Antiphospholipid syndrome: association between laboratory tests and clinical practice

Functional lupus anticoagulant testing in a large retrospective cohort of thrombosis patients with direct oral anticoagulants

Functional tests for lupus anticoagulants (LA) as part of a thrombophilia workup are commonly performed in patients under anticoagulant therapy that may interfere with assay results. There is no consensus on how these tests should be assessed in patients on direct oral anticoagulants (DOACs). In this retrospective cohort study, we analysed data from patients with a history of thrombosis in whom dilute Russell viper venom time (dRVVT), LA-sensitive aPTT, and solid phase assays for antiphospholipid antibodies (aPL) were performed (n = 3,147, thereof 588 on rivaroxaban, 144 on apixaban, 1,179 on other anticoagulant drugs). The dRVVT ratio was correlated with rivaroxaban (r = 0.30, P < 10^-4) but not with apixaban plasma levels. The LA-sensitive aPTT/aPTT ratio showed no correlation with DOAC levels. Correspondingly, the rate of patients with abnormal dRVVT test was significantly higher (P < 10^-4) under rivaroxaban (88%) than in thrombosis patients without anticoagulant medication (6%), independent from their aPL plasma levels. No isolated positive results of functional LA testing in patients on anticoagulants could be confirmed in repeated testing after discontinuation of the medication (n = 40). These data indicate that rivaroxaban should be discontinued before functional LA testing is performed. However, viable interpretation of these tests appears to be less affected in patients on apixaban.

Anticardiolipin antibody and anti-beta 2 glycoprotein I antibody assays

Antiphospholipid syndrome (APS) is an autoimmune disease and is a risk factor for a number of clinical manifestations; the classic presentations include fetal death or thrombosis (arterial or venous thromboembolism), in the presence of persistently increased titers of antiphospholipid (aPL) antibodies. The actual cause of APS is unknown but thought to be multifactorial. The disease is characterized by the presence of a heterogenous population of autoantibodies against phospholipid-binding proteins. APS presents either in isolation with no evidence of an underlying disease or in concert with an autoimmune disease such as systemic lupus erythematosus or rheumatoid arthritis. The wide diversity in clinical presentation often causes difficulty in identifying and treating patients and therefore a concise laboratory report containing interpretative comments is required to provide needed guidance to the clinician. For a diagnosis of APS to be made both clinical and laboratory classification criteria must be met. Laboratory testing to identify aPL antibodies includes lupus anticoagulant (liquid-based clotting assays) and immunological solid-phase assays (usually enzyme-linked immunosorbent assay formats) for IgG and/or IgM anticardiolipin (aCL) antibodies and anti-beta 2 glycoprotein I (β2-GPI) antibodies. Other autoantibodies, such as those directed against anionic phospholipids, can also be assayed; however they are not of clinical significance. Participation in a quality assurance program and an in-depth technical and clinical understanding of testing for aPL antibodies are required, as methods are limited by poor robustness, reproducibility, specificity, and standardization. Testing is further complicated by the lack of a "gold standard" laboratory test to diagnose or classify a patient as having APS. This chapter discusses the clinical and laboratory theoretical and technical aspects of aCL and anti-β2GPI antibody assays.

Lupus anticoagulants in two children--bleeding due to nonphospholipid-dependent antiprothrombin antibodies

We describe two children with significant bleeding: one with multiple ecchymoses and the other with scrotal bleeding. In both patients, the activated partial thromboplastin time (APTT) was prolonged, with positivity for lupus anticoagulants (LA). However, the Owren prothrombin time (PT), usually insensitive for LA, was also prolonged. The presence of LA is associated with diverse clinical manifestations, with most patients being asymptomatic while others present venous or arterial thrombosis. Bleeding in conjunction with LA is rare and it is unusual to see prolongation of the Owren PT assay due to LA. An extended laboratory investigation of one of the patient's plasma revealed not only LA but also a specific nonphospholipid-dependent antiprothrombin antibody causing an acquired hypoprothrombinemia.

CONCLUSION

It is likely that the low prothrombin activity and not the LA caused the bleeding. The bleeding signs and symptoms in both patients subsided when the PT was normalized, although the prolonged APTT and the LA remained.

beta2-glycoprotein i is a cofactor for tissue plasminogen activator-mediated plasminogen activation

OBJECTIVE

Regulation of the conversion of plasminogen to plasmin by tissue plasminogen activator (tPA) is critical in the control of fibrin deposition. While several plasminogen activators have been described, soluble plasma cofactors that stimulate fibrinolysis have not been characterized. The purpose of this study was to investigate the effects of beta(2)-glycoprotein I (beta(2)GPI), an abundant plasma glycoprotein, on tPA-mediated plasminogen activation.

METHODS

The effect of beta(2)GPI on tPA-mediated activation of plasminogen was assessed using amidolytic assays, a fibrin gel, and plasma clots. Binding of beta(2)GPI to tPA and plasminogen was determined in parallel. The effects of IgG fractions and anti-beta(2)GPI antibodies from patients with antiphospholipid syndrome (APS) on tPA-mediated plasminogen activation were also measured.

RESULTS

Beta(2)-glycoprotein I stimulated tPA-dependent plasminogen activation in the fluid phase and within a fibrin gel. The beta(2)GPI region responsible for stimulating tPA activity was shown to be at least partly contained within beta(2)GPI domain V. In addition, beta(2)GPI bound tPA with high affinity (K(d) approximately 20 nM), stimulated tPA amidolytic activity, and caused an overall 20-fold increase in the catalytic efficiency (K(cat)/K(m)) of tPA-mediated conversion of Glu-plasminogen to plasmin. Moreover, depletion of beta(2)GPI from plasma led to diminished rates of clot lysis, with restoration of normal lysis rates following beta(2)GPI repletion. Stimulation of tPA-mediated plasminogen activity by beta(2)GPI was inhibited by monoclonal anti-beta(2)GPI antibodies as well as by anti-beta(2)GPI antibodies from patients with APS.

CONCLUSION

These findings suggest that beta(2)GPI may be an endogenous regulator of fibrinolysis. Impairment of beta(2)GPI-stimulated fibrinolysis by anti-beta(2)GPI antibodies may contribute to the development of thrombosis in patients with APS.

Laboratory Evaluation of Antiphospholipid Antibodies in Patients With Venous Thromboembolism

The objective of our study was to evaluate the significance of extended antiphospholipid profile in patients with venous thromboembolism without any systemic autoimmune disease. In 140 patients (age 18-69 years; 47.1% men) with venous thromboembolism and 136 control participants we tested anticardiolipin antibodies, anti-beta 2 glycoprotein I (anti-β2-GPI) and also non-criteria antiphospholipid antibodies: antiphosphatidic acid, antiphosphatidylethanolamine, antiphosphatidylglycerol, antiphosphatidylinositol, antiphosphatidylserine. Commercial and in-house enzyme-linked immunosorbent assays were used. The antibodies with significantly higher prevalence in patients (compared to controls) were: immunoglobulin (Ig) M-anticardiolipin antibodies (12.9%; P = 0.035), IgG-anti-β2-GPI (16.4%; P = 0.0032), IgM-antiphosphatidylethanolamine (14.3%; P = 0.014). In most cases, these three antibodies did not overlap. In conclusion, of non-criteria antiphospholipid antibodies, only antiphosphatidylethanolamine were significantly more prevalent in patients with venous thromboembolism, with only minor overlapping with the criteria antiphospholipid antibodies. Our results suggest the possible utility of searching for antiphosphatidylethanolamine in the clinical suspicion of antiphospholipid syndrome and the absence of criteria antiphospholipid antibodies.

The enigmas of the lupus anticoagulant: mechanisms, diagnosis, and management

Lupus anticoagulant (LA) is a laboratory abnormality associated with the antiphospholipid syndrome. It is a paradoxical phenomenon in which one or more in vitro diagnostic clotting tests are prolonged and thus seem due to an anticoagulant, whereas the antiphospholipid syndrome is manifest clinically as inappropriate or excessive thrombosis. LA should be suspected when thrombosis, recurrent fetal loss, or a prolonged phospholipid (PL)-dependent clotting test is present without other identifiable causes. Despite the heterogeneity of LA antibodies, a consensus has evolved to identify the LA. Four conditions must be met for this laboratory diagnosis: 1) prolongation of a PL-based clotting test, 2) confirmation of an inhibitor-like pattern in the clotting test, 3) confirmation of PL dependence in coagulation tests, and 4) exclusion of a specific factor inhibitor. Even with an extensive armamentarium for LA diagnosis and treatment, it is still a formidable task.

Anti-prothrombin antibodies predict thrombosis in patients with systemic lupus erythematosus: a 15-year longitudinal study

OBJECTIVE

To evaluate the role of anti-prothrombin (anti-PT) antibodies in predicting thrombosis in patients with systemic lupus erythematosus (SLE).

METHODS

An inception cohort of 101 SLE patients (12 males, 89 females; mean age 30 +/- 8 years), was considered. Clinical and laboratory evaluations were regularly performed during a 15-year follow-up (median 108 months) with a special focus on thromboembolic events. Serum samples were collected at time of diagnosis and at least once a year thereafter. IgG and IgM anti-PT, anti-cardiolipin (aCL) and anti-beta(2)glycoprotein I (beta(2)GPI) antibodies were measured by enzyme-linked immunosorbent assay (ELISA); lupus anticoagulant (LAC) was assayed by the dilute Russell's viper venom time and activated partial thromboplastin time tests. The analytical specificity of anti-PT ELISA was investigated. The timing of thrombosis occurrence was calculated using the Kaplan-Meier method.

RESULTS

In the 15-year follow-up, thrombosis occurred in 14 out of the 101 patients: venous thrombosis in nine cases and arterial thrombosis in five. IgG and/or IgM anti-PT, anti-beta(2)GPI and aCL antibodies, and LAC activity were detected in ten, nine, seven, and nine cases, with sensitivity for thrombosis of 71.4%, 64.3%, 50% and 64.3%, respectively. Thrombosis-free survival was 90% at 5 years and 85.8% at 10 and 15 years, respectively. Thrombosis was predicted by anti-PT (P = 0.001), anti-beta(2)GPI antibodies (P = 0.002) and LAC activity (P = 0.001). Moreover, the risk of thrombosis progressively increased with the number of positive antiphospholipid antibody tests. The presence of four positive antibody tests was associated with a risk of thrombosis thirtyfold higher than in their absence.

CONCLUSIONS

This longitudinal study shows that IgG anti-PT antibodies are predictors of thrombosis in SLE patients.

Factores relacionados con el riesgo de trombosis en pacientes con lupus y positividad para anticuerpos antifosfolipídicos

BACKGROUND AND OBJECTIVE

Antiphospholipid antibodies (aPL) are frequently associated with eritematosus systemic lupus (SLE) and increases the risk of thrombosis. The aim of the study was to analize risk factors of thrombosis and its temporal profile in subjects with SLE.

PATIENTS AND METHOD

One hundred and two SLE patients -mean age: 37.5 years (range: 8-85); 90 women; mean of follow-up: 72 months (range: 9-324); 41 (40.2%) with aPL positive- were included in the study. Actuarial Kaplan-Meier curves were used to assess the thrombosis risk and Cox proportional hazard model was used to evaluate factors associated with the risk.

RESULTS

13 thrombotic events occurred in the group with aPL positive (mean of follow up: 83.5 months) and 5 events in aPL negative group (mean of follow up: 72 months). The event-rates were 3.93 and 0.96/100 patients/year for each group, respectively. Survival curves showed a significantly higher risk of thrombotic events in the patients with positive aPL as compared to the aPL negative group, and the risk still present throughout the observational time. Activated partial thromboplastine time up to 37 s was significantly associated with thrombosis risk (p = 0.003). Furthermore, positivity of lupus anticoagulant and proteinuria > 2.5 g/day tended to increase thrombotic risk, although they did not achieve statistical significance.

CONCLUSIONS

In patients with SLE and aPL, risk of first thrombosis remains over the years, and a large activated partial thromboplastine time was the most important risk factor.

Autoantibodies against the fibrinolytic receptor, annexin 2, in antiphospholipid syndrome

The association of thrombosis and gestational morbidity with antiphospholipid antibodies is termed antiphospholipid syndrome (APS). Annexin 2 (A2) is a profibrinolytic endothelial cell surface receptor that binds plasminogen, its tissue activator (tPA), and beta(2)-glycoprotein I (beta2GPI), the main antigen for antiphospholipid antibodies. Here, we evaluate A2 as a target antigen in APS. Serum samples from 434 individuals (206 patients with systemic lupus erythematosus without thrombosis, 62 with APS, 21 with nonautoimmune thrombosis, and 145 healthy individuals) were analyzed by enzyme-linked immunosorbent assay (ELISA) and immunoblot for antiphospholipid and A2 antibodies. Anti-A2 antibodies (titer > 3 SDs) were significantly more prevalent in patients with APS (22.6%; venous, 17.5%; arterial, 34.3%; and mixed thrombosis, 40.4%) than in healthy individuals (2.1%, P < .001), patients with nonautoimmune thrombosis (0%, P = .017), or patients with lupus without thrombosis (6.3%, P < .001). Anti-A2 IgG enhanced the expression of tissue factor on endothelial cells (6.4-fold +/- 0.13-fold SE), blocked A2-supported plasmin generation in a tPA-dependent generation assay (19%-71%) independently of beta2GPI, and inhibited cell surface plasmin generation on human umbilical vein endothelial cells (HUVECs) by 34% to 83%. We propose that anti-A2 antibodies contribute to the prothrombotic diathesis in antiphospholipid syndrome.

Prolonged aPTT after kidney transplantation due to transient lupus anticoagulants

BACKGROUND

After kidney transplantation, a renal biopsy may be needed to elucidate the reasons for lack of graft function. If the activated partial thromboplastin time (aPTT) is prolonged, the biopsy will often be postponed, as increased risk of bleeding must be expected. However, aPTT prolongation is not always due to lack of coagulation factors, but can be due to the presence of lupus anticoagulants (LAs). Clinical observations in our department indicated that a large proportion of recently kidney-transplanted patients developed prolonged aPTT values without clinical complications.

METHODS

A prospective study of patients receiving a kidney transplant in 2004 was conducted to investigate the frequency and cause of prolongation of the aPTT.

RESULTS

Twenty-seven patients were included in the study; none had prolonged aPTT or LAs before the transplantation. In the post-transplantation period, 19 patients (70.4%) had a significantly prolonged aPTT. Further investigation showed that for all 19 patients, prolongation was due to acquired antibodies: 13 had developed LAs and six had developed unspecific antibodies. The acquired antibodies were transient and did not affect clinical outcome.

CONCLUSIONS

This is the first study investigating prolonged aPTT in the post-transplantation period. All patients with prolonged aPTT had acquired transient antibodies, i.e. LA or 'LA-like'. If a renal biopsy was requested, 70.4% of the transplanted patients would presumably have their biopsy postponed due to prolonged aPTT, but as LAs do not increase the risk of bleeding, such a delay would be unnecessary. Immediate LA investigation is therefore recommended if a recently transplanted patient requiring surgical procedures has a prolonged aPTT.

The antiphospholipid syndrome

Antiphospholipid syndrome is an autoimmune disorder characterized by the association between antiphospholipid antibodies and venous or arterial thrombosis or obstetric complications. In spite of the recent progresses, many aspects of this disease remain unclear. In this review, we briefly focus on the most important advances in the pathophysiology, diagnosis and treatment of this condition.

Síndrome antifosfolípide

Condição adquirida, sistêmica, caracterizada por tromboses recorrentes no sistema arterial, venoso ou ambos, a síndrome antifosfolípide pode ser primária ou secundária, esta última mais associada ao lúpus eritematoso sistêmico e menos freqüentemente a infecções, fármacos e outras doenças. São marcadores sorológicos da síndrome antifosfolípide os anticorpos antifosfolípides anticoagulante lúpico e anticardiolipina. O critério diagnóstico primário inclui trombose arterial ou venosa e morte fetal recorrente. Cerca de 41% dos pacientes apresentam lesões cutâneas como primeiro sinal da síndrome, que também pode provocar livedo reticular, ulcerações cutâneas, vasculite livedóide, entre outras manifestações. Seu controle consiste principalmente no tratamento e profilaxia da trombose com anticoagulantes e antiagregantes plaquetários.