence of major ischemic adverse events (MACEs). The final cohort consisted of 229 TT patients and 231 DAT patients followed up for 6 and 7 months, respectively. There were 11 (4.8%; 9.1% patient/years) major bleeding events in the TT group (1 was fatal) as compared to 1 (0.4%; 0.7% patient/years) event in the DAT group (p = 0.003). Of the 28 (6.1%) MACE recorded during the follow-up, 12 (5.2%) occurred in the TT group and 16 (6.9%) in the DAT group. In conclusion, despite close monitoring of anticoagulated patients in dedicated centers, the major bleeding incidence remains high among unselected patients undergoing PCI-stenting and treated with TT. Any efforts to minimize these events should be pursued.

Standardization of lupus anticoagulant. The Lupus Anticoagulant Sensitivity Index (LASI).

Results for lupus anticoagulant (LA) are expressed as ratio of patient-to-normal clotting times (LA-ratio) according to the equation LA-ratio = (Patient(Clotting time)/Normal(Clotting time)). However, numerical results vary according to the method used for testing, thus making difficult the between-method and between-laboratory comparison of results. The hypothesis that the standardization model currently employed for the international normalized ratio for patients on warfarin is valid also for LA standardization has been taken into consideration. The model calls for the determination of a LA-sensitivity index (LASI) for each commercial method for LA detection against a common standard method. The LASI is then used to convert the LA-ratio into a scale called standardized LA-ratio (SLA-ratio) according to the equation SLA-ratio = (LA-ratio)(LASI). The model proved effective in minimizing the between-method variability of results for LA detection. If implemented it could be a valuable tool to improve the comparability of results obtained in different laboratories, to quantify the LA potency and thus pave the way to the organization of collaborative clinical trials aimed at assessing whether the potency of LA is a risk factor for clinical events.

Secondary prevention in thrombotic antiphospholipid syndrome.

Secondary prevention of venous thromboembolism in antiphospholipid syndrome (APS) is usually made using vitamin K antagonists (VKAs) to maintain an international normalized ratio (INR) between 2.0 and 3.0. The optimal intensity of anticoagulation was determined in two prospective randomized controlled trials, both excluding the benefit of more intense anticoagulation. The same regimen is also recommended in patients with APS and arterial thromboembolism as aspirin does not appear to protect against recurrences. The duration of treatment is usually indefinite because of a substantial risk of recurrence.

Antiphosphatidylserine/prothrombin antibodies in primary antiphospholipid syndrome.

Antiprothrombin (aPT) antibodies may be detected by an enzyme-linked immunosorbent assay (ELISA) using a purified antigen or a phosphatidylserine/prothrombin complex (aPS/PT). IgG/IgM antibodies directed against aPS/PT were assessed in 158 patients with primary antiphospholipid syndrome (PAPS). They were detected in 80/158 (50.6%) PAPS patients; IgG alone was positive in 12 (7.6%), IgM alone in 36 (22.8%), and both IgG and IgM isotypes in 32 (20.2%) PAPS patients. IgG and IgM aPS/PT were significantly associated with both vascular thrombosis and pregnancy morbidity. IgG aPS/PT was significantly associated with venous thrombosis (p = 0.023), whilst IgG and IgM aPS/PT were associated with arterial thrombosis (p < 0.001 and p < 0.001, respectively). Logistic regression analysis showed that IgM and IgG aPS/PT were independent risk factors for thrombosis (odds ratio (OR) 3.5 [95% confidence interval (CI) 1.6-7.9] and OR 4.1 [95% CI 1.4-11.7], respectively) and IgM aPS/PT was an independent risk factor for arterial thrombosis (OR 2.7 [95% CI 1.1-6.7]). In conclusion, these findings indicate that aPS/PT are clinically relevant in PAPS.

Interpretation of laboratory data and need for reference laboratories.

A single positive laboratory test among those exploring the presence of antiphospholipid antibodies is not associated with thromboembolic events and does not identify patients with antiphospholipid syndrome. On the other hand, more than one laboratory test positive, and in particular all three tests positive, is strongly associated to thromboembolic events and identifies high risk patients. Triple positivity is in fact related to the presence of a specific anti-ß2-glycoprotein I (anti-Domain I) antibody, also able to prolong coagulation tests. Monoclonal antibodies against Domain I with Lupus Anticoagulant activity might be candidate material for standardization of antiphospholipid assays. Much work remains to be done in this field.

Risk-based secondary prevention of obstetric antiphospholipid syndrome.

Treatment of pregnant women with antiphospholipid syndrome (APS) should be set apart from that from thrombotic APS patients. Patients with a history of pregnancy morbidity but no vascular thrombosis are usually treated with a prophylactic dose of heparin plus low-dose aspirin; whereas, those with previous vascular thrombosis alone or associated with previous pregnancy morbidity, are commonly treated with a therapeutic dose of heparin generally combined with low-dose aspirin. However, in about 20% of pregnant APS women these regimens fail. In this context, we conducted a case-control study on a large multicentre cohort of conventionally treated pregnancies to verify whether specific laboratory profiles and/or clinical characteristics are predictive of unsuccessful pregnancy outcome during conventional treatments. Multivariate analysis showed that pregnancy failure during conventional therapies was independently associated with a history of both thrombosis and pregnancy morbidity, the presence of systemic lupus erythematosus (SLE) or other systemic autoimmune diseases and triple antiphospholipid antibody positivity. With the aim to discover the most effective and safe treatments in high-risk pregnant APS women a large-scale multicentre study focusing on the effect of treatments on pregnancy outcome in women with APS and further risk factors for pregnancy failure has been designed.

A combination therapy to treat second-degree anti-Ro/La-related congenital heart block: a strategy to avoid stable third-degree heart block?

While mainly based on the use of fluorinated steroids, there is no standard management of anti-Ro/La-related congenital heart block (CHB). This is a report concerning two consecutive cases of anti-Ro/La-related second-degree block treated with betamethasone (4 mg/day), weekly plasmapheresis, and intravenous immunoglobulins (IVIGs; 1 g/kg) administered every 15 days, a therapy that was begun shortly after CHB was detected and continued until delivery. The newborns were also treated with IVIG (1 g/kg) soon after birth and continued fortnightly until the anti-Ro/La antibody levels became undetectable. In both cases second-degree AV block reverted to a stable sinus rhythm with a first-degree atrioventricular (AV) block. Moreover, there was no recurrence of CHB when therapy was suspended, as confirmed by a 29 month and an eight month follow-up, respectively.

Circulating ß2 glycoprotein I-IgG anti-ß2 glycoprotein I immunocomplexes in patients with definite antiphospholipid syndrome.

Beta2-glycoprotein I (ß(2)GPI), a relevant antigen in Antiphospholipid Syndrome (APS), binds anionic macromolecules including heparin (Hep). A possible formation of ternary complexes between ß(2)GPI, antibodies and Hep in APS is thus possible. The aim of this study was to evaluate Hep-ß(2)GPI interaction in patients with APS. The affinity of Heps of different length, including unfractionated Hep (UFH), low-molecular weight Hep (enoxaparin) and pentasaccharide (fondaparinux), to human ß(2)GPI was estimated by fluorescence spectroscopy, yielding dissociation constant (K(d)) values of 1.1, 24.0 and 89.4 µM, demonstrating that the longer UFH binds to ß(2)GPI far more tightly than the shorter ones. Plasma and protein G-purified IgGs from eight patients with APS (i.e. five with thromboembolic disease and three with catastrophic APS), were fractionated by affinity chromatography using a Hep (UFH)-bound column, eluted with a linear NaCl gradient. For each chromatographic analysis, fractions were collected in the whole NaCl gradient and tested by ELISA for the presence of ß(2)GPI and anti-ß(2)GPI IgG. The results of Hep-affinity chromatography and ELISAs concurrently indicate that either ß(2)GPI and anti-ß(2)GPI IgG elute from the Hep column in the same chromatographic peak, at a retention time identical to that of the purified, isolated ß(2)GPI, thus suggesting that circulating immunocomplexes containing ß(2)GPI are present in patients with APS.

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 ß(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.

'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-ß(2)glycoprotein I [anti-ß(2)GPI] 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-ß(2)GPI, 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 13(th) 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-ß(2)GPI 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-ß(2)GPI 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.

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

The antiphospholipid syndrome (APS) is defined by the presence of thrombosis and/or pregnancy morbidity in combination with the persistent presence of circulating antiphospholipid antibodies: lupus anticoagulant, anticardiolipin antibodies and/or anti-ß2-glycoprotein I antibodies in medium to high titers. The management of thrombosis in patients with APS is a subject of controversy. This set of recommendations is the result of an effort to produce guidelines for therapy within a group of specialist physicians in Cardiology, Neurology, Hematology, Rheumatology and Internal Medicine, with a clinical and research focus on APS.

Peripheral arterial disease has a strong impact on cardiovascular outcome in patients with acute coronary syndromes: from the START Antiplatelet registry.

BACKGROUND: Peripheral arterial disease (PAD) was reported to increase the risk of new cardiovascular events in patients with acute coronary syndromes (ACS). However, most of the evidence comes from randomized clinical trials. We aimed to assess the impact of PAD on cardiovascular outcome and treatment decisions in ACS patients in a current real-life setting. METHODS: START-ANTIPLATELET is a multicenter registry enrolling ACS patient. Baseline clinical characteristics and treatment at discharge were recorded and follow-up was repeated at 6-months and 1-year. PAD was defined as intermittent claudication and/or previous revascularization. RESULTS: Among 1442 patients enrolled, 103 (7.1%) had PAD. PAD patients were older (71.8 ± 10.6vs66.2 ± 12.6 yrs., p < 0.0001), more frequently hypertensive (90.3vs68.6%, p< 0.0001), hypercholesterolemic (66vs52%, p= 0.037), diabetic (51.5vs24%, p= 0.0001), obese (28.2vs19.3%, p= 0.029) and with previous TIA (7.8vs2.8%, p= 0.005) or stroke (11.7vs3.1%, p< 0.0001). Clinical presentation and acute treatment were similar in non-PAD and PAD patients, but the latter were discharged significantly less frequently on dual antiplatelet therapy (DAPT) (68.9vs85%, p= 0.005). After a median follow-up time of 11.1 months, major cardio/cerebrovascular event-free survival [MACCE, including cardiovascular death, MI, TIA and stroke, target-vessel revascularization (TVR) and major arterial ischemic events] was significantly shorter (9.0vs11.2 months, p= 0.02; HR 3.2, 2.4-8.4) in PAD patients and net adverse cardiovascular events (NACE = MACCE plus major hemorrhages) were significantly more frequent (19.1%vs10.5%, p = 0.049). CONCLUSIONS: PAD identifies a subgroup of ACS patients at significantly increased cardiovascular risk, but these patients tend to be undertreated. Patients admitted for ACS should be screened for PAD and optimal medical therapy at discharge should be implemented.

Standardized low-molecular-weight heparin bridging regimen in outpatients on oral anticoagulants undergoing invasive procedure or surgery: an inception cohort management study.

BACKGROUND: Bridging therapy with low-molecular-weight heparin is usually recommended in patients who must stop oral anticoagulants before surgical or invasive procedures. To date, there is no universally accepted bridging regimen tailored to the patient's thromboembolic risk. This prospective inception cohort management study was designed to assess the efficacy and safety of an individualized bridging protocol applied to outpatients. METHODS AND RESULTS: Oral anticoagulants were stopped 5 days before the procedure. Low-molecular-weight heparin was started 3 to 4 days before surgery and continued for 6 days after surgery at 70 anti-factor Xa U/kg twice daily in high-thromboembolic-risk patients and prophylactic once-daily doses in moderate- to low-risk patients. Oral anticoagulation was resumed the day after the procedure with a boost dose of 50% for 2 days and maintenance doses afterward. The patients were followed up for 30 days. Of the 1262 patients included in the study (only 15% had mechanical valves), 295 (23.4%) were high-thromboembolic-risk patients and 967 (76.6%) were moderate- to low-risk patients. In the intention-to-treat analysis, there were 5 thromboembolic events (0.4%; 95% confidence interval, 0.1 to 0.9), all in high-thromboembolic-risk patients. There were 15 major (1.2%; 95% confidence interval, 0.7 to 2.0) and 53 minor (4.2%; 95% confidence interval, 3.2 to 5.5) bleeding episodes. Major bleeding was associated with twice-daily low-molecular-weight heparin administration (high-risk patients) but not with the bleeding risk of the procedure. CONCLUSIONS: This management bridging protocol, tailored to patients' thromboembolic risk, appears to be feasible, effective, and safe for many patients, but safety in patients with mechanical prosthetic valves has not been conclusively established.

Antiphospholipid syndrome: critical analysis of the diagnostic path.

Antiphospholipid syndrome (APS) is diagnosed in the presence of vascular thrombosis or pregnancy morbidity occurring in patients with circulating antiphospholipid antibodies (lupus anticoagulant [LA] and/or IgG/IgM anticardiolipin [aCL] and/or IgG/IgM anti-beta2glycoprotein I [abeta2GPI] antibodies). Each test may identify different autoantibodies; a single test makes the diagnosis possible when positive on two or more occasions at least 12 weeks apart. However, single test positivity may be unrelated to pathogenic antibodies, which are now considered to be a subclass of abeta2GPI antibodies directed against the domain I of this protein. Conversely, all three positive tests identify a single class of abeta2GPI antibodies, thus identifying high-risk patients with APS.