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.

Point of Care Testing (POCT) to assess drug concentration in patients treated with non-vitamin K antagonist oral anticoagulants (NOACs).

BACKGROUND: Non-vitamin K antagonist oral anticoagulants (NOACs) do not need routine laboratory monitoring but measurement of drug concentration is important in emergency conditions. Specific laboratory tests are not readily available or not implemented in every hospital. Point-of-Care Tests (POCT) may bridge this gap and be used as a bedside solution. OBJECTIVES: Feasibility of POCT to assess plasma levels of dabigatran, rivaroxaban and apixaban. PATIENTS/METHODS: Activated Coagulation Time-Low Range (ACT - LR) using a portable Hemochron Signature Elite for dabigatran and prothrombin time (expressed as INR) by Coaguchek XS Pro for rivaroxaban and apixaban were obtained at trough and peak in 136 consecutive patients taking NOACs (70 on dabigatran, 45 on rivaroxaban and 20 on apixaban). Using a paired study design, drug concentrations were concurrently determined by functional specific tests. RESULTS AND CONCLUSIONS: The correlation between NOACs concentration and the values obtained using the POCTs was high for dabigatran and rivaroxaban (r = 0.80 and r = 0.82, respectively) and low for apixaban (r = 0.21). ACT-LR ≤ 188 s better detected dabigatran levels ≤ 50 ng/ml, with a sensitivity of 87.5% and a specificity of 84.1%. ACT-LR values > 217 s better discriminated value of dabigatran > 200 ng/ml, with a sensitivity of 86.7% and a specificity of 81.4%. INR Coaguchek values ≤ 1.2 better identified patients with rivaroxaban values < 100 ng/ml, with sensitivity of 90%, specificity of 88.5%. This analysis was not possible for apixaban. CONCLUSION: In emergency situations POCT use may provide useful immediate information on dabigatran and rivaroxaban concentration.

Thrombocytopenia in high-risk patients with antiphospholipid syndrome.

Essentials The prevalence of thrombocytopenia in patients with antiphospholipid syndrome is not well defined. We studied triple positive patients with antiphospholipid syndrome and its catastrophic variant. Prevalence of thrombocytopenia was 6% and 100% in patients who developed the catastrophic form. In triple positive patients thrombocytopenia is low and platelets drop during the catastrophic form. SUMMARY: Background Thrombocytopenia is the most common non-criteria hematological feature in patients with antiphospholipid syndrome (APS). This condition is more common in patients with catastrophic APS (CAPS). Objectives To evaluate the prevalence of thrombocytopenia in a large series of high-risk patients with APS, and to assess the behavior of the platelet count during CAPS. Methods/Patients This was a cross-sectional study in which we analyzed the platelet counts of a homogeneous group of high-risk APS patients (triple-positive). Six of these patients developed a catastrophic phase of the disease, and the platelet count was recorded before the acute phase, during the acute phase, and at recovery. Results The mean platelet count in 119 high-risk triple-positive patients was 210 × 109 L-1 . With a cut-off value for thrombocytopenia of 100 × 109 L-1 , the prevalence of thrombocytopenia was 6% (seven patients). No difference between primary APS and secondary APS was found. In patients who suffered from CAPS, a significant decrease from the basal count (212 ± 51 × 109 L-1 ) to that at the time of diagnosis (60 ± 33 × 109 L-1 ) was observed. The platelet count became normal again at the time of complete remission (220 ± 57 × 109 L-1 ). A decrease in platelet count always preceded the full clinical picture. Conclusions This study shows that, in high-risk APS patients, the prevalence of thrombocytopenia is low. A decrease in platelet count was observed in all of the patients who developed the catastrophic form of the disease. A decrease in platelet count in high-risk APS patients should be considered a warning signal for disease progression to CAPS.

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.

APS - Diagnostics and challenges for the future.

Diagnosis of antiphospholipid syndrome (APS) is essentially based on the detection of circulating antiphospholipid (aPL) antibodies. Progress have been made on the standardization of tests exploring the presence of aPL as guidelines on coagulation and immunological tests were recently published in the literature. Clinical relevance of aPL profile has come from prospective cohort studies in populations with a homogeneous antibody profile supporting the view that triple positivity is a high risk pattern in patients and carriers. In addition to the classic ones, several other tests have been proposed for the diagnosis of APS. The detection of antibodies directed to domain 1 and 4/5 of ß2-Glycoprotein I (ß2GP1) were found to be particularly sound. Several issues remain to be addressed. We do not yet know what is the physiological function of ß2GP1 and the pathophysiology of thrombosis and pregnancy loss in these patients. Moreover, treatment is poorly defined especially in the case of feared catastrophic APS.

Laboratory testing for antiphospholipid syndrome.

This is a practical report on laboratory tests for the diagnosis of antiphospholipid syndrome (APS). After a general definition of APS, this study deals with appropriateness and timing in requesting the determination of antiphospholipid (aPL) antibodies. Lupus anticoagulant (LAC), anticardiolipin (aCL), and anti ß2-glycoprotein I (aßGPI) are the mandatory tests to be performed, while other tests are not yet validated for clinical use. Interpretation of results is an important discussed issue that implies a close liaison between clinical pathologists and clinicians. Finally, a personal definition of APS according to aPL antibody profile closes the manuscript.

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.

Antibodies to Domain 4/5 (Dm4/5) of ß2-Glycoprotein 1 (ß2GP1) in different antiphospholipid (aPL) antibody profiles.

BACKGROUND: Determination of the three recommended tests for the diagnosis of antiphospholipid syndrome [Lupus Anticoagulant (LA), anticardiolipin (aCL) and anti ß2-Glycoprotein 1 (aß2GP1) antibodies] allow physicians to allocate patients into classification (risk) categories. OBJECTIVES: To measure antibodies of IgG isotype directed towards Domain 4/5 (Dm4/5) of ß2GP1. PATIENTS/METHODS: In this cross-sectional study we measured IgG aß2GP1-Dm4/5 in a group of individuals positive for IgG aß2GP1 and classified as triple (LAC+, IgG aCL+, IgG aß2GP1+, n=32), double (LAC-, IgG aCL+, IgG aß2GP1+, n=23) or single positive (LA-, IgG aCL-, IgG aß2GP1+, n=10). RESULTS: Geometric mean and standard deviation of IgG aß2GP1 values expressed as Chemiluminescent Units (CU) in triple, double, single positive groups and in 40 healthy individuals were 1795±783, 321±181, 29±8 and 5.0±1.0, respectively (ANOVA p<0.0001). Geometric mean and standard deviation of IgG aß2GP1-Dm4/5 expressed as Optical Density (OD) in triple, double and single positive groups and in 40 healthy individuals were 0.16±0.13, 0.16±0.15 and 0.26±0.15, 0.13±0,11, respectively (ANOVA p<0.002). Individuals in the single positive group, expressed significantly higher values with respect to triple (p=0.04) and double (p=0.03) positive groups. Approximate OD cut-off value (99° percentile) calculated in 40 normal control subjects is 0.404. Positivity to IgG aß2GP1-Dm4/5 according to this cutoff was found in only 5 individuals, 3 in triple positive and 2 in single positive groups and was not associated with thromboembolism. CONCLUSION: Mean level of IgG aß2GP1-Dm4/5 is higher in single positive group. There is no association between positivity to IgG aß2GP1-Dm4/5 and thromboembolic events.

The association between antiphospholipid antibodies and pregnancy morbidity, stroke, myocardial infarction, and deep vein thrombosis: a critical review of the literature.

In a previous systematic literature search, we demonstrated that the frequencies of antiphospholipid antibodies (aPL) in general-population patients with pregnancy morbidity (PM), deep vein thrombosis (DVT), myocardial infarction (MI), and stroke (ST) are 6%, 10%, 11%, and 14%. To determine the association between aPL and clinical outcomes, we conducted a follow-up analysis of the 120 studies included in the original paper. Based on the analysis of 81 studies, a significant difference in the frequency of aPL criteria tests between patients and controls emerged considering all the outcomes together (10% versus 3%). In particular, a significant difference was reported for overall PM, pregnancy loss (PrL), late PrL, severe preeclampsia (PEC), ST, MI, and DVT. No difference emerged for early PrL, intrauterine growth restriction (IUGR), PEC, eclampsia (EC), and HELLP. A positive association was found in more than half of the studies for overall PrL, severe PEC, HELLP, ST, MI, and DVT and in less than half for early and late PrL, PEC, EC, and IUGR. The positive association between aPL and clinical outcomes included in the antiphospholipid syndrome classification criteria is not supported by every study, being particularly inconsistent for early PL, IUGR, PEC, EC, and HELLP.

Antiphospholipid syndrome: antibodies to Domain 1 of ß2-glycoprotein 1 correctly classify patients at risk.

BACKGROUND: Determination of lupus anticoagulant (LA), anticardiolipin (aCL) and ß2-Glycoprotein 1 (aß2GP1) antibodies is mandatory to classify patients with antiphospholipid syndrome (APS) into risk categories. OBJECTIVES: To measure relevant antibodies, considered to be those of the IgG isotype directed towards ß2GP1 and particularly those directed to Domain 1 (Dm1) of the molecule. PATIENTS/METHODS: In this cross-sectional study we measured IgG aß2GP1-Dm1 by a chemiluminescent immunoassay in a group of individuals initially positive for IgG aß2GP1 and classified as triple (LAC+, IgG aCL+, IgG aß2GP1+, n = 32), double (LAC-, IgG aCL+, IgG aß2GP1+, n = 23) or single positive (LA-, IgG aCL-, IgG aß2GP1+, n = 10). RESULTS AND CONCLUSION: Geometric mean and standard deviation expressed as chemiluminescent units (CU) in triple, double and single positive groups were 273.0 ± 6.2, 18.2 ± 9.6 and 4.4 ± 2.2, respectively. The geometric mean obtained in 40 healthy subjects was 2.0 ± 2.0. Mean CU values were significantly different among groups and with respect to values found in 40 healthy subjects (P < 0.0001). Positive values of IgG aß2GP1-Dm1 (above 14.2 CU) were found in 45 individuals while 20 individuals (20/65 = 30.8%) positive for IgG aß2GP1 were negative for IgG aß2GPI-Dm1. There was a significant association between positive IgG aß2GP1-Dm1 and thromboembolic events (P = 0.001). Positive and negative values of IgG aß2GP1-Dm1 were consistently confirmed after 12 weeks, with only three low positive values being negative after 12 weeks. In conclusion, IgG aß2GP1-Dm1 seems a robust and reproducible test that in association with the classic tests may be useful in clinical practice in identifying individuals at high risk of developing thromboembolic events.

Confirmation of initial antiphospholipid antibody positivity depends on the antiphospholipid antibody profile.

BACKGROUND: The revised classification criteria for the antiphospholipid syndrome state that antiphospholipid (aPL) antibodies (lupus anticoagulant [LAC] and/or anticardiolipin [aCL] and/or anti-ß2 -glycoprotein I [aß2 GPI] antibodies) should be detected on two or more occasions at least 12 weeks apart. Consequently, classification of patient risk and adequacy of treatment may be deferred by 3 months. OBJECTIVES: In order to early classify patient risk, we evaluated whether aPL positivity confirmation is related to aPL antibody profiles. PATIENTS AND METHODS: Consecutive patients referred to our center who were initially positive in one or more tests exploring the presence of aPL were tested after 3 months. During a 4-year period, 225 patients were initially positive in one or more tests, and 161 were available for confirmation after 3 months. Patients were classified as triple-positive (n = 54: LAC(+) , aCL(+) , aß2 GPI(+) , same isotype), double-positive (n = 50: LAC(-) , aCL(+) , aß2 GPI(+) , same isotype) and single-positive (n = 53: LAC or aCL or aß2 GPI antibodies as the sole positive test). RESULTS: Among subjects with triple positivity at initial testing, 98% (53 of 54) had their aPL profile confirmed after 12 weeks. The double-positive and single-positive groups had data confirmed in 42 of 50 (84%) and 23 of 57 (40%) subjects, respectively. CONCLUSIONS: Our results show that high-risk subjects with triple-positive aPL profiles are identified early, at the time of the initial screening tests.

ß2 -Glycoprotein I binds to thrombin and selectively inhibits the enzyme procoagulant functions.

BACKGROUND: This work was aimed at characterizing the interaction of ß(2)-glycoprotein I (ß(2)GPI), an abundant plasma protein of unknown function, with human thrombin, the final effector protease in the coagulation cascade. METHODS: The ß(2)GPI-thrombin interaction was studied by surface plasmon resonance (SPR), fluorescence, and molecular modeling. The effect of ß(2)GPI on the procoagulant (fibrin generation and platelet aggregation) and anticoagulant (protein C activation) functions of thrombin were investigated with turbidimetric, immunocytofluorimetric and enzymatic assays. RESULTS: SPR and fluorescence data indicated that ß(2)GPI tightly bound thrombin (K(d) = 34 nM) by interacting with both protease exosites, while leaving the active site accessible. This picture is fully consistent with the theoretical model of the ß(2)GPI-thrombin complex. In particular, blockage of thrombin exosites with binders specific for exosite-1 (hirugen and HD1 aptamer) or exosite-2 (fibrinogen γ'-peptide and HD22 aptamer) impaired the ß2 GPI-thrombin interaction. Identical results were obtained with thrombin mutants having one of the two exosites selectively compromised by mutation (Arg73Ala and Arg101Ala). Fluorescence measurements indicated that ß(2)GPI did not affect the affinity of the enzyme for active site inhibitors, such as p-aminobenzamidine and the hirudin(1-47) domain, in agreement with the structural model. ß(2)GPI dose-dependently prolonged the thrombin clotting time and ecarin clotting time in ß(2)GPI-deficient plasma. ß(2)GPI inhibited thrombin-induced platelet aggregation (IC50 = 0.36 µM) by impairing thrombin cleavage of protease-activated receptor 1 (PAR1) (IC50 = 0.32 µM), both on gel-filtered platelets and in whole blood. Strikingly, ß(2) GPI did not affect thrombin-mediated generation of the anticoagulant protein C. CONCLUSIONS: ß(2) GPI functions as a physiologic anticoagulant by inhibiting the key procoagulant activities of thrombin without affecting its unique anticoagulant function.

Correct laboratory approach to APS diagnosis and monitoring.

Triple positivity (positive Lupus Anticoagulant, anticardiolipin and anti ß2-glycoptrotein I antibodies) identifies the pathogenic autoantibody (anti Domain I of ß2-glycoptroteinI) that is present in patients with definite Antiphospholipid Syndrome (APS). This is supported by the fact that aß2GPI antibodies obtained by affinity purification in these patients possess LA activity. Moreover, patients and carriers of this profile carry a much higher risk of thrombosis and pregnancy loss than APS patients with positivity for only one of the tests. Thus, very different risk categories exist among patients with APS as well as among carriers of aPL. Clinical studies and interventional trials should first take these high risk subjects into consideration.

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.

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.

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.

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.

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.

Antibodies to Domain I of ß(2)Glycoprotein I are in close relation to patients risk categories in Antiphospholipid Syndrome (APS).

INTRODUCTION: Antiphospholipid Syndrome (APS) is characterized by the presence of circulating antiphospholipid antibodies in patients with thrombosis or pregnancy morbidity. Antibodies involved in these disorders are mainly those directed against ß(2)-Glycoprotein I (ß(2)GPI) with the major epitope apparently located on discontinuous antigen with several parts of Domain I (DmI) involved. The relation between anti-DmI antibodies and patients' risk categories is unknown. MATERIALS AND METHODS: The synthetic full-length and correctly-folded DmI (1-64) to set up a competitive inhibition enzyme-linked immunoadsorbent assays (ELISA) was used. Plasma of 22 patients with APS and triple positivity [Lupus Anticoagulant positive (LAC+), IgG anti-cardiolipin positive (aCL+), IgG anti-ß(2)GPI positive (a ß(2)GPI +)], 15 with double positivity (IgG aCL+, IgG aß(2)GPI+), 9 with single positivity (IgG aß(2)GPI+) and 20 controls were evaluated. RESULTS: Median of percentage inhibition was 25.5% [interquartile range (IQR)17.2-33.0] in triple positive patients. Significantly lower inhibition was observed in patients with double positivity, median inhibition 5.0% (IQR 0.0-27.0) and in patients with single positivity median inhibition was 2.0% (IQR 0.5-8.0) (p<0.0001). No inhibition was detected in control subjects or using ß(2)GPI peptides (40-52 and 57-70), or when antithrombin, an insignificant control protein was used. CONCLUSIONS: High risk patients with APS and triple laboratory positivity as compared with double and single positivity patients have significantly higher titre of anti-DmI antibodies as evaluated by an inhibition test.