The antiphospholipid antibody syndrome: A riddle wrapped in a mystery inside an enigma

The antiphospholipid antibody syndrome (APS) is the association of certain clinical features with the presence of antiphospholipid antibodies (APA) in the serum or plasma of affected individuals. APS may be primary or secondary to another disease, typically autoimmune diseases such as systemic lupus erythematosus (SLE).The prototypic clinical features are thrombotic events (venous and arterial) and pregnancy morbidity (recurrent fetal loss, severe preeclampsia, eclampsia, and multiple spontaneous abortions). The term antiphospholipid antibody is a misnomer since it now appears that APA are actually directed against protein phospholipid complexes. APA may also occur secondary to infections however these APA seem to be directed at phopsholipid only and are transient. Particular phospholipid-binding proteins associated with APS include beta 2-glycoprotein I (B2GPI), prothrombin, and annexin V. A recent International Consensus Statement defines Definite APS as the presence of certain clinical findings (either a thrombotic event and/or pregnancy morbidity) and the presence and persistence of laboratory evidence of APA [either the lupus anticoagulant (LA) and/or anticardiolipin antibodies (ACL)]. Other clinical features associated with APS include thrombocytopenia, various skin conditions, cardiac valvular diseases, and diverse neurological conditions as outlined in the main text. These other features may be part of APS but require further evidence to establish their pathological and clinical validity. Other laboratory tests of interest include anti-B2GPI, antiprothrombin, and antiphosphatidylserine antibodies. The diagnostic and clinical importance of these additional laboratory tests remains to be determined.APA are estimated to be present in up to 5% of the general population, with the prevalence increasing with age. APA are estimated to be present in 12% or more of patients with thrombosis. ACL are present in 12 to 30% of patients with SLE and LA are present in 15 to 34% of patients with SLE. There is often concordance between LA and ACL however this is not always true. APA (both ACL and LA) are associated with thromboembolic events. Venous thrombosis is more common than arterial thrombosis and a minority of patients have both. LA is more strongly associated with thrombosis than ACL. The estimated yearly incidence of thrombosis in individuals with APA is 1% for those with no history of thrombosis, 4% for those with SLE, and 6% for those with high titer immunoglobulin G (IgG) ACL. The presence of LA, and possibly of medium to high titers of IgG ACL, help identify patients at risk for thrombosis.     

IgG autoantibodies against beta2-glycoprotein I complexed with a lipid ligand derived from oxidized low-density lipoprotein are associated with arterial thrombosis in antiphospholipid syndrome

We recently reported [J. Lipid Res. 42 (2001), 697; 43 (2002), 1486; 44 (2003), 716] that [beta2-glycoprotein I (beta2GPI) forms complexes with oxidized LDL (oxLDL) and autoantibodies against these complexes are present in patients with SLE and antiphospholipid syndrome (APS). The relationship of beta2GPI/oxLDL complexes and IgG autoantibodies against beta2GPI complexed with oxLig-1 (an oxLDL-derived ligand) with clinical manifestations of APS was studied in 150 APS and SLE patients. The beta2GPI/oxLDL levels of APS patients were similar to those of SLE patients without APS, but they were significantly higher than healthy individuals. There was no difference in the complex levels among the patients with arterial, venous thrombosis, or pregnancy morbidity. IgG anti-beta2GPI/oxLig-1 levels of APS were significantly higher than those of SLE without APS and healthy individuals. Further, antibody levels of APS patients with arterial thrombosis were significantly higher than those patients with venous thrombosis and pregnancy morbidity. Thus, oxidation of LDL leads the complex formation with beta2GPI in SLE and APS patients. In contrast, anti-beta2GPI/oxLig-1 autoantibodies were generated only in APS and were strongly associated with arterial thrombosis. These results suggest that autoantibodies against beta2GPI/oxLDL complexes are etiologically important in the development of atherosclerosis in APS.     

Antiphospholipid syndrome diagnosis: an update

The antiphospholipid syndrome (APS) is characterized by arterial and/or venous thrombosis and pregnancy morbidity in association with the persistent presence of autoantibodies called antiphospholipid antibodies (APAs). APAs are a heterogeneous group of circulating autoantibodies that can be detected either by phospholipid-dependent coagulation test for lupus anticoagulant (LA) or ELISA test for anticardiolipin and anti-β2GPI antibodies. In 2006, the revised criteria for the diagnosis of APS introduce the anti-β2GPI antibodies as a new biological criterion and highlight the necessity to increase the interval between two positive APA test from 6 to 12 weeks. However, despite these updated criteria, the diagnosis of APS remains challenging and we proposed here to make an overview of the latest evolution in the diagnosis of this syndrome.     

Clinical and epidemiological aspects in the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is defined by the occurrence of venous and arterial thromboses, often multiple, and pregnancy morbidity (mainly, recurrent fetal losses and premature births), frequently accompanied by a moderate thrombocytopenia, in the presence of antiphospholipid antibodies (aPL), namely lupus anticoagulant (LA), anticardiolipin antibodies (aCL), or both. Other autoantibodies have also been detected in many patients with an APS, such as anti-beta2 glycoprotein I (GPI), antimitochondrial (M5 type), antiendothelial cell, antiplatelet, antierythrocyte, and antinuclear antibodies. The APS can be found in patients having neither clinical nor laboratory evidence of another definable condition (primary APS) or it may be associated with other diseases. Systemic lupus erythematosus (SLE) is the disorder in which an APS is most commonly associated. Less frequently, aPL and, rarely, an APS may also be encountered in other groups of patients (Table 1) (1).     

Antiphospholipid antibodies and thrombosis: the putative mechanisms of hypercoagulable state in patients with anticardiolipin antibody

Antiphospholipid antibodies are well recognized as associated with serious clinical complications such as arterial and venous thrombosis and recurrent spontaneous abortion. These complications are collectively called antiphospholipid syndrome(APS). The mechanisms responsible for the thrombosis are unclear. We reported three mechanisms. beta 2-glycoprotein I(beta 2GPI) inhibited activated protein C(APC) activity and, furthermore, APC activity decreased by the addition of monoclonal aCL and beta 2GPI. Monoclonal anticardiolipin antibodies(aCL) seemed to enhance the inhibition of APC procoagulant activity caused by beta 2GPI. Monoclonal aCL in the presence of beta 2GPI also increased the activity of plasminogen activator inhibitor(PAI)-1 in the mixture of tissue-plasminogen activator(t-PA) and PAI-1 by inhibiting the function of beta 2GPI, which increased the remaining t-PA activity in the mixture. The formation of thrombin-antithrombin complexes(TAT) in APS was impaired. The level of TAT in APS did not increase, however the level of prothrombin fragment 1 + 2 (F1 + 2) increased. Therefore, free thrombin present in patients' blood may contribute to thrombosis in APS. These reports indicate that thrombosis in APS may be caused by several thrombogenic factors that stimulate aCL.     

Anti-phosphatidylserine/prothrombin antibodies: an additional diagnostic marker for APS?

Among the diagnostic assays for anti-phospholipid syndrome (APS), lupus anticoagulant (LA) is the strongest predictor of thrombosis; however, it presents several limitations as interference with anticoagulant therapy and poor inter-laboratory agreement. Two-thirds of LA activity is apparently due to antibodies against prothrombin (PT), usually detectable by ELISA. Binding of PT to phosphatidylserine (PS) has been shown to enhance solid-phase anti-PT assay sensitivity. To determine the prevalence of antibodies against PS/PT (aPS/PT) in APS, we tested the semiquantitative QUANTA Lite^® aPS/PT ELISA in a cohort of 80 APS patients. The prevalence of aPS/PT was 81.3 %, rising to 87.6 % when considering LA-positive subjects only. We observed a strong correlation between aPS/PT and LA (p = 0.006). To note, APS patients with thrombotic manifestations displayed significantly higher IgG aPS/PT titers compared to 20 aPL asymptomatic carriers (p = 0.012). To rule out a possible cross-reactivity of anti-β2 glycoprotein I antibodies (aβ2GPI) with PS/PT complex, we tested two monoclonal aβ2GPI antibodies and an affinity-purified (AP) polyclonal aβ2GPI IgG obtained from the serum of a patient reacting against both β2GPI and PS/PT. The two monoclonal antibodies did not show any reactivity against PS/PT complex, similarly the AP IgGs did not react toward PS/PT antigen while preserved their aβ2GPI activity. Our findings suggest that aPS/PT are a definite antibody population in APS. Moreover, the good correlation between aPS/PT ELISA and LA may support its use as a surrogate test for LA, particularly useful to overcome the technical limitations of the functional assay.     

Antibodies to age‐β2glycoprotein I in patients with anti‐phospholipid antibody syndrome

Anti‐phospholipid antibody syndrome (APS) is a systemic autoimmune disease characterized clinically by arterial and/or venous thromboses, recurrent abortions or fetal loss and serologically by the presence of ‘anti‐phospholipid antibodies’ (aPL). The main target antigen of the antibodies is β₂glycoprotein I (β₂GPI). Post‐translational oxidative modifications of the protein have been widely described. In this study we aimed to analyse sera reactivity to glucose‐modified β₂GPI (G‐β₂GPI). Sera collected from 43 patients with APS [15 primary APS (PAPS) and 28 APS associated with systemic lupus erythematosus (SLE) (SAPS)], 30 with SLE, 30 with rheumatoid arthritis (RA) and 40 healthy subjects were analysed by an enzyme‐linked immunosorbent assay (ELISA) using a G‐β₂GPI. Nine of 15 consecutive PAPS out‐patients (60%) and 16 of 28 SAPS (57.1%) showed serum antibodies [immunoglobulin (Ig)G class] against G‐β₂GPI (anti‐G‐β₂GPI) by ELISA. The occurrence of anti‐G‐β₂GPI was significantly higher in APS patients compared to patients suffering from SLE. No RA patients or control healthy subjects resulted positive for anti‐G‐β₂GPI. Of note, aG‐β₂GPI prompted to identify some APS patients (four PAPS and seven SAPS), who were negative in the classical anti‐β₂GPI test. Moreover, in APS patients, anti‐G‐β₂GPI titre was associated significantly with venous thrombosis and seizure in APS patients. This study demonstrates that G‐β₂GPI is a target antigen of humoral immune response in patients with APS, suggesting that β₂GPI glycation products may contain additional epitopes for anti‐β₂GPI reactivity. Searching for these antibodies may be useful for evaluating the risk of clinical manifestations.     

Risk of venous and arterial thrombosis according to type of antiphospholipid antibodies in adults without systemic lupus erythematosus: A systematic review and meta-analysis

AimTo evaluate the magnitude of venous and arterial thrombosis risk associated with antiphospholipid antibodies (APLs) in adults without systemic lupus erythematosus (SLE).MethodsCase-control and cohort studies were selected from the MEDLINE and Cochrane Library databases. Two investigators independently extracted data on study design, patient characteristics, venous and arterial events and exposure to APLs, including lupus anticoagulant (LA), anticardiolipin (aCL), anti-β2 Glycoprotein I (β2GpI), anti-prothrombin (aPT), anti-phosphatidyl serine (aPS), and anti-phosphatidyl ethanolamine (aPE).Results30 studies were included (16,441 patients). The odds ratio (OR) for venous thrombosis was 6.14 (95% confidence interval [CI] 2.74–13.8) in LA-positive patients (5 studies, 1650 patients) and 1.46 (CI 1.06–2.03) in aCL‐positive patients (12 studies, 5375 patients). None of the associations with more recently identified APLs was significant, but fewer studies were available. For arterial thrombosis, the OR for LA and aCL was 3.58 (CI 1.29–9.92) and 2.65 (CI 1.75–4.00) respectively. The associations between β2GpI, aPT and aPS and the risk of arterial thrombosis were also significant, the OR being 3.12 (CI 1.51–6.44), 2.95 (CI 1.31–6.66) and 6.00 (CI 3.07–11.7), respectively. Owing to the heterogeneity of cut-off values for each APL assay, we were unable to perform any sensitivity analysis to determine the optimal value. The presence of low-quality studies may have led to overestimation of the magnitude of the associations.ConclusionsLA and aCL were significantly associated with an increased risk of thrombosis, especially arterial, in patients without SLE. Systematic thromboprophylaxis in high-risk patients with APL should be evaluated.     

HLA class II alleles and genetic predisposition to the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by the presence of antiphospholipid antibodies (aPL). Its etiology is linked to genetic predisposition, which is accounted for, at least in part, by genes of major histocompatibility complex (HLA system). The association of APS with human leukocyte antigen (HLA) alleles is a consequence of the association of aPL with HLA alleles. Some HLA alleles carry the risk to produce aPL, and this is independent of the clinical context. In fact, we find the same associations between HLA and aPL in primary APS and in APS secondary to systemic lupus erythematosus (SLE). The association of HLA-DR4, -DR7, -DRw53 and -DQB1*0302 with aCL that has been demonstrated in primary APS can also be found in SLE, a disease with a completely different pattern of HLA allele association (DR2, DR3, DRw52). In addition, the various aPL (anticardiolipin antibodies, lupus anticoagulant, anti-beta2GPI antibodies, antiphosphatidylserine/prothrombin antibodies) show similar HLA association, again independent of the clinical context (primary APS or SLE), and across various ethnic groups.     

Anti-phosphatidylethanolamine antibody,thromboembolic events and the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an acquired disorder characterized by arterial and/or venous thrombosis and pregnancy morbidity. In solid assays, sera from patients with APS usually react to negatively charged phospholipids (PL) and PL cofactors such as β2-glycoprotein I (β2GPI). Binding to neutral PL such as phosphatidylethanolamine (PE) is less common. PE is one of the main lipid components of the biological membranes, being mostly located in the inner leaflet. In 1989 we reported the first case of primary APS whereby a LA was accompanied not by an anticardiolipin antibody (aCL), but by an antibody to PE (aPE).In this review, we update the literature concerning the presence of aPE in patients with thromboembolic events and obstetric morbidity. We also discuss aPE as the sole antibody detected in many of these clinical circumstances. An eventual link of aPE antibodies with failure of in vitro fertilization is also considered as well as uncommon clinical associations of aPE that are also discussed.     

New autoantigens in the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by arterial and venous thrombosis, recurrent miscarriages or fetal loss, and circulating antiphospholipid antibodies (aPL). Enzyme-linked immunosorbent assays for anticardiolipin and anti-β2-glycoprotein I antibodies and clotting assays for the lupus anticoagulant are the tests recommended for detecting aPL. However, the aPL are a heterogeneous group of antibodies directed against anionic phospholipids but also toward phospholipid-binding plasma proteins or phospholipid-protein complexes. β2-glycoprotein I (β2GPI) is the playmaker antigen of APS, however during apoptosis, lysophospholipids can become exposed on the cell surface, and mainly through their interaction with β2GPI, they can become targets of aPL. Some CL metabolites are likely to escape from the remodeling cycle. This would account for the progressive loss of mitochondrial CL during apoptosis, as well as for the presence of CL and lyso-CL at the cell surface, where they can interact with β2GPI and become targets of aPL. Other recognized targets of aPL are represented by phosphatidylserine, lyso(bis)phosphatidic acid, Phosphatidylethanolamine, vimentin, and annexin A5. These molecules may allow improving the knowledge on the pathogenesis, and the early identification of APS. Although several studies have shown the presence of antibodies directed against other antigens in APS, their clinical relevance is still a matter of debate, and it needs to be confirmed with experimental data and longitudinal studies.     

The combination of different antiphospholipid antibody subgroups in the sera of patients with autoimmune diseases is a strong predictor for thrombosis. A retrospective study from a single center

OBJECTITVE: To determine the distribution of different antiphospholipid antibodies (APL-Ab) and their association with thrombosis in patients with autoimmune diseases. METHODS: Clinical data and laboratory features of 30 patients with different autoimmune diseases with positive APL-Ab were retrospectively studied for a period of more than two years. Anti-cardiolipin (aCL), anti-phosphatidylserine (aPS) and anti-beta2-glycoprotein I (abeta2-GPI) antibodies were determined by ELISA. RESULTS: Autoantibodies that target only PS were detected in 53.3% (n = 16) patients, aCL antibodies only were found in one patient (3,3%). In 43.3% (n = 13), aPS were associated with elevated levels of aCL and/or abeta2-GPI antibodies. No thrombotic event occurred in patients with aPS antibodies only compared to 6 patients from the group with different APL-Ab during 808 +/- 92 days of observation. CONCLUSION: The combination of different antiphospholipid antibody subgroups seems to be a predictor for thrombosis. The presence of aPS antibodies without additional aCL or abeta2-GPI is not associated with thrombosis. The measurement of the APL specificities in addition to the aCL antibodies may be important to develop predictive markers for the risk to develop thrombotic events.     

Anti-beta 2-glycoprotein I antibodies of IgM class are linked to thrombotic disorders in young women without autoimmune disease

Antiphospholipid autoantibodies particularly antibodies against beta2-glycoprotein I (anti-beta2GPI) are casually associated with thromboses in patients with autoimmune diseases. However, their exact prevalence and role in the pathogenesis of thromboses in the absence of autoimmune disease is still inconclusive. They might be particularly important when other risk factors of thrombosis are absent. We investigated antiphospholipid antibodies in 68 young women (aged <45yr at onset of the event, without autoimmune disease and with an otherwise low risk of thrombosis) in the stable period following myocardial infarction (MI), lacunar cerebral infarction (LACI) or deep vein thrombosis (DVT) and in 37 healthy age-matched controls. Patients had increased IgM anti-beta2GPI compared to controls (36.0, 11.5-49.5 vs. 17.50, 3.50-30.0 arbitrary units (AU), p<0.001), whereas no difference was obtained in other measured antibodies (anticardiolipin and antiphosphatidylserine (aPS) antibodies of IgG and IgM). IgM anti-beta2GPI positively correlated with some markers of increased coagulation potential and negatively with BMI (r=-039, p<0.005) and other parameters of the metabolic syndrome. In conclusion, we found that levels of IgM anti-beta2GPI are increased in young women suffering arterial or venous thromboses in the absence of other known autoimmune diseases and also in the absence of pronounced classical risk factors. We found that IgM anti-beta2GPI positively correlated with some markers of increased coagulation potential and negatively with parameters of the metabolic syndrome. Thus, it appears that elevated levels of IgM anti-beta2GPI are linked to thrombotic disorders in young women (without autoimmune disease) particularly when classical risk factors or the metabolic syndrome are absent.     

Anti-phospholipid antibodies in HIV infection and SLE with or without anti-phospholipid syndrome: comparisons of phospholipid specificity, avidity and reactivity with beta2-GPI.

Increased prevalence of anti-phospholipid antibodies (aPL) and increased levels of lipid peroxidation have been described in patients with HIV infection. To assess the binding specificity and avidity of aPL antibodies in HIV infection, sera from 44 HIV-1 infected patients were evaluated for antibodies to cardiolipin (aCL), phosphatidyl serine (aPS), phosphatidyl inositol (aPI) and phosphatidyl choline (aPC) using enzyme linked immunosorbent assay (ELISA) methods. Sera from 30 patients with systemic lupus erythematosus (SLE), but without features of anti-phospholipid syndrome (APS) (SLE/non APS), six with SLE and secondary APS, (SLE/APS) and 11 with primary APS (PAPS) were also evaluated as controls. The resistance of the aPL antibody binding to dissociating agents was evaluated by treating the ELISA wells, after serum incubation with 2 M urea or 0.6 M NaCl for 10 min. An anti-beta2-glycoprotein-I (beta2-GPI) ELISA was used to assess serum reactivity against beta2-GPI, a plasma protein considered as the true antigen of aCL antibodies occurring in APS and SLE patients. The prevalence of aCL, aPS, aPI and aPC antibodies in HIV-1 infection was 36%, 56%, 34% and 43% respectively, which was comparable to that found in SLE/APS and PAPS patients and significantly higher than that observed in SLE/non-APS patients. Anti-beta2-GPI antibodies occurred in 5% of HIV-1 infected vs. 17% in SLE/non-APS (P=0.11), 50% in SLE/APS (P=0.009) and 70% in PAPS patients (P=0.0014). A significant decrease of aPL binding after urea and NaCl treatment was observed in the sera of HIV-1-infected, compared to that of APS patients, indicating that aPL antibodies from HIV-1 infected individuals have low resistance to dissociating agents. In conclusion, aPL antibodies (1) occur in HIV-1 infection; (2) tend to recognize various phospholipids but not beta2-GPI; and (3) are of low resistance to dissociating agents-a finding probably reflecting low antibody avidity. Finally, these, like the autoimmune-type aCL antibodies, tend to recognize the oxidized CL-a finding probably indicating autoantibody generation as a result of neoepitope formation by oxidized PLs.     

Can hydroxychloroquine be protective against COVID-19-associated thrombotic events ?

Although SARS-CoV-2 is considered a lung-tropic virus, severe COVID-19 is not just a viral pulmonary infection, clinically it is a multi-organ pathology with major coagulation abnormalities and thromboembolism events. Recently, antiphospholipid (aPL) antibodies were found increased in a large number of COVID-19 patients. Elevated aPL have been well documented in antiphospholipid syndrome (APS), a systemic autoimmune disorder characterized by recurrent venous or arterial thrombosis and/or obstetrical morbidity. Among treatment regimen of APS, hydroxychloroquine (HCQ) is one of the molecules proposed in the primary prevention of thrombosis and obstetrical morbidity in those patients. Due to its antithrombotic properties documented in APS therapy, HCQ could be considered a good candidate for the prevention of thrombotic events in COVID-19 patients in association with anticoagulant and its repurposing deserves further evaluation.     

Does the anti-prothrombin antibodies measurement provide additional information in patients with thrombosis?

The aim of this study is to get new insight into the relevance of IgG anti-prothrombin antibodies in patients with thrombosis and to determine whether human prothrombin alone (aPT) or complexed to phosphatidylserine (aPS/PT) should be preferentially used for measuring these antibodies by enzyme-linked immunosorbent assay (ELISA). To this end, prevalence of anti-prothrombin antibodies, their characteristics in terms of avidity and heterogeneity, and their relationship with anti-beta2 glycoprotein I antibodies (abeta2GPI) were studied in 152 patients with thrombosis. Patients were divided into two groups according to the presence or absence of antiphospholipid antibodies (aPL), called aPL+ or aPL-, respectively. In the aPL- group (n=90), the prevalence of anti-prothrombin antibodies was substantial (10%) but not significantly different from that of control (5%). In the aPL+ group (n=62), lupus anticoagulant (LA) or anticardiolipin antibodies (aCL) positive, 61% were positive for anti-prothrombin antibodies with no statistical difference between aPT and aPS/PT prevalence (42% vs. 55%, respectively). In the whole thrombotic population, 19% were only aPT and 34% only aPS/PT suggesting the presence of different antibodies. Absorption experiments confirmed the heterogeneity of aPT and aPS/PT. No difference in their avidity was demonstrated. From the aPL+ group, 60 were LA positive. Among them, 18% were negative for abeta2GPI and anti-prothrombin antibodies showing that the detection of these antibodies could not substitute for LA determination. In conclusion, our data show that the screening of the different anti-prothrombin antibodies is not warranted in the aPL+ group since these antibodies do not provide additional information compared to aCL, LA and/or abeta2GPI measurement. Nevertheless, the substantial prevalence of anti-prothrombin antibodies in the aPL- group should be further explored in a large prospective study.     

Antiprothrombin antibodies are associated with pregnancy loss in patients with the antiphospholipid syndrome

OBJECTIVE: To document the clinical association between the history of pregnancy loss in patients with the diagnosis of primary or secondary antiphospholipid syndrome (APS) and the presence of different antiprothrombin antibody subtypes [immunoglobulin G (IgG), IgM and IgA] in a cohort of patients with APS. METHODS: Records of 170 female patients with primary APS, or APS secondary to systemic lupus erythematosus (SLE) or secondary to other autoimmune diseases were studied. RESULTS: In female APS patients with IgG antiprothrombin antibodies (n = 105) significant associations to pregnancy loss (p < 0.0001), early pregnancy loss (p < 0.0001) and a negative association to thrombocytopenia (p < 0.01) could be identified. In the group of patients with IgG antiprothrombin antibodies and at least one pregnancy (n = 84) a significant association with pregnancy loss (p < 0.005) and especially with early pregnancy loss (p < 0.0001) was demonstrated. No association with other immunoglobulin subtypes of antiprothrombin antibodies could be documented. In the subgroup of patients with primary APS and at least one pregnancy in the history, pregnancy loss (p < 0.005) and early pregnancy loss (p < 0.0001) were found to be highly associated with the presence of IgG antiprothrombin antibodies. IgG antiprothrombin antibodies represent the highest independent risk factor for pregnancy loss with an odds ratio of 4.5. There was no statistically significant association with venous or arterial thrombosis in all IgG antiprothrombin antibody positive patients. CONCLUSION: The results of this study document the association of IgG antiprothrombin antibodies with pregnancy loss and in particular early pregnancy loss in a large and well-characterized cohort of patients. We would recommend routine testing for antiprothrombin antibodies in young female patients with APS.     

Diagnostic performance of phospholipid-specific assays for the evaluation of antiphospholipid syndrome

The diagnostic performance of commercially available nonstandard antiphospholipid (aPL) assays for the evaluation of antiphospholipid syndrome (APS) is unknown. In 62 patients with APS, 88 with recurrent pregnancy loss, 50 healthy blood donors, and 24 women with one or more successful pregnancies, we measured antiphosphatidic acid (aPA), antiphosphatidyl-choline (aPC), antiphosphatidylethanolamine (aPE), antiphosphatidylglycerol (aPG), antiphosphatidylinositol (aPI), and antiphosphatidyl-serine (aPS) IgG and IgM antibodies from 2 manufacturers. We computed the areas under the curve (AUC), sensitivities, specificities, positive and negative predictive values, and 95% confidence intervals to assess diagnostic performance. The AUC analyses of the IgM assays demonstrated significant differences (P < .01) for all markers except aPC, whereas the IgG markers showed comparable performance for most assays with the exception of aPE (P < .01) and aPS (P = .02) antibodies. Overall, the combined sensitivity of the aPL assays differed significantly between manufacturers and did not improve the diagnostic yield for APS.     

Laboratory evaluation of the antiphospholipid syndrome

The antiphospholipid syndrome (APS) was first described in 1986. The original association of this hypercoagulable state with anticardiolipin antibodies (aCL) resulted from the synthesis of evidence stemming from laboratory findings in systemic lupus erythematosus (SLE), ie, the frequent occurrence of false-positive VDRL tests and the paradoxical observation of the so-called "lupus anticoagulant" (LA), an increase in phospholipid (PL)-dependent clotting times. By the early 1990s, it was clear that a co-factor was involved in the reaction of antibodies to PL (aPL) in SLE patients with secondary APS and that this was a hitherto-obscure protein, beta-2 glycoprotein I (beta2GPI). In the intervening years, it has been established that beta2GPI and other PL-binding proteins such as prothrombin (PT) are relevant antigens in APS and assays for these antigens have been developed, standardized, and applied to subjects with both primary and secondary APS. Measurement and confirmation of LA activity is based on a stepwise approach and should follow the recommendations of the International Society of Thrombosis and Haemostasis. Although antibodies to various PL-binding proteins have been suggested as diagnostic targets for APS, the current (2006) consensus guidelines recognize only LA, aCL, and anti-beta2GPI for the classification of APS.