Ordering Patterns of Thrombophilia Testing and Its Appropriateness

Background Despite society recommendations to limit thrombophilia testing, this testing is often sent inappropriately. The results of thrombophilia testing frequently do not affect management. Additionally, interpretation of thrombophilia testing is confounded by acute thrombosis, anticoagulation (AC) therapy, and other medical comorbidities. Incorrect test selection is also a source of unnecessary testing [i.e. Factor V (FV) activity level instead of Factor V Leiden (FVL)]. The aim of our study was to assess ordering patterns for thrombophilia testing by qualifying the number of tests, identifying the requesting services, and assessing the appropriateness of testing. Methods This was a retrospective study of thrombophilia testing performed at LAC+USC Medical Center, Los Angeles, CA from January 1, 2019 to December 31, 2019. A laboratory query of thrombophilia testing was performed to identify eligible adult patients who received thrombophilia testing without a prior confirmed thrombophilia. Thrombophilia testing included: FVL and prothrombin 20210 gene mutations; activated protein C (APC) resistance; antithrombin, or protein C or S activity levels; and antiphospholipid syndrome (APS) evaluation with lupus anticoagulant, cardiolipin (CL) immunoglobulins IgM/G, and beta-2 glycoprotein (b2gp) IgM/IgG; and JAK2 V617F mutation. Homocysteine (HC) levels and methylenetetrahydrofolate reductase (MTHFR) gene mutation testing were considered to have limited clinical utility. FV activity and phosphatidylserine IgM/IgG were considered incorrect tests. The electronic medical record was reviewed for clinical history, indication for testing, requesting service, and appropriateness. The criteria for defining appropriateness were determined based on major society guidelines and literature review. The main criteria are summarized here. Testing was considered inappropriate for a provoked venous thromboembolism (VTE) or stroke/transient ischemic attack (TIA). For unprovoked VTE, testing was considered inappropriate for patients > 45 yo except for APS testing. For non-stroke arterial thrombosis, recurrent pregnancy loss or stillbirth, and diagnostic evaluation of suspected lupus, APS testing only was considered appropriate. Results 450 patients underwent thrombophilia testing with a mean age of 42 (range: 18-90); 76% were female and 81% were Hispanic. A total of 1698 thrombophilia tests were sent by 27 services. Testing was done in the following settings: inpatient (40%), outpatient (59%), and emergency department (1%). The mean tests per patient were 3.7 (range: 1-12). The most common requesting services were rheumatology (24%), obstetrics-gynecology (19%), and internal medicine/medicine-pediatrics (14%). Hematology requested 10% of tests. Common indications for testing were VTE (21%), rheumatology-related (25%), pregnancy-related (13%), ischemic stroke/TIA (9%), ocular-related (7%), non-stroke arterial thrombosis (3%), and dermatology-related (4%) (Table 1). 5% (84 tests) were sent for the evaluation of other non-thrombotic conditions. 8% (132 tests) were sent for > 1 indication, such as concurrent arterial and venous events. 840 tests (49%) were deemed inappropriate. Common reasons for inappropriate testing included provoked VTE events, stroke/TIA, APS testing after first pregnancy loss, current AC, and duplicate testing (Table 2). APS testing issues included testing for LAC while on AC, incomplete testing (both CL and b2GP not sent), incorrect tests (phosphatidylserine IgM/IgG), and repeat testing < 12 weeks from prior. Incorrect/redundant testing for FVL included: FV activity levels (36 total tests; 9 ordered in additional to FVL and 27 ordered instead of FVL) and APC resistance ordered simultaneously with FVL in 7 patients. Of note, 92 tests were sent for evaluation of non-thrombotic conditions. Conclusions Thrombophilia testing is often done inappropriately. Correct test selection is also a relatively common issue, particularly with APS and FVL testing. Given the large number of services ordering thrombophilia testing at our training hospital and this testing being sent for a variety of reasons, it is unlikely that physician education alone will lead to a substantial or sustained decrease in the number of inappropriate tests. Rather, it may be necessary to restrict at least some thrombophilia testing to certain services. Figure 1 Figure 1. Disclosures Piatek: Rigel: Consultancy, Research Funding; Alexion: Consultancy, Research Funding; Apellis: Research Funding; Dova: Consultancy, Speakers Bureau.

Activated Protein C has a Regulatory Role in Factor VIII Function

Mechanisms thought to regulate activated factor VIII (FVIIIa) cofactor function include A2-domain dissociation and activated protein C (APC) cleavage. Unlike A2-domain dissociation, there is no known phenotype associated with altered APC cleavage of FVIII and biochemical studies suggest APC plays a marginal role in FVIIIa regulation. However, the in vivo contribution of FVIIIa inactivation by APC is unexplored. Here we compared wild-type B-domainless FVIII (FVIII-WT) recombinant protein to an APC resistant FVIII variant (FVIII-R336Q/R562Q; FVIII-QQ). FVIII-QQ demonstrated expected APC resistance without other changes in procoagulant function or A2-domain dissociation. In plasma-based studies, FVIII-WT/FVIIIa-WT demonstrated a dose-dependent sensitivity to APC with or without protein S, while FVIII-QQ/FVIIIa-QQ did not. Importantly, FVIII-QQ demonstrated approximately 5-fold increased procoagulant function relative to FVIII-WT in the tail clip and ferric chloride injury models in hemophilia A (HA) mice. To minimize the contribution of FV inactivation by APC in vivo, the tail clip assay was performed in homozygous HA/FV-Leiden mice infused with FVIII-QQ or FVIII-WT in the presence or absence of mAb1609, an antibody that blocks murine PC/APC hemostatic function. FVIII-QQ again demonstrated enhanced hemostatic function in HA/FV-Leiden mice; however, FVIII-QQ and FVIII-WT performed analogously in the presence of the PC/APC inhibitory antibody, supporting the increased hemostatic effect of FVIII-QQ was APC specific. Our data demonstrate APC contributes to the in vivo regulation of FVIIIa, which has the potential to be exploited to develop novel HA therapeutics.

Influence of DOACs and DOAC Remove® on coagulation assays during thrombophilia testing in DOAC treated patients

Background/Aim. Direct oral anticoagulants (DOACs) administration has a significant interference on coagulation assays. Our study was conducted in order to evaluate the effect of DOACs and DOAC Remove? on coagulation assays during thrombophilia testing. Methods. In the period of January 2019 to the end of June 2020 30 DOAC treated patients tested for thrombophilia, due to venous thromboembolism (VTE), 14 females and 16 males aged 23 to 63 years (median age 47.6 years), were included in the study. Thrombophilia testing was performed using DOAC Remove? tablets (activated charcoal). The results before and after DOAC Remove? were compared. Results. Positive LA results were observed in 20% apixaban, 100% dabigatran, and 70% rivaroxaban treated patient, while in samples after DOAC Remove? the LA positivity was observed only in one from the apixaban group. Before DOAC Remove?, the APC-R ratio was measurable in 40% dabigatran, and 80% rivaroxaban treated patients, while, after using DOAC Remove? the APC-R was measurable in all cases. Comparing the results obtained from the samples before and after DOAC Remove?, a difference was noted in relation to all dRVVT tests, except for the dRVVT ratio in the apixaban group. Clot-based methods for detection of the APC resistance are significantly affected by dabigatran, and less by rivaroxaban. Conclusion. DOAC was practically inactivated after the addition of the DOAC Remove?, which made it possible to perform analyses for the LA and APC-R testing freely and obtain relevant results.

Anti-protein C antibodies and acquired protein C resistance in SLE: novel markers for thromboembolic events and disease activity?

Objectives Risk factors for thromboembolism in SLE are poorly understood. We hypothesized a possible role for protein C, based on its dual activity in inflammation and haemostasis and on the evidence of an association between acquired activated protein C (APC) resistance (APCR) and high-avidity anti-protein C antibodies (anti-PC) with a severe thrombotic phenotype in venous thrombosis APS patients. Methods In a cross-sectional study of 156 SLE patients, the presence and avidity of IgG anti-PC was established by in house-ELISA, and APCR to exogenous recombinant human APC (rhAPC) and Protac (which activates endogenous protein C) was assessed by thrombin generation-based assays. Associations with aPL profile, thrombotic history and disease activity (BILAG and SLEDAI-2K) were also established. Results Anti-PC were detected in 54.5% of patients and APCR in 59%. Anti-PC positivity was associated with APCR to both rhAPC (P <0.0001) and Protac (P =0.0001). High-avidity anti-PC, detected in 26.3% of SLE patients, were associated with APCR in patients with thrombosis only (P <0.05), and with the development of thrombosis over time (range: 0–52 years; P =0.014). High-avidity anti-PC levels correlated with SLEDAI-2K (P =0.033) and total BILAG (P =0.019); SLEDAI-2K correlated inversely with APCR to Protac (P =0.004). Conclusion Anti-PC occur in patients with SLE, independently of aPL profile, and are associated with APCR. High-avidity anti-PC are associated with thrombosis and with active disease and might prove a novel marker to monitor the risk of thrombosis and disease progression in SLE.

Anti–Domain I β2-Glycoprotein I Antibodies and Activated Protein C Resistance Predict Thrombosis in Antiphospholipid Syndrome: TAC(I)T Study

Background Antibodies binding to domain I of β2-glycoprotein I (aDI) and activated protein C (APC) resistance are associated with an increased risk of thrombosis in cross-sectional studies. The objective of this study was to assess their predictive value for future thromboembolic events in patients with antiphospholipid antibodies (aPL) or antiphospholipid syndrome. Methods This prospective multicenter cohort study included consecutive patients with aPL or systemic lupus erythematosus. We followed 137 patients (43.5 ± 15.4 year old; 107 women) for a mean duration of 43.1 ± 20.7 months. Results We detected aDI IgG antibodies by ELISA in 21 patients. An APC sensitivity ratio (APCsr) was determined using a thrombin generation–based test. The APCsr was higher in patients with anti–domain I antibodies demonstrating APC resistance (0.75 ± 0.13 vs 0.48 ± 0.20, P < 0.0001). In univariate analysis, the hazard ratio (HR) for thrombosis over time was higher in patients with aDI IgG (3.31 [95% CI, 1.15–9.52]; P = 0.03) and patients with higher APC resistance (APCsr >95th percentile; HR, 6.07 [95% CI, 1.69–21.87]; P = 0.006). A sensitivity analysis showed an increased risk of higher aDI IgG levels up to HR 5.61 (95% CI, 1.93–16.31; P = 0.01). In multivariate analysis, aDI IgG (HR, 3.90 [95% CI, 1.33–11.46]; P = 0.01) and APC resistance (HR, 4.98 [95% CI, 1.36–18.28]; P = 0.02) remained significant predictors of thrombosis over time. Conclusions Our study shows that novel tests for antibodies recognizing domain I of β2-glycoprotein I and functional tests identifying APC resistance are significant predictors of thrombosis over time and may be useful for risk stratification.

Advances in Understanding Mechanisms of Thrombophilic Disorders

Venous thromboembolism constitutes a major medical problem afflicting millions of individuals worldwide each year. Its pathogenesis is multifactorial, involving both environmental and genetic risk factors. The most common genetic risk factor known to date is a mutation in the factor V (FV) gene (R506Q or FV Leiden), which impairs the normal regulation of FV by activated protein C (APC). APC is an important regulator of blood coagulation, cleaving and inactivating not only FV/FVa but also activated factor VIII (FVIIIa). In FVa, APC cleaves several sites, Arg506 (R506) being one of them. The R506Q mutation results in the APC resistance phenotype and a lifelong hypercoagulable state. A prothrombin gene mutation is another relatively frequent thrombosis risk factor, whereas deficiencies of the anticoagulant proteins antithrombin, protein C, or protein S are less common. As a result of the high prevalence of FV and prothrombin mutations in the general population, combinations of genetic defects are relatively common. Such individuals have highly increased risk of thrombosis.

APC-resistance as a possible predictor of recurrent thrombosis in women with Factor V Leiden

Hypothesis/aims of study. The current analysis was undertaken to elucidate the role of Factor Va resistance to proteolytic cleavage by activated protein C in FVL(1691)GA female carriers in the development of acute and recurrent thromboses. Study design, materials and methods. A prospective clinical cohort study of 1100 women of reproductive age was conducted, with the course and outcomes of 2,707 pregnancies analyzed. Two cohorts were specified: the main group consisted of 500 patients with FV(1691)GA genotype, and the control group consisted of 600 patients with FVL(1691)GG genotype. Results. FVL(1691)GA genotype was significantly associated with the development of venous thromboembolic complications (VTEC) compared to FVL(1691)GG genotype (OR 9.3; p < 0.0001). Episodes of recurrent thrombosis during and outside of pregnancy were registered only in FVL(1691)GA patients (OR 5.7, p = 0.2). In all cases, at the time of the thrombotic event and during the period before the episode of acute or recurrent thrombosis, an APC resistance normalized ratio (NR) value was ≤ 0.49, with no episodes of VTEC registered with an APC resistance NR value ≥ 0.5. Conclusion. Venous thromboses occur under the condition of expressed APC resistance with underlying FVL(1691)GA carriage. The APC resistance index can serve as an objective biochemical marker to determine the feasibility of thromboprophylaxis within the framework of personalized medicine.