Activated protein C resistance assay and factor V Leiden

Comparative analysis of "APTT vs RVVT" based activated protein C resistance assay in the diagnosis of Factor V Leiden mutation

Background

Thrombophilia is a hypercoagulable state characterized by increased venous thrombosis. The most common cause of heritable thrombophilia is Factor V Leiden (FVR506Q) homozygous state, with a relative risk of 10-80 times as compared to normal individuals and Lupus anticoagulant is the most common cause of acquired thrombophilia. The main objective of this study is to compare the sensitivity of activated partial thromboplastin time (APTT) vs dilute Russell viper venom test (DRVVT) based APCR assays with predilution in Factor V-deficient plasma for diagnosis of Factor V Leiden mutation.

Materials And Methods

The coagulometer used for APCR test was Sysmex CS-5100. APTT reagent used is Pathrombin SL supplied by Siemens. All data were expressed as mean ± SD. Statistical analysis was done using unpaired students t-test and a P value <0.05 was considered as statistical significance.

Results

A total of 300 cases of APCR (200 cases of Factor V Leiden mutation was confirmed by PCR and 100 acquired) were studied. The sensitivity of screening APTT-based APCR for detection of Factor V Leiden mutation is 67% and for the noncarrier state, it is 62%. The sensitivity of modified APTT and DRVVT with predilution in FV-deficient plasma for detection of Factor V Leiden mutation is 82% and 84%, respectively and for acquired causes, it is 48% and 86%, respectively.

Conclusion

Screening APTT test has increased in activated protein C resistance (APCR) due to Factor V Leiden mutation as well as acquired causes such as patients on direct-acting oral anticoagulants, warfarin, lupus anticoagulants, and oral contraceptive pills which are independent risk factors of venous thrombosis. Modified DRVVT with predilution in FV-deficient plasma is more sensitive than screening and modified APTT-based APCR test in the diagnosis of Factor V Leiden mutation and the former test can distinguish homozygous and heterozygous states from normal individuals.

Retrospective study of pregnancies in women with Thr331Ala fibrinogen polymorphisms

Background: We aimed to retrospectively review data of pregnant women with the α-fibrinogen Thr331Ala polymorphism; evaluate the relationship between this polymorphism and spontaneous abortion (SA), fetal growth restriction (FGR), and intrauterine fetal death (IUFD); and assess the effects of aspirin and/or heparin.Materials and methods: We examined the outcomes of 29 pregnancies (nine women) in women with the α-fibrinogen Thr331Ala polymorphism. Of these, 16 were untreated, whereas 13 were treated with heparin and/or aspirin.Results: The live birth rate was significantly higher in the treated group than in the nontreated group (69.2 versus 6.2%; p = .0004). In addition, the prophylactic use of a low dose of aspirin and/or heparin during early pregnancy in women with Thr331Ala may be an effective method for reducing fetal loss in these patients.Conclusions: This polymorphism interacts with pregnancy to result in poor obstetrical outcomes, but these effects can be mitigated with medical intervention. This study is the first to report outcomes of pregnancies complicated by the Thr331Ala polymorphism, which we believe may cause thrombophilia, SA, and IUFD. This study highlights the need for further research on this polymorphism in pregnancy.

DOAC-Remove abolishes the effect of direct oral anticoagulants on activated protein C resistance testing in real-life venous thromboembolism patients

Background

Direct oral anticoagulants (DOACs) may cause false results of activated protein C resistance (APC-R) ratio. DOAC-Remove, a new reagent based on activated carbon, has been designed to eliminate the interference of DOACs on coagulation assays. The aim of the study was to investigate whether the use of DOAC-Remove enables to determine APC-R in patients treated with DOACs.

Methods

We assessed 74 venous thromboembolism (VTE) patients, including 25 on rivaroxaban, 25 on apixaban and 24 taking dabigatran. APC-R was determined using the Russell Viper Venom Time (RVVT)-based clotting test. APC-R and DOAC concentrations were tested at baseline and following DOAC-Remove. Thrombophilia, including factor V Leiden (FVL) mutation was tested.

Results

FVL mutation was found in 20 (27%) patients. The APC-R ratio at baseline was measurable in 43 patients (58.1%), including 20 (80%) on rivaroxaban, 19 (76%) on apixaban and four (16.7%) on dabigatran. In patients with measurable APC-R at baseline, the ratio >2.9 was found in 23 patients (53.5%). In 16 (37.2%) subjects APC-R ratio <1.8 suggested FVL mutation which was genetically confirmed. Four (9.3%) FVL carriers on dabigatran showed negative/equivocal APC-R results. In 11 (14.9%) patients taking rivaroxaban or apixaban, in whom blood was collected 2–5 h since the last dose, we observed unmeasurable APC-R. DOAC-Remove almost completely eliminated all plasma DOACs. After addition of DOAC-Remove all APC-R ratios were measurable. In four FVL carriers on dabigatran with false negative APC-R, DOAC-Remove resulted in APC-R ratios <1.8.

Conclusions

DOAC-Remove effectively reduces DOACs concentration in plasma, which enables FVL testing using APC-R.

Activated protein C resistance in patients following venous thromboembolism receiving rivaroxaban versus vitamin K antagonists: assessment using Russell viper venom time-based assay

: Activated protein C resistance (APC-R) is assessed as part of thrombophilia screening, preferably in patients not taking oral anticoagulants. Rivaroxaban is known to alter some APC-R assays. To our knowledge, there have been no reports on the effect of rivaroxaban on the Russell viper venom time (RVVT)-based APC-R assay in real-life patients. In 168 consecutive outpatients suspected of having venous thromboembolism because of thrombophilia, APC-R was determined using the RVVT-based ProC Ac R assay (Siemens, Marburg, Germany). Patients receiving rivaroxaban or vitamin K antagonists were eligible. We measured rivaroxaban concentrations using the anti-Xa Biophen DiXal assay (Hyphen Biomed, Neuville-Sur-Oise, France) and factor V Leiden using the real-time PCR. APC-R was detected in 23 (28%) patients on rivaroxaban (n = 81) administrated 2-48 h since the blood draw, 15 (28%) patients on vitamin K antagonists (n = 54), and in four (12%) patients off anticoagulation (n = 33). Compared with nonanticoagulated patients, APC-R ratios were similar in patients on rivaroxaban, without any correlation with rivaroxaban concentrations (from 0 to 303 μg/l). None of the patients on rivaroxaban were found to have false-negative or false-positive APC-R ratios. Rivaroxaban concentrations up to 300 μg/l do not affect results of the ProC Ac R RVVT-based assay, which could be recommended in patients referred to a clinic for thrombophilia screening in whom the time since the last dose of rivaroxaban is uncertain.

A clinical audit of thrombophilia testing in pediatric patients with acute thromboembolic events: impact on management

Routine testing for inherited and acquired thrombophilia defects is frequently performed in pediatric patients with thromboembolic events (TEEs). No consensus guidelines exist regarding the timing of testing or the type of patients to be tested. The primary objective of our study, therefore, was to determine whether thrombophilia testing during the acute TEE setting affected clinical management in pediatric patients. A secondary aim included estimation of potential harm from thrombophilia testing. We retrospectively reviewed data on all pediatric patients diagnosed with a TEE during a 1-year period. Fifty-two (51%) of 102 patients with a TEE underwent thrombophilia testing during the acute phase, with 26 patients (50%) having a positive test result during the acute phase. Only 12% of patients tested were confirmed to have a thrombophilia eventually, yielding a false-positive rate of ∼7% for testing when performed in the acute setting. There were no changes to the acute management, regardless of a positive or negative result. Testing resulted in unnecessary blood loss in 12 patients younger than 1 year and acute testing cost approximately $82 000. Our data show that thrombophilia testing during acute TEEs in pediatric patients did not impact clinical management. There is also a potential for false-positive tests leading to unnecessary long-term anticoagulation. These findings suggest against thrombophilia testing during acute TEE setting in children.

Diagnostic Testing Approaches for Activated Protein C Resistance and Factor V Leiden: A Comparison of Institutional and National Provider Practices

OBJECTIVES

To analyze the economic impact of testing for activated protein C resistance (APC-R) due to factor V Leiden (FVL) mutation with APC-R with reflexive FVL genotyping (algorithmic approach) or genotyping alone.

METHODS

OptumLabs Data Warehouse (OLDW) data were used to assess testing approaches. Insurance claims for APC-R and FVL in 2013 were compared with the Mayo Clinic database. Centers for Medicare & Medicaid Services diagnostic fee schedules were used to assign costs.

RESULTS

Of 19.3 million OLDW-covered individuals, 74,242 (0.385%) received 75,608 tests: APC-R, 2,265 (2.9%); FVL genotyping, 70,619 (90.1%); and both APC-R and FVL, 2,724 (7.0%). In total, 1,317 tests were performed at Mayo Clinic: APC-R with reflex FVL (1,256; 95.4%) and FVL alone (61; 4.6%). Costs per evaluated individual and per total population (person/year) in OLDW and algorithmic approach were $83.77 vs $36.38 and $0.32 vs $0.14, respectively.

CONCLUSIONS

The cost-optimized algorithmic approach reduces health care costs.

Factor V Leiden

Factor V Leiden (FVLeiden ) is a common hereditary thrombophilia that causes activated protein C (APC) resistance. This review describes many of the most fascinating features of FVLeiden , including background features, mechanisms of hypercoagulability, the founder mutation concept, the "FVLeiden paradox," synergistic interaction with other thrombotic risk factors, the intertwined relationship between FVLeiden and APC resistance testing, and other, uncommon mutations implicated in causing APC resistance. In addition, there are several conditions where laboratory tests for APC resistance and FVLeiden are or can be discrepant, including lupus anticoagulants, anticoagulants such as direct thrombin inhibitors (dabigatran, argatroban, and bivalirudin) and rivaroxaban, as well as pseudohomozygous, pseudo-wildtype, liver transplant, and bone marrow transplant patients. The laboratory test error rate for FVLeiden is also presented.

Activated protein C resistance testing for factor V Leiden

Activated protein C resistance assays can detect factor V Leiden with high accuracy, depending on the method used. Factor Xa inhibitors such as rivaroxaban and direct thrombin inhibitors including dabigatran, argatroban, and bivalirudin can cause falsely normal results. Lupus anticoagulants can cause incorrect results in most current assays. Assays that include dilution into factor V-deficient plasma are needed to avoid interference from factor deficiencies or elevations, which can arise from a wide variety of conditions such as warfarin, liver dysfunction, or pregnancy. The pros and cons of the currently available assays are discussed.