Stroke Thrombectomy and Right Atrial Clot Aspiration in 29 Year Old Woman

We present a case report of a previously healthy 29 year old woman who developed thromboembolic events in rapid fashion after a recent orthopedic surgery. This case highlights the importance of understanding risk factors for clot formation even in those who had no prior events, the efficacy of novel aspiration techniques to remove emboli, and how rapid triaging of acute symptoms can lead to the best outcomes. She presented to the emergency department with shortness of breath and was found to have a large bilateral pulmonary embolus. She was given intravenous thrombolysis. Shortly after, she developed aphasia and right-sided weakness and was taken emergently for mechanical thrombectomy of a left middle cerebral artery occlusion. She was later found to have a patent foramen ovale and a highly mobile right atrial thrombus which was aspirated. Further evaluation revealed right lower extremity peroneal and popliteal deep venous thrombi. She was placed on anticoagulation, made a full clinical recovery, and was discharged home. Prompt recognition of symptoms, efficient in-hospital work flow, and a multidisciplinary approach led to an outstanding outcome in this young patient.

Laboratory Diagnosis of Activated Protein C Resistance and Factor V Leiden

The factor V Leiden (FVL) polymorphism is known as the most common inherited risk factor for venous thrombosis. In turn, FVL is the leading cause of an activated protein C resistance (APCR) phenotype, in which the addition of exogenous activated protein C to plasma does not result in the expected anticoagulant effect. In the routine laboratory approach to the formal diagnosis of FVL, an initial positive screening plasma-based method for APCR is often performed, and only if needed, this is followed by a confirmatory DNA-based assay for FVL. Multiple methods with accepted sensitivity and specificity for determining an APCR/FVL phenotype are commonly categorized into two separate groups: (1) screening plasma-based assays, including qualitative functional clot-based assays, for APCR, and (2) confirmatory DNA-based molecular assays, entailing several tests and platforms, including polymerase chain reaction-based and non-PCR-based techniques, for FVL. This review will describe the methodological aspects of each laboratory test and prepare suggestions on the indication of APCR and FVL testing and method selection.

The methods for removal of direct oral anticoagulants and heparins to improve the monitoring of hemostasis: a narrative literature review

The assessment of hemostasis is necessary to make suitable decisions on the management of patients with thrombotic disorders. In some clinical situations, for example, during thrombophilia screening, the presence of anticoagulants in sample makes diagnosis impossible. Various elimination methods may overcome anticoagulant interference. DOAC-Stop, DOAC-Remove and DOAC Filter are available methods to remove direct oral anticoagulants in diagnostic tests, although there are still reports on their incomplete efficacy in several assays. The new antidotes for direct oral anticoagulants - idarucizumab and andexanet alfa - could be potentially useful, but have their drawbacks. The necessity to remove heparins is also arising as heparin contamination from central venous catheter or therapy with heparin disturbs the appropriate hemostasis assessment. Heparinase and polybrene are already present in commercial reagents but a fully-effective neutralizer is still a challenge for researchers, thus promising candidates remain in the research phase.

Antithrombin Deficiency: Frequency in Patients with Thrombosis and Thrombophilic Families

PURPOSE

Antithrombin (AT) deficiency is a well-known inherited risk factor for venous thromboembolism (VTE). However, F V Leiden and F II20210a mutations have drawn much more attention in the recent years. Therefore, we have decided to analyze the frequency of antithrombin deficiency in different cohorts of patients and tried to formulate indications for its testing.

RESULTS

Antithrombin deficiency was found in 4% of patients with recurrent VTE ≤ 50 years of age with, in 1% of patients with splanchnic vein thrombosis and in 2% of cases associated with combined oral contraceptives (COC) use or pregnancy. In patients with central venous thrombosis, antithrombin deficiency was not found.

RECOMMENDATION

We consider antithrombin testing useful in patients with thrombosis occuring up to 45 years of age without any risk factors. Namely, females with VTE in pregnancy and puerperium should be tested as well as females with thrombosis on COC, if VTE occurred within the first year of their use.

CONCLUSION

In spite of degressive interest in thrombophilia work up, we still consider antithrombin testing useful in defined clinical situations.

Thrombophilia testing in the era of direct oral anticoagulants

Venous thromboembolism (VTE) is increasingly recognised in primary and secondary care practice. The arrival of direct oral anticoagulants (DOACs) has made the management of VTE easier and more convenient. Some patients established on DOACs may need screening for underlying thrombophilias as certain thrombophilic conditions are known to confer a higher thrombosis risk, although the guidelines for when and how to test for a thrombophilia, especially in a patient taking a DOAC, are unclear. This literature review aims to examine when thrombophilia screening should take place in a patient already taking a DOAC, the effect of DOACs on thrombophilia tests, and analyse whether DOACs are safe and effective in both inherited and acquired thrombophilias.

Laboratory testing for activated protein C resistance: rivaroxaban induced interference and a comparative evaluation of andexanet alfa and DOAC Stop to neutralise interference

Background Investigation of hemostasis is problematic when patients are on anticoagulant therapy. Rivaroxaban especially causes substantial interference, extending many clot-based tests, thereby leading to false positive or negative events. In particular, rivaroxaban affects some assays for activated protein C resistance (APCR). Methods We assessed, in an international setting, cross laboratory (n = 31) testing using four samples to evaluate rivaroxaban induced interference in APCR testing, and whether this interference could be neutralised. The samples comprised: (A) pool of normal plasma (APCR-negative control); (B) this normal pool spiked with rivaroxaban (200 ng/mL) to create rivaroxaban-induced interference (potential 'false' positive APCR event sample); (C) the rivaroxaban sample subsequently treated with a commercial direct oral anticoagulant 'DOAC-neutraliser' (DOAC Stop), or (D) treated with andexanet alfa (200 μg/mL). Testing was performed blind to sample type. Results The rivaroxaban-spiked sample generated false positive APCR results for some, but unexpectedly not most APCR-tests. The sample treated with DOAC Stop evidenced a correction in the rivaroxaban-affected APCR assays, and did not otherwise adversely affect the rivaroxaban 'unaffected' APCR assays. The andexanet alfa-treated sample did not evidence correction of the false positive APCR, and instead unexpectedly exacerbated false positive APCR status with many tests. Conclusions DOAC Stop was able to neutralise any APCR interference induced by rivaroxaban. In contrast, andexanet alfa did not negate such interference, and instead unexpectedly created more false-positive APCR events.

A multi-laboratory assessment of congenital thrombophilia assays performed on the ACL TOP 50 family for harmonisation of thrombophilia testing in a large laboratory network

OBJECTIVES

Thrombophilia testing is commonly performed within hemostasis laboratories, and the ACL TOP 50 family of instruments represent a new 'single platform' of hemostasis instrumentation. The study objective was to evaluate these instruments and manufacturer reagents for utility of congenital thrombophilia assays.

METHODS

Comparative evaluations of various congenital thrombophilia assays (protein C [PC], protein S [PS], antithrombin [AT], activated protein C resistance [APCR]) using newly installed ACL TOPs 550 and 750 as well as comparative assessments with existing, predominantly STAGO, instrumentation and reagents. Verification of manufacturer assay normal reference ranges (NRRs).

RESULTS

HemosIL PC and free PS assays showed good comparability with existing Stago methods (R>0.9) and could be considered as verified as fit for purpose. HemosIL AT showed high relative bias with samples from patients on direct anti-Xa agents, compromising utility. Manufacturer NRRs for PC, PS and AT were verified with minor variance. Given the interference with direct anti-Xa agents, an alternate assay (Hyphen) was evaluated for AT, and the NRR also verified. The HemosIL Factor V Leiden (APC Resistance V) evidenced relatively poor performance compared to existing assays, and could not be adopted for use in our network.

CONCLUSIONS

This evaluation of HemosIL reagents on ACL TOP 50 family instruments identified overall acceptable performance of only two (PC, free PS) of four thrombophilia assays, requiring use of third-party reagents on ACL instruments for the other two assays (AT, APCR).

Mixing studies for lupus anticoagulant: mostly yes, sometimes no

Lupus anticoagulants (LAs) represent one manifestation of the clinical condition called antiphospholipid syndrome (APS) and are associated with many adverse clinical outcomes, but primarily with thrombosis and/or pregnancy morbidity. LAs are identified by laboratory testing, principally using clot-based assays based on Russell viper venom time (RVVT) and activated partial thromboplastin time (APTT) test methods. All three of the most recent guidance documents for LA testing recommend using these tests, although they vary in regard to inclusion/exclusion of other test processes. Mixing studies form part of the process of LA identification/exclusion, since in vitro LAs act like coagulation inhibitors. Mixing studies are also supported by all three LA guidance documents, but recommendations vary in regard to relative importance and placement in the LA identification/exclusion algorithm. This Point article takes the position that mixing tests are usually indicated for appropriate identification/exclusion of LAs, but can occasionally be omitted.

The Effect of Direct Oral Anticoagulants on Antithrombin Activity Testing Is Abolished by DOAC-Stop in Venous Thromboembolism Patients

CONTEXT.—

Direct oral anticoagulants (DOACs) may cause false negative results of antithrombin (AT) deficiency screening.

OBJECTIVE.—

To evaluate the impact of DOAC-Stop, an agent reversing in vitro effects of DOACs, on AT testing in anticoagulated patients.

DESIGN.—

We assessed 130 venous thromboembolism patients aged 46.7 ± 13.5 years. Blood samples were collected 2 to 27 hours after DOAC intake from 49 patients on rivaroxaban, 54 on apixaban, and 27 on dabigatran. Antithrombin activity was assessed using the activated factor X (FXa)-based and the activated factor II (FIIa)-based method twice, before and after DOAC-Stop treatment, together with plasma DOAC levels using coagulometric assays.

RESULTS.—

The use of DOAC-Stop did not influence AT activity measured using the FIIa-based assay, whereas there was a marked decrease in AT activity determined using the FXa-based assay (ΔAT = 16.9%; 95% CI, 12.9%-19.1%). The AT-FIIa assay revealed decreased AT level (<79%) in all 10 (7.7%) genetically confirmed AT-deficient patients treated with rivaroxaban or apixaban (n = 5 each), whereas the AT-FXa assay showed decreased AT activity (<83%) in 2 subjects on rivaroxaban and 1 on apixaban with low plasma DOAC concentrations (<90 ng/mL). After DOAC-Stop median AT-FXa activity lowered from 83.5% (interquartile range, 66%-143%) to 65.5% (interquartile range, 57%-75%; P = .005; ΔAT = 18%) in AT-deficient patients, without any false negative results. The ΔAT in the FXa-based assay correlated with rivaroxaban and apixaban concentrations in the AT-deficient patients (r = 0.99, P < .001).

CONCLUSIONS.—

Application of DOAC-Stop enables reliable evaluation of AT deficiency screening in patients taking rivaroxaban or apixaban and tested using the FXa-based method.

Apixaban Does Not Interfere With Protein S or Activated Protein C Resistance (Factor V Leiden) Testing Using aPTT-Based Methods

CONTEXT.—

Apixaban causes a false increase in activated protein C resistance (APCR) ratios and possibly protein S activity.

OBJECTIVE.—

To investigate whether this increase can mask a diagnosis of factor V Leiden (FVL) or protein S deficiency in an actual population of patients undergoing apixaban treatment and hypercoagulation testing.

DESIGN.—

During a 4.5-year period involving 58 patients, we compared the following 4 groups: heterozygous for FVL (FVL-HET)/taking apixaban, wild-type/taking apixaban, heterozygous for FVL/no apixaban, and normal APCR/no apixaban. Patients taking apixaban were also tested for protein S functional activity and free antigen (n = 40).

RESULTS.—

FVL-HET patients taking apixaban had lower APCR ratios than wild-type patients (P < .001). Activated protein C resistance in FVL-HET patients taking apixaban fell more than 3 SD below the cutoff of 2.2 at which the laboratory reflexes FVL DNA testing. No cases of FVL were missed despite apixaban. In contrast to rivaroxaban, apixaban did not interfere with the assessment of protein S activity (mean activity 93.9 IU/dL, free antigen 93.1 IU/dL, P = .39). A total of 3 of 40 patients (8%) had low free protein S antigen (30, 55, and 57 IU/dL), with correspondingly similar activity results (27, 59, and 52 IU/dL, respectively). Apixaban did not cause a missed diagnosis of protein S deficiency.

CONCLUSIONS.—

Despite apixaban treatment, APCR testing can distinguish FVL-HET from healthy patients, rendering indiscriminate FVL DNA testing of all patients on apixaban unnecessary. Apixaban did not affect protein S activity.

Reducing the effect of DOAC interference in laboratory testing for factor VIII and factor IX: A comparative study using DOAC Stop and andexanet alfa to neutralize rivaroxaban effects

INTRODUCTION

Investigation of factors (F) VIII and IX is common, with testing important for diagnosis or exclusion of haemophilia A or B, associated acquired conditions and factor inhibitors. Rivaroxaban, a common direct anti-Xa agent, causes significant interference in clotting assays, including substantial false reduction of factor levels.

AIM

To assess whether rivaroxaban-induced interference of FVIII and FIX testing could be neutralized.

MATERIALS AND METHODS

An international, cross-laboratory exercise for FVIII (n = 84) and FIX (n = 74), using four samples: (A) pool of normal plasma; (B) pool spiked with rivaroxaban (200 ng/mL); (C) rivaroxaban sample subsequently treated with 'DOAC Stop' and; (D) rivaroxaban sample treated with andexanet alfa (200 μg/mL). Testing performed blind to sample type.

RESULTS

All laboratories reported normal FIX and 94% reported normal FVIII in the pool sample. Instead, 55% and 95%, respectively, reported abnormal FIX and FVIII levels for the rivaroxaban sample. DOAC Stop treatment evidenced a correction in most laboratories (100% reported normal FIX and 86% normal FVIII). Andexanet alfa provided intermediate results, with many laboratories still reporting abnormal results (59% for FVIII, 18% for FIX). We also identified reagent-specific issues.

CONCLUSIONS

As expected, rivaroxaban caused false low values of FVIII and FIX. This might lead to increased testing to identify the cause of low factor levels and potentially lead to false identification of (mild) haemophilia A or B if unrecognized by clinicians/laboratories. DOAC Stop effectively neutralized the rivaroxaban effect, but andexanet alfa less so, with reagent-related effects evident, and thus, false low values sometimes persisted.

Coagulation mixing studies: Utility, algorithmic strategies and limitations for lupus anticoagulant testing or follow up of abnormal coagulation tests

Coagulation testing underpins the investigation of hemostasis and/or monitoring of anticoagulation therapy for prevention and/or treatment of thrombosis related pathology. Assessment of coagulation results requires comparison against a normal reference range or interval (NRR/NRI). Results flagged as "abnormal" (ie, above the NRR/NRI for patients not on anticoagulant therapy), typically require further evaluation. eg, follow up or reflexive testing is used to identify the reason for prolongation, especially when supported by clinical context (eg, bleeding). Mixing tests may have utility to help identify the pathway of follow-up testing (ie, towards investigation of factor deficiencies, or else inhibitors), and are also useful for investigation of lupus anticoagulants (LA). In general, mixing tests that "correct" tend to suggest the presence of factor deficiencies, where as those that do not correct suggest the presence of "inhibitors". Various approaches can be used to identify correction/non-correction, and all have strengths and limitations. Furthermore, eventual identification of causal factor deficiencies or even "inhibitors" may (eg, factor VIII or IX deficiencies or inhibitors) or may not (eg, factor XII deficiency) be clinically important. Ultimately, mixing studies performed in view of appropriate clinical scenarios (eg, bleeding patient) and for LA investigations in symptomatic patients will have best utility.

Diagnosis and management of congenital thrombophilia in the era of direct oral anticoagulants

Direct oral anticoagulants (DOAC)s are often preferred to other anticoagulants as they are more practical and do not require routine laboratory monitoring. Less is known about their use in congenital thrombophilia. Efficacy of DOACs in congenital thrombophilia, effect of DOACs and other anticoagulants on diagnostic tests as well as efficacy and safety of anticoagulant use in this population is still a matter of debate. In this review we intended to analyze the potential pitfalls of testing for thrombophilia in patients using DOACs and vitamin K antagonists (VKA)s as well as to suggest strategies to improve diagnostic accuracy in this setting. We also reviewed the literature for evidence regarding the safety and efficacy of DOACs in patients with congenital thrombophilia. Some evidence was found supporting the use of DOACs in low risk thrombophilia, although evidence for their use in high risk thrombophilia is limited to small series and case reports. Our findings support the generation of better evidence to support DOAC use for congenital thrombophilia, especially in the high risk subgroups.

The Russell viper venom time (RVVT) test for investigation of lupus anticoagulant (LA)

Lupus anticoagulants (LAs) are a laboratory representation of the clinical syndrome of antiphospholipid syndrome (APS), and can also arise in other pathological states. Laboratory testing for LA is complex and three separate recent guidelines have been published. One test, the Russell viper venom time (RVVT), is the mandated laboratory test for inclusion in LA identification/exclusion in all three guidance documents. This is because the the RVVT is recognized to have great sensitivity for LA, with this generally recognized to be greater than that of most other LA screening assays. However, the RVVT is also very sensitive to the presence of many anticoagulant drugs, which diminishes its specificity for LA. Various strategies can be used to improve LA specificity and reduce anticoagulant assay interference.