Clinical Investigation of Hereditary and Acquired Thrombophilic Factors in Patients with Venous and Arterial Thromboembolism

Background

The clinical relevance of thrombophilic laboratory factors, especially the "mild" ones, and the need for their screening is not generally recommended in venous (VTE) and/or arterial (ATE) thromboembolism.

Methods

Our aim was to investigate possible associations between comorbidities and 16 inherited/acquired "severe" and "mild" laboratory thrombophilic factors (detailed in introduction) in patients (n=348) with VTE/ATE without a serious trigger (high-risk surgical intervention, active cancer and/or chemo-radiotherapy). Cases with VTE/ATE were enrolled when the thrombotic event occurred under the age of 40, in case of positive family history, recurrent thromboembolism, idiopathic event or unusual location. Patients without a detailed thrombophilia screening or who suffered from both ATE/VTE were excluded to find potential distinct thrombosis type specific thrombophilic risks. The possible role of "mild" factor accumulation was also investigated in VTE (n=266).

Results

Elevation of factor VIII clotting activity was associated with VTE rather than ATE. Varicose veins together with postthrombotic syndrome were strongly related to several "mild" factors. Besides "severe" we found that the "mild" thrombophilic factors were also strongly associated with VTE/ATE. Comorbidities/conditions such as diabetes and smoking were generally associated with hyperlipidemia; moreover, both had a correlation with lipoprotein (a) in VTE. We also revealed an important contribution of "mild" factors in increasing trends of several types and localizations of VTE.

Conclusion

In summary, besides the "severe" thrombophilic factors, the "mild" ones also seem to play a non-negligible role in the manifestation of thrombosis, especially in combination. Therefore, an extended screening might be useful in the personalized recommendation of antithrombotic prophylaxis.

EDTA-Induced Pseudothrombocytopenia up to 9 Months after Initial COVID-19 Infection Associated with Persistent Anti-SARS-CoV-2 IgM/IgG Seropositivity

Platelets have a role in vascular complications of COVID-19-related viral coagulopathy. Although immune-induced thrombocytopenia has been described mostly in moderate-to-severe COVID-19, the prognostic role of platelet count in COVID-19 is still controversial. Pseudothrombocytopenia has been reported to represent COVID-19-associated coagulopathy in critical illness, and transient EDTA-dependent pseudothrombocytopenia lasting less than 3 weeks was described in a patient with severe acute COVID-19 pneumonia. In our case study, EDTA-induced pseudothrombocytopenia was still present at 9 months after an initial SARS-CoV-2 virus infection in an apparently recovered 60 year old man. The persistence of antinucleocapside and antispike antibodies 9 months after the initial infection suggests that EDTA-induced pseudothrombocytopenia may be related to anti-SARS-CoV-2 IgG or IgM antibodies. We should acknowledge the possibility that pseudothrombocytopenia may also appear in some patients after seroconversion after the launch of large-scale vaccination programs.

Laboratory Approaches to Test the Function of Antiphospholipid Antibodies

Antiphospholipid syndrome (APS) is a systemic autoimmune disorder caused by the presence of aPLs (antiphospholipid antibodies, i.e., anti-β₂-glycoprotein I and anti-cardiolipin). Everyday practice in terms of laboratory diagnostics of APS includes determination of aPLs and well-known functional assays assessing for lupus anticoagulant (LA), in turn using various tests. According to recent guidelines, the recommended method for LA identification or exclusion is based on the Russell Viper Venom test and a sensitive activated partial thromboplastin time assay. Despite the fact that LA can be quantified in laboratory practice in this way, LA is still used as a binary parameter that is just one of the risk factors of thrombosis in APS. As of today, there are no other functional assays to routinely assess the risk of thrombosis in APS. It is well-known that APS patients display a wide range of clinical outcomes although they may express very similar laboratory findings. One way to solve this dilemma, could be if antibodies could be further delineated using more advanced functional tests. Therefore, we review the diagnostic approaches to test the function of aPLs. We further discuss how thrombin generation assays, and rotational thromboelastometry tests can be influenced by LA, and how experimental methods, such as flow cytometric platelet activation, surface plasmon resonance, or nano differential scanning fluorimetry can bring us closer to the puzzling interaction of aPLs with platelets as well as with their soluble protein ligand. These novel approaches may eventually enable better characterization of aPL, and also provide a better linkage to APS pathophysiology.

A novel homozygous mutation (1619delC) in GPIIb gene associated with Glanzmann thrombasthenia, the decay of GPIIb-mRNA and the synthesis of a truncated GPIIb unable to form complex with GPIIIa

The absence of agonist-induced platelet aggregation and the lack of fibrinogen receptor (GPIIb/IIIa) on the platelet surface demonstrated that the severe hemorrhagic complications of a child of Romany descent were caused by Glanzmann thrombasthenia. DNA sequencing revealed a novel homozygous deletion of a cytosine (1619delC) in the GPIIb gene causing a frameshift and predicting a novel stop codon at position 533 following 24 altered amino acids. Both parents possessed the same deletion in heterozygous form. The amount of GPIIb mRNA in the patient’s platelets was 0.06% of the amount measured in control platelets. Neither GPIIb nor its truncated form could be detected in the platelets of the patient by Western blotting, while a small amount of GPIIIa was demonstrated. Quantitative flow cytometric analysis showed an elevated number of vitronectin receptors, a component of which is GPIIIa, on the patient’s platelets. The surface expression of vitronectin receptor on thrombasthenic, but not on normal platelets was further increased by activation with thrombin receptor agonist peptide. BHK cells transfected with wild type GPIIIa and mutated GPIIb failed to express any mature GPIIb or pro-GPIIb. Immunoprecipitation with a polyclonal antibody recognizing both GPIIb and GPIIIa recovered a 60 kDa truncated form of GPIIb. This band was absent when immunoprecipitation was carried out with an antibody recognizing GPIIIa, suggesting that the truncated protein, lacking calf-1, calf-2 domains and major part of the thigh domain, is unable to form complex with GPIIIa.

Assessment of Factor XIII

Blood coagulation factor XIII (FXIII) is essential for maintaining hemostasis. The absence of FXIII results in severe bleeding diathesis, which without prophylaxis frequently leads to fatal bleeding. As the usual hemostasis screening tests remain normal, the diagnosis of FXIII deficiency needs specific tests. Here, we describe FXIII activity determination by the ammonia release assay, which is the first-line test in the diagnostic algorithm for FXIII deficiency. The method for another activity test, the undeservedly rarely used fibrin cross-linking assay, is also presented. Further tests used for the classification of FXIII deficiencies, measurement of FXIII activity in platelets, ELISAs for the measurement of complex plasma FXIII (FXIII-A₂B₂) antigen and for FXIII-A₂ in plasma and platelets are also included. Detailed description of the methods for the detection and measurement of neutralizing auto- and alloantibodies is also provided.

Neutralizing autoantibody against factor XIII A subunit resulted in severe bleeding diathesis with a fatal outcome - characterization of the antibody

Essentials Autoantibody against factor XIII (FXIII) is a rare but severe acquired hemorrhagic diathesis. In an elderly patient, anti-FXIII-A antibody led to severe bleedings with fatal outcome. The neutralizing autoantibody bound to FXIII with high affinity (Ka≈10(9) m(-1) ). The dominant effect of the autoantibody was the inhibition of activated FXIII.

SUMMARY

Autoantibodies may develop against the catalytic A subunit of factor XIII (FXIII-A) or the carrier B subunit (FXIII-B). Autoimmune FXIII-A deficiency was diagnosed in an elderly (75 years) patient with severe bleeding symptoms. The patient had 3% FXIII activity, and unmeasurable FXIII-A2 B2 and FXIII-A antigens in the plasma, whereas, in the platelet lysate, activity and FXIII-A antigen values were normal. As revealed by western blotting, FXIII antigen was present in the plasma, but the autoantibody interfered with the immunoassays. A mixing study indicated the presence of inhibitor with a titer of 63.2 Bethesda units (BU). The patient's IgG bound to FXIII-A2 B2 and to FXIII-A2 with equally high affinity (Ka in the range of 10(9) m(-1) ). It exerted a multiple inhibitory effect on FXIII activation/activity (IC50: 50 μg mL(-1) ). Immunosupressive therapy gradually decreased the autoantibody titer to 8.0 BU, but FXIII activity remained very low, and, owing to recurrent bleeding, the patient died.

Antiphospholipid antibodies in acute coronary syndrome

Antiphospholipid (aPL) antibodies entailing anticardiolipin (aCL) and anti-β2 glycoprotein I (anti-β2 GPI) antibodies may be involved in a number of vascular diseases including coronary artery diseases (CAD) or stroke. Here we assessed the presence of aPL antibodies in acute coronary syndrome (ACS). The frequency of anti-β2 GPI antibodies was significantly higher (14.4%) in ACS in comparison to control healthy subjects (2%). In addition, serum concentrations of anti-β2 GPI antibodies were also increased in ACS. Anti-β2 GPI antibodies of the IgA isotype might be the most relevant for the onset and outcome of ACS. Regarding subclasses of ACS, anti-β2 GPI IgA antibodies were elevated in unstable angina (UA) and myocardial infarction with ST elevation (STEMI), but not in myocardial infarction without ST elevation (NSTEMI). The involvement of anti-β2 GPI antibodies in ACS was more pronounced in men than women, and in younger rather than older patients. Finally, anti-β2 GPI antibodies in ACS were associated with previous stroke, but not with hypertension or previous myocardial infarction. Thus, anti-β2 GPI antibodies may be involved in the thrombotic events underlying ACS.

Evaluation of flow cytometric HIT assays in relation to an IgG-Specific immunoassay and clinical outcome

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a severe side effect of heparin treatment caused by platelet activating IgG antibodies generated against the platelet factor 4 (PF4)-heparin complex. Thrombocytopenia and thrombosis are the leading clinical symptoms of HIT.

METHODS

The clinical pretest probability of HIT was evaluated by the 4T score system. Laboratory testing of HIT was performed by immunological detection of antibodies against PF4-heparin complex (EIA) and two functional assays. Heparin-dependent activation of donor platelets by patient plasma was detected by flow cytometry. Increased binding of Annexin-V to platelets and elevated number of platelet-derived microparticles (PMP) were the indicators of platelet activation.

RESULTS

EIA for IgG isotype HIT antibodies was performed in 405 suspected HIT patients. Based on negative EIA results, HIT was excluded in 365 (90%) of cases. In 40 patients with positive EIA test result functional tests were performed. Platelet activating antibodies were detected in 17 cases by Annexin V binding. PMP count analysis provided nearly identical results. The probability of a positive flow cytometric assay result was higher in patients with elevated antibody titer. 71% of patients with positive EIA and functional assay had thrombosis.

CONCLUSIONS

EIA is an important first line laboratory test in the diagnosis of HIT; however, HIT must be confirmed by a functional test. Annexin V binding and PMP assays using flow cytometry are functional HIT tests convenient in a clinical diagnostic laboratory. The positive results of functional assays may predict the onset of thrombosis. © 2016 International Clinical Cytometry Society.

Integrity(®) bare-metal coronary stent-induced platelet and endothelial cell activation results in a higher risk of restenosis compared to Xience(®) everolimus-eluting stents in stable angina patients

Drug-eluting stenting (DES) has become a reliable tool for coronary stenting; however, its direct effects on platelet and endothelium function differ from those of bare-metal stenting (BMS). This study involved a periprocedural analysis of various biomarkers of cellular activation after elective DES (Xience(®), Abbott Vascular, Santa Clara, CA, USA) or BMS (Integrity(®), Medtronic, Minneapolis, MI, USA). Forty-nine stable angina patients were recruited: 28 underwent BMS, and 21 received everolimus-eluting stents. Samples were collected (i) prior to stenting, (ii) at 24 hours after procedure, and (iii) after 1 month of dual antiplatelet therapy. Platelet activation was analyzed by surface P-selectin positivity in parallel with plasma levels of soluble P-selectin, CD40L and platelet-derived growth factor (PDGF). Endothelial cell (EC) activation was detected by measuring markers of early (von Willebrand factor) and delayed response (VCAM-1, ICAM-1, E-selectin). Patients were followed for 6 months for the occurrence of restenosis or stent thrombosis. Increased platelet activation was sustained regardless of stent type or antiplatelet medication. Concentrations of most EC markers were more elevated after BMS than after DES. No stent thrombosis was seen, but six BMS subjects displayed restenosis with significantly higher sCD40L (779 [397-899] vs. 381 [229-498] pg/mL; p = 0.032) and sICAM-1 (222 [181-272] vs. 162 [153-223] ng/mL; p = 0.046) levels than in those without complication, while DES patients exhibited significantly decreased PDGF (572 [428-626] vs. 244 [228-311] pg/mL; p = 0.004) after 1 month. Nonresponsiveness to antiplatelet drugs did not influence these changes. In conclusion, the degree of platelet and EC activation suggests that Xience(®) DES may be regarded a safer coronary intervention than Integrity(®) BMS, with a lower risk of in-stent restenosis.

Progressive chromogenic anti-factor Xa assay and its use in the classification of antithrombin deficiencies

BACKGROUND

Antithrombin (AT) is a slow-acting progressive inhibitor of activated clotting factors, particularly thrombin and activated factor X (FXa). However, the presence of heparin or heparan sulfate accelerates its effect by several magnitudes. AT deficiency, a severe thrombophilia, is classified as type I (quantitative) and type II (qualitative) deficiency. In the latter case mutations may influence the reactive site, the heparin binding-site (HBS) and exert pleiotropic effect. Heterozygous type II-HBS deficiency is a less severe thrombophilia than other heterozygous subtypes. However, as opposed to other subtypes, it also exists in homozygous form which represents a very high risk of venous thromboembolism.

METHODS

A modified anti-FXa chromogenic AT assay was developed which determines both the progressive (p) and the heparin cofactor (hc) activities, in parallel. The method was evaluated and reference intervals were established. The usefulness of the assay in detecting type II-HBS AT deficiency was tested on 78 AT deficient patients including 51 type II-HBS heterozygotes and 18 homozygotes.

RESULTS

Both p-anti-FXa and hc-anti-FXa assays showed excellent reproducibility and were not influenced by high concentrations of triglyceride, bilirubin and hemoglobin. Reference intervals for p-anti-FXa and hc-anti-FXa AT activities were 84%-117% and 81%-117%, respectively. Type II-HBS deficient patients demonstrated low (heterozygotes) or very low (homozygotes) hc-anti-FXa activity with normal or slightly decreased p-anti-FXa activity. The p/hc ratio clearly distinguished wild type controls, type II-HBS heterozygotes and homozygotes.

CONCLUSIONS

Concomitant determination of p-anti-FXa and hc-anti-FXa activities provides a reliable, clinically important diagnosis of type II-HBS AT deficiency and distinguishes between homozygotes and heterozygotes.

Pneumatic tube system for transport of laboratory samples: preanalytical aspects

Introduction: A considerable proportion of laboratory errors occurs in the preanalytical phase. Aim: The aims of the authors were to study preanalytical errors in routine and emergency laboratory diagnostics in a regional clinical laboratory and evaluate the effect of the pneumatic tube system on turnaround time and laboratory results. Method: The ratio of preanalytical errors and reasons of test rejection were analysed. In addition, the effects of pneumatic tube and manual transport on the occurrence of hemolysis and platelet activation were compared. Results: Using the pneumatic tube transport system, preanalytical error was below 1%. The main causes of test rejection were haemolysis in case of serum samples, and clot formation and citrate excess in anticoagulated samples. The pneumatic tube transport resulted in significantly faster sample transport, more equalized sample arrival and processing, hence the turnaround time became shorter both for routine and emergency tests. Conclusions: Autovalidation and proper control of preanalytical errors are essential for rapid and reliable laboratory service supported by the pneumatic tube system for sample transport. Orv. Hetil., 2014, 155(28), 1113–1120.

The superiority of anti-FXa assay over anti-FIIa assay in detecting heparin-binding site antithrombin deficiency

OBJECTIVES

Antithrombin is a progressive inhibitor of active factor X (FXa) and thrombin (FIIa). Its effect is 500- to 1,000-fold accelerated by heparin or heparan sulfate. Heterozygous type I (quantitative) and most type II (qualitative) antithrombin deficiencies highly increase the risk of venous thromboembolism (VTE), while homozygous mutations are lethal. The functional defect affecting the heparin-binding site confers moderate risk of VTE to heterozygous and high risk of VTE to homozygous individuals.

METHODS

Antithrombin activity assays based on the inhibition of FIIa and FXa were compared for their efficiency in detecting heparin-binding site defects.

RESULTS

With a single exception, in heterozygotes for heparin-binding site defects (n = 20), anti-FIIa activities remained in the reference interval, while anti-FXa activities were uniformly decreased. In individuals who were homozygous for heparin-binding site mutations (n = 9), anti-FIIa activities were in the range of 48% to 80%; the range of anti-FXa activities was 9% to 25%. Anti-FIIa and anti-FXa activities in type I deficiencies and type II pleiotropic deficiency did not differ significantly.

CONCLUSIONS

Anti-FXa antithrombin assay is recommended as a first-line test to detect type II heparin-binding site antithrombin deficiency.

[Activity of natural coagulation inhibitor proteins in the acute phase of ischaemic stroke]

INTRODUCTION

Decreased activity of natural anticoagulants (antithrombin-lll, protein C, protein S) rarely causes cerebral ischaemia, however it can be found frequently in acute phase of ischaemic stroke. The authors' aim was to investigate whether the decreased activity of natural anticoagulants is accompanied by worsening of symptoms in ischaemic stroke.

PATIENTS AND METHOD

Sixty-eight acute ischaemic stroke patients were investigated. Severity of symptoms were assessed and followed by the NIH Stroke Scale. Antithrombin-Ill, protein C, protein S activities, and concentration of C-reactive protein (CRP) were measured within 48 hours after onset of ischaemic stroke.

RESULTS

Progressing stroke was found in 29% of patients. Decreased activity of at least one natural anticoagulant proteins was present in 31% of patients. Progression of stroke symptoms occurred in 76% of patients with decreased natural anticoagulant activity, while this proportion was only 9% in those with normal natural coagulation inhibitor protein activity (p < 0.01). Progressing stroke was also more frequent in patients with elevated CRP value (60%) than in those with normal CRP level (11%; p < 0.05). Decreased activity of natural anticoagulants was more frequent in patients with elevated CRP concentration compared with patients with normal CRP.

CONCLUSION

The results demonstrate the importance of decreased activity of natural anticoagulants in acute phase of ischaemic stroke. This abnormality was present in about 1/3 of stroke patients. The decreased activity of natural coagulant inhibitor proteins may play an important role in development of progressing stroke thus indicating unfavourable outcome.

[High-shear force-induced platelet aggregation in the screening and diagnosis of von Willebrand disease]

Von Willebrand's disease (vWD) is the most common congenital haemorrhagic diathesis, characterized by the quantitative or qualitative disorder of von Willebrand factor (vWF). A number of methods have been used for the diagnosis of the disease, and the bleeding time determination is widely accepted as a screening test in spite of its low sensitivity. Our aim was to evaluate and compare the performance of two high shear systems (the O'Brien filter test and the PFA-100 device) in the screening and diagnosis of vWD. Thirty patients (n = 13 type 1 with mild symptoms, n = 9 type 1 with severe symptoms, n = 2 type 2A, n = 3 type 2B and n = 3 type 3 vWD) and twenty controls were investigated. In mild vWD the platelet retention in the second phase of the filter test with citrated blood showed the highest sensitivity (91.6%). The sensitivity of the PFA-100 method with collagen-epinephrine cartridges in this group was 76.9%, while the bleeding time was prolonged only in 15.4% of the cases. In severe type 1, in type 2A and type 3 all functional tests reflected the bleeding tendency of the patients. In type 2B disease the bleeding time was prolonged only when the patient was thrombocytopenic, but both high shear systems revealed the disease independently of the presence of thrombocytopenia. The overall sensitivity of the bleeding time determination was 50% compared to the 80-90% sensitivity of the O'Brien filter test and the PFA-100 system. The sensitivity values of the filter test and the PFA-100 device with collagen-epinephrine cartridges were in the same range, but the collagen-ADP cartridges showed a lower (65.5%) sensitivity, though the results were specific and had high positive predictive value. We conclude that both high shear systems are suitable for the screening of vWD, and that they are superior to the traditional bleeding time determination in case of mild disease or type 2B vWD.

Postocclusion hyperemia in the isolated fibrillating blood-perfused dog heart

Reactive hyperemia following occlusions of 15, 30, 60 and 120 sec duration was studied in the left coronary vascular bed of the isolated fibrillating dog heart perfused with arterial blood at constant pressure or constant volume. Except for repayment, linear correlations were found between occlusion time and the characteristics of reactive hyperemia. At a basal perfusion pressure of 50 mm Hg the postocclusion reaction was absent. The maximum hyperemic response was observed at 100 mm Hg, while on a further increase of perfusion pressure reactive hyperemia decreased. The postocclusion reaction was more marked but of briefer duration under constant pressure perfusion. The results can be explained by the joint effects of metabolic, myogenic, and physical factors on coronary vascular tone.

Regulation of myocardial oxygen consumption by perfusion pressure in isolated fibrillating canine heart

In order to evaluate whether perfusion pressure or coronary flow affect myocardial oxygen metabolism, oxygen consumption of the isolated fibrillating blood-perfused canine heart was investigated at perfusion pressures of 100, 150, and 200 mm Hg. To obtain different coronary flow rates at a given coronary perfusion pressure, alpha-adrenergic blockade by phenoxybenzamine (10 mg/kg b.w.) was applied, resulting in an increase in coronary flow and a decrease in myocardial oxygen extration. Myocardial oxygen consumption was increased by elevation of perfusion pressure in both the control and phenoxybenzamine-pretreated group. At the same level of perfusion pressure there was no significant difference between the oxygen consumption of control and phenoxybenzamine-pretreated preparations. It can be concluded that in the isolated fibrillating canine heart oxygen consumption is primarily regulated by perfusion pressure, and is independent from coronary blood flow.