Evaluation of four coagulation tests to detect plasma lupus anticoagulants

Lupus Anticoagulant Detection under the Magnifying Glass

Diagnosis of antiphospholipid syndrome (APS) requires the presence of a clinical criterion (thrombosis and/or pregnancy morbidity), combined with persistently circulating antiphospholipid antibodies (aPL). Lupus anticoagulant (LA) is one of the three laboratory parameters (the others being antibodies to either cardiolipin or β2-glycoprotein I) that defines this rare but potentially devastating condition. For the search for aCL and aβ2-GP-I, traditionally measured with immunological solid-phase assays (ELISA), several different assays and detection techniques are currently available, thus making these tests relatively reliable and widespread. On the other hand, LA detection is based on functional coagulation procedures that are characterized by poor standardization, difficulties in interpreting the results, and interference by several drugs commonly used in the clinical settings in which LA search is appropriate. This article aims to review the current state of the art and the challenges that clinicians and laboratories incur in the detection of LA.

Testing for Lupus Anticoagulants

Lupus anticoagulant (LA) is one of the three criteria antiphospholipid antibodies (aPLs) employed in classification, and by default diagnosis, of antiphospholipid syndrome (APS). Detection of LA is not via calibrated assays but is based on functional behavior of the antibodies in a medley of coagulation assays. A prolonged clotting time in a screening test is followed by demonstration of phospholipid dependence and inhibitory properties in confirmatory and mixing tests, respectively, which are modifications of the parent screening test. Complications arise because no single screening test is sensitive to every LA, and no test is specific for LA, because they are prone to interference by other causes of elevated clotting times. Several screening tests are available but the pairing of dilute Russell's viper venom time (dRVVT) with LA-sensitive activated partial thromboplastin time (aPTT) is widely used and recommended because it is proven to have good detection rates. Nonetheless, judicious use of other assays can improve diagnostic performance, such as dilute prothrombin time to find LA unreactive with dRVVT and aPTT, and the recently validated Taipan snake venom time with ecarin time confirmatory test that are unaffected by vitamin K antagonist and direct factor Xa inhibitor anticoagulation. Expert body guidelines and their updates have improved harmonization of laboratory practices, although some issues continue to attract debate, such as the place of mixing tests in the medley hierarchy, and areas of data manipulation such as assay cut-offs and ratio generation. This article reviews current practices and challenges in the laboratory detection of LA.

The Antiphospholipid Thrombosis Syndromes: A Common Multidisciplinary Medical Problem

Antiphospholipid antibodies are increasingly being identified as a cause of arterial and venous thrombosis as well as fetal wastage syndrome via placental vascular thrombosis. The antiphospholipid thrombosis syndromes should be considered and searched for when suggestive clinical findings are present or when unexplained arterial or venous thrombosis occurs. Noting the presence and type of antiphospholipid antibody thrombosis syndrome assumes major importance with respect to not only making an accurate diagnosis of cause of thrombosis but also in selecting effective antithrombotic therapy. The antiphospholipid thrombosis syndromes and the thrombotic and other clinical manifestations span almost all medical specialities and should be construed as a truly multidisciptinary medical problem. Key Words: Thrombosis-Anticardiolipin antibody—Lupus anticoagulant.

Cost-effectiveness of testing for hypercoagulability and effects on treatment strategies in patients with deep vein thrombosis

PURPOSE

Among patients with deep vein thrombosis, hypercoagulable conditions impart a substantial risk of recurrent thrombosis. We sought to determine the cost-effectiveness of testing for these disorders, as well as which tests should be selected and how results should be used.

METHODS

Using a Markov state-transition model, strategies of testing or not testing for a hypercoagulable state followed by anticoagulation for 6 to 36 months were compared in a hypothetical cohort of patients with apparently idiopathic deep vein thrombosis who were followed for life. Strategies were compared based on lifetime costs, quality-adjusted life-years (QALYs), and marginal cost-effectiveness.

RESULTS

In the base case, testing followed by 24 months of anticoagulation in patients with a hypercoagulable condition was more cost-effective ($54,820; 23.76 QALYs) than usual care, which comprised 6 months of anticoagulation without testing ($55,260; 23.72 QALYs). All hypercoagulable conditions tested were common enough and associated with a sufficient risk of recurrence to justify inclusion in a test panel. Twenty-four months of initial anticoagulation was preferred (<$50,000/QALY) for most conditions, whereas lifetime anticoagulation was preferred for patients with antiphospholipid antibody syndrome ($2928/QALY) or homozygous factor V Leiden mutation ($3804/QALY). Models using newer evidence on recurrence suggested 18 to 36 months of anticoagulation without testing as the preferred approach.

CONCLUSION

Testing for hypercoagulable disorders in patients with idiopathic deep vein thrombosis followed by 2 years of anticoagulation in affected patients is cost-effective. A simpler approach of treating all patients with prolonged anticoagulation without testing is justified if data confirm the persistent risk of recurrent thrombosis.

Antiphospholipid thrombosis syndromes

Antiphospholipid antibodies are strongly associated with thrombosis and are the most common of the acquired blood protein defects causing thrombosis. Although the precise mechanism(s) whereby antiphospholipid antibodies alter hemostasis to induce a hypercoagutable state remain unclear, numerous theories, as previously discussed, have been advanced. The most common thrombotic events associated with anticardiolipin antibodies are deep vein thrombosis and pulmonary embolus (type I syndrome), coronary or peripheral artery thrombosis (type II syndrome), or cerebrovascular/retinal vessel thrombosis (type II syndrome); occasionally, patients present with mixtures of these types (type IV syndrome). Type V patients are those with antiphospholipid antibodies and RMS. It is as yet unclear how many seemingly normal individuals who may never develop manifestations of antiphospholipid syndrome (type VI) harbor asymptomatic antiphospholipid antibodies. The relative frequency of anticardiolipin antibodies in association with arterial and venous thrombosis strongly suggests that these should be looked for in any individual with unexplained thrombosis; all three idiotypes (IgG, IgA, and IgM) should be assessed. Also, the type of syndrome (I through VI) should be defined if possible, as this may dictate both type and duration of both immediate and long-term anticoagulant therapy. Unlike those with anticardiolipin antibodies, patients with primary lupus anticoagulant thrombosis syndrome usually experience venous thrombosis. Because the aPTT is unreliable inpatients with lupus anticoagulant (prolonged in only about 40 to 50% of patients) and is not usually prolonged in patients with anticardiolipin antibodies, definitive tests, including ELISA for anticardiolipin antibodies, the dRVVT for lupus anticoagulant, hexagonal phospholipid neutralization procedure, and beta-2-GP-I (IgG, IgA, and IgM) should be immediately ordered when suspecting antiphospholipid syndrome or in individuals with otherwise unexplained thrombotic or thromboembolic events. If results of these tests are negative, in the appropriate clinical setting, subgroups should also be assessed. Finally, most patients with antiphospholipid thrombosis syndrome will fail warfarin therapy and, except for retinal vascular thrombosis, may fail some types of antiplatelet therapy; thus it is of major importance to make this diagnosis so that patients can be treated with the most effective therapy for secondary prevention--LMWH or UH in most instances, and clopidogrel in some instances.

Acquired haemophilia - a study of ten cases

Clinico-haematological features in 10 patients with acquired Haemophilia are presented. Three patients had FVIII inhibitors following pregnancy while in six the cause for development of inhibitors could not be determined. One patient had acquired von Willebrand's disease. Lupus anticoagulant coexisted with Factor VIII inhibitors in three patients. All patients presented with sudden onset of bleeding without any past or family history of a bleeding disorder. Factor VIII inhibitor levels ranged from 8 to 512 Bethesda units in the nine patients. Immunosuppressive therapy was given to 8 patients, consisting of CVP regimen or corticosteroids with endoxan or cyclosporin. Seven patients had clinical and laboratory responses and one patient did not respond. One patient had severe postpartum bleeding with acute shock which was controlled with FEIBA. Diagnosis and management of idiopathic acquired Haemophilia, thus, continues to be a major challenge, and among acquired Haemophilia, postpartum Haemophilia has good prognosis.

New Method for Quantifying Lupus Anticoagulant

A method is presented using a new reagent containing propylgallate for the quantitative determina tion of lupus anticoagulant. The amount of an optimized phospholipid standard required by the clotting reaction was found to be 32-50 μg/ml at a 95% confidence level, with a mean of 41 μg/ml. This method eliminates the ef fect of heparin therapy, coumadin therapy, factor-VIII inhibitor, factor-IX inhibitor, and single-factor deficien cies that afflict presently used lupus anticoagulant screen ing and confirmatory procedures. Using this method, it should be possible to detect lupus anticoagulant in pa tients at a much lower level and follow the effect of ther apy on lupus anticoagulant.

Antiphospholipid antibody syndrome: an unusual cause of stroke in a 22-year-old female

A 22-year-old female presented to the Emergency Department after the acute onset of left hemiparesis. Marked prolongation of the partial thromboplastin time, mild thrombocytopenia, a history of syphilis, and recent spontaneous abortion suggested the diagnosis of antiphospholipid antibody syndrome, an unusual cause of ischemic stroke. This case illustrates the clinical and laboratory features of this uncommon disorder.