Interpretation and Validation of Maximum Absorbance Data Obtained from Turbidimetry Analysis of Plasma Clots

HIV infection and ART use are associated with altered plasma clot characteristics in Black South Africans

BACKGROUND

Human immunodeficiency virus (HIV) and antiretroviral treatment (ART) are both associated with hypercoagulability. Altered clot properties could be a potential mechanism thereof. We aimed to investigate the association of HIV and ART, with fibrinogen and plasma clot properties in a group of Black South Africans.

METHODS

At baseline, 151 newly diagnosed people living with HIV (PLWH) and 176 controls were recruited. Some PLWH subsequently commenced with ARTs (n = 70) while others remained ART-naïve (n = 81). Fibrinogen and clot properties (turbidity assay) were investigated from baseline to 5-year follow-up. A sub-group of 21 women (n = 10 ART-treated; n = 11 ART-naïve) with HIV was systematically selected and matched with 12 controls, and additional clot properties (rheometry, permeability and fibre diameter) were investigated.

RESULTS

Fibrinogen was lower in the HIV groups compared to the controls, while % γ' fibrinogen was higher. PLWH had shorter lag times and lower maximum absorbance than the controls (p<0.05). Their CLTs on the other hand were longer. Most variables increased over time in all groups, but differences in the degree of change over time was observed for lag time (p = 0.024) and permeability (p = 0.03). Participants who commenced with ART had a tendency of delayed clot formation (p = 0.08) and increased clot permeability (p = 0.005).

CONCLUSION

PLWH had lower total fibrinogen concentration and formed less dense clots. They also formed clots that were more difficult to lyse, which likely not resulted from altered clot properties. ART use (NNRTI's) had a moderately protective effect, delaying clot formation, and increasing clot permeability.

Reprograming Clots for In Vivo Chemical Targeting in Traumatic Brain Injury

Traumatic brain injury (TBI) is a critical public health concern, yet there are no therapeutics available to improve long-term outcomes. Drug delivery to TBI remains a challenge due to the blood-brain barrier and increased intracranial pressure. In this work, a chemical targeting approach to improve delivery of materials to the injured brain, is developed. It is hypothesized that the provisional fibrin matrix can be harnessed as an injury-specific scaffold that can be targeted by materials via click chemistry. To accomplish this, the brain clot is engineered in situ by delivering fibrinogen modified with strained cyclooctyne (SCO) moieties, which incorporated into the injury lesion and is retained there for days. Improved intra-injury capture and retention of diverse, clickable azide-materials including a small molecule azide-dye, 40 kDa azide-PEG nanomaterial, and a therapeutic azide-protein in multiple dosing regimens is subsequently observed. To demonstrate therapeutic translation of this approach, a reduction in reactive oxygen species levels in the injured brain after delivery of the antioxidant catalase, is achieved. Further, colocalization between azide and SCO-fibrinogen is specific to the brain over off-target organs. Taken together, a chemical targeting strategy leveraging endogenous clot formation is established which can be applied to improve therapeutic delivery after TBI.

Effect of prothrombin Belgrade mutation, causing antithrombin resistance, on fibrin clot properties

INTRODUCTION

Prothrombin Belgrade mutation is the result of the c.1787G>A substitution in the prothrombin gene. It is located in the antithrombin and sodium binding site and leads to impaired inactivation of thrombin by antithrombin, resulting in antithrombin resistance and thrombotic disorders. However, it negatively affects sodium binding and may have hypocoagulant effects. Considering that prothrombin Belgrade mutation mechanism is still not fully elucidated and that sodium binding is important for thrombin affinity towards fibrinogen, our aim was to determine whether this mutation affects fibrin clot formation and lysis.

METHODS

Using HEK293T cell line, recombinant wild type and mutated prothrombin were generated by transient transfection. Samples that correspond to plasma of a non-carrier, heterozygous and homozygous carriers were reconstituted using prothrombin deficient plasma and recombinant proteins. Reconstituted samples were used in OHP assay (Overall Hemostasis Potential) to determine kinetic profiles of coagulation and fibrinolysis. Clot turbidity assay was performed to observe kinetics of clot formation and lysis more closely. Fibrin clots formed in reconstituted plasma samples were analyzed by confocal microscopy to determine density of fibrin network. Fibrin clots were additionally observed using electron microscopy to determine thickness of individual fibrin fibers.

RESULTS

No significant difference found in OHP, OCP, OFP, and fibrin network density between wild type, heterozygous, and homozygous carrier reconstituted plasma samples. There were significant differences between samples for slope and slope time parameters in kinetic profiles and fibrin fiber thickness.

CONCLUSIONS

Results indicate that prothrombin Belgrade mutation has no significant impact on fibrinolysis, however it may affect kinetics of clot formation and its architecture.

International council for standardisation in haematology recommendations on fibrinogen assays, thrombin clotting time and related tests in the investigation of bleeding disorders

This guidance was prepared on behalf of the International Council for Standardisation in Haematology (ICSH) by an international working group of clinicians and scientists. The document focuses on tests and assays used for the assessment of fibrinogen function, particularly in the scenario of bleeding disorders. Thrombin clotting time (TT) is used as a screening test in some laboratories and also has some utility when direct anticoagulants are in use. The Clauss fibrinogen assay remains the method of choice for the assessment of fibrinogen function, but there are some situations where the results may be misleading. Prothrombin time derived fibrinogen assays are frequently used, but should be interpreted with caution; the results are not interchangeable between different methods and fibrinogen can be overestimated in certain clinical scenarios. Viscoelastic point of care methods may be helpful in emergency situations, while Reptilase time (and similar tests) are useful combined with TT in distinguishing heparin contamination of samples (i.e., if an incorrect blood draw is suspected) and the presence of direct thrombin inhibitors. Fibrinogen antigen assays should be used in the investigation of functional fibrinogen abnormalities; fibrinogen antigen and genetic testing are recommended in the confirmation of congenital fibrinogen disorders. The following recommendations for fibrinogen function assessment are based on published literature and expert opinion and should supplement local regulations and standards.

Fibrin clot properties in cardiovascular disease: from basic mechanisms to clinical practice

Fibrinogen conversion into insoluble fibrin and the formation of a stable clot is the final step of the coagulation cascade. Fibrin clot porosity and its susceptibility to plasmin-mediated lysis are the key fibrin measures, describing the properties of clots prepared ex vivo from citrated plasma. Cardiovascular disease (CVD), referring to coronary heart disease, heart failure, stroke, and hypertension, has been shown to be associated with the formation of dense fibrin networks that are relatively resistant to lysis. Denser fibrin mesh characterized acute patients at the onset of myocardial infarction or ischaemic stroke, while hypofibrinolysis has been identified as a persistent fibrin feature in patients following thrombotic events or in those with stable coronary artery disease. Traditional cardiovascular risk factors, such as smoking, diabetes mellitus, hyperlipidaemia, obesity, and hypertension, have also been linked with unfavourably altered fibrin clot properties, while some lifestyle modifications and pharmacological treatment, in particular statins and anticoagulants, may improve fibrin structure and function. Prospective studies have suggested that prothrombotic fibrin clot phenotype can predict cardiovascular events in short- and long-term follow-ups. Mutations and splice variants of the fibrinogen molecule that have been proved to be associated with thrombophilia or increased cardiovascular risk, along with fibrinogen post-translational modifications, prothrombotic state, inflammation, platelet activation, and neutrophil extracellular traps formation, contribute also to prothrombotic fibrin clot phenotype. Moreover, about 500 clot-bound proteins have been identified within plasma fibrin clots, including fibronectin, α2-antiplasmin, factor XIII, complement component C3, and histidine-rich glycoprotein. This review summarizes the current knowledge on the mechanisms underlying unfavourable fibrin clot properties and their implications in CVD and its thrombo-embolic manifestations.

Physiological correction of hereditary mild hypofibrinogenemia during pregnancy

INTRODUCTION

Hereditary hypofibrinogenemia is a rare fibrinogen disorder characterised by decreased levels of fibrinogen. Pregnant women with hypofibrinogenemia are at risk of adverse obstetrical outcomes, depending on the fibrinogen level.

AIM

We investigated how the physiological changes of hemostasis throughout the pregnancy impact the hemostatic balance in a woman with hereditary mild hypofibrinogenemia.

METHODS

Fibrin clot properties were analyzed by turbidimetry and scanning electron microscopy, clot weight and red blood cells retention were measured by whole clot contraction, and in vitro thrombin generation was assessed by calibrated automated thrombogram and ex vivo by TAT.

RESULTS

Throughout the pregnancy, the fibrinogen levels increased reaching normal values in the third trimester (activity 3.1 g/L, antigen 3.2 g/L). In parallel, the fibrin polymerisation increased, the fibrinolysis decreased, the fibrin clot network became denser with thicker fibrin fibers, and the fibrin clot weight and red blood cells retention increased, reaching control's value at the third trimester. Similarly, in vitro and ex vitro thrombin generation increased, reaching maximum values at the delivery.

CONCLUSION

In this case of hereditary mild hypofibrinogenemia we observed a physiological increase of fibrinogen and thrombin generation. Future studies should focus on moderate and severe hypofibrinogenemia, to assess fibrinogen variation and the overall impact of increased TG on the hemostasis balance.

Mechanisms for Reduced Fibrin Clot Formation on Liquid-Infused Surfaces

Biomedical devices are prone to blood clot formation (thrombosis), and liquid-infused surfaces (LIS) are effective in reducing the thrombotic response. However, the mechanisms that underpin this performance, and in particular the role of the lubricant, are not well understood. In this work, it is investigated whether the mechanism of LIS action is related to i) inhibition of factor XII (FXII) activation and the contact pathway; ii) reduced fibrin density of clots formed on surfaces; iii) increased mobility of proteins or cells on the surface due to the interfacial flow of the lubricant. The chosen LIS is covalently tethered, nanostructured layers of perfluorocarbons, infused with thin films of medical-grade perfluorodecalin (tethered-liquid perfluorocarbon), prepared with chemical vapor deposition previously optimized to retain lubricant under flow. Results show that in the absence of external flow, interfacial mobility is inherently higher at the liquid-blood interface, making it a key contributor to the low thrombogenicity of LIS, as FXII activity and fibrin density are equivalent at the interface. The findings of this study advance the understanding of the anti-thrombotic behavior of LIS-coated biomedical devices for future coating design. More broadly, enhanced interfacial mobility may be an important, underexplored mechanism for the anti-fouling behavior of surface coatings.

The Applicability of Current Turbidimetric Approaches for Analyzing Fibrin Fibers and Other Filamentous Networks

Turbidimetry is an experimental technique often used to study the structure of filamentous networks. To extract structural properties such as filament diameter from turbidimetric data, simplifications to light scattering theory must be employed. In this work, we evaluate the applicability of three commonly utilized turbidimetric analysis approaches, each using slightly different simplifications. We make a specific application towards analyzing fibrin fibers, which form the structural scaffold of blood clots, but the results are generalizable. Numerical simulations were utilized to assess the applicability of each approach across a range of fiber lengths and diameters. Simulation results indicated that all three turbidimetric approaches commonly underestimate fiber diameter, and that the “Carr-Hermans” approach, utilizing wavelengths in the range of 500−800 nm, provided <10% error for the largest number of diameter/length combinations. These theoretical results were confirmed, under select conditions, via the comparison of fiber diameters extracted from experimental turbidimetric data, with diameters obtained using super-resolution microscopy.

Automated Fiber Diameter and Porosity Measurements of Plasma Clots in Scanning Electron Microscopy Images

Scanning Electron Microscopy (SEM) is a powerful, high-resolution imaging technique widely used to analyze the structure of fibrin networks. Currently, structural features, such as fiber diameter, length, density, and porosity, are mostly analyzed manually, which is tedious and may introduce user bias. A reliable, automated structural image analysis method would mitigate these drawbacks. We evaluated the performance of DiameterJ (an ImageJ plug-in) for analyzing fibrin fiber diameter by comparing automated DiameterJ outputs with manual diameter measurements in four SEM data sets with different imaging parameters. We also investigated correlations between biophysical fibrin clot properties and diameter, and between clot permeability and DiameterJ-determined clot porosity. Several of the 24 DiameterJ algorithms returned diameter values that highly correlated with and closely matched the values of the manual measurements. However, optimal performance was dependent on the pixel size of the images—best results were obtained for images with a pixel size of 8–10 nm (13–16 pixels/fiber). Larger or smaller pixels resulted in an over- or underestimation of diameter values, respectively. The correlation between clot permeability and DiameterJ-determined clot porosity was modest, likely because it is difficult to establish the correct image depth of field in this analysis. In conclusion, several DiameterJ algorithms (M6, M5, T3) perform well for diameter determination from SEM images, given the appropriate imaging conditions (13–16 pixels/fiber). Determining fibrin clot porosity via DiameterJ is challenging.

Dysfibrinogenemia-Potential Impact of Genotype on Thrombosis or Bleeding

The congenital dysfibrinogenemias, most often associated with bleeding disorders, encompass mutations in the amino-terminal end of fibrinogen α-chain consisting of Gly17-Pro18-Arg19-Val20, known as knob A, which is a critical site for fibrin polymerization. Here we review the studies reporting dysfibrinogenemia due to mutations affecting fibrinogen knob A and identified 29 papers. The number of reports on dysfibrinogenemias related to residues Gly17, Pro18, Arg19, and Val20 is 5, 4, 18, and 2, respectively. Dysfibrinogenemias related to residues Gly17, Pro18, and Val20 are exclusively associated with bleeding tendency. However, the clinical picture associated with dysfibrinogenemia related to residue Arg19 varies, with most patients suffering from bleeding tendencies, but also transitory ischemic attacks and retinal thrombosis may occur. The reason for this variation is unclear. To elaborate the genotype-phenotype associations further, we studied a Danish family with knob A-related dysfibrinogenemia caused by the Aα Arg19Gly (p.Arg19Gly) mutation using whole-exome sequencing and fibrin structure analysis. Our family is the first reported carrying the p.Arg19Gly mutation combined with one or more single nucleotide polymorphisms (SNP)s in FGA, FGB, and/or FGG and increased fibrin fiber thickness and fibrin mass-to-length ratio suffering from pulmonary emboli, suggesting that compound genotypes may contribute to the thrombogenic phenotype of these patients. Our review, accordingly, focuses on significance of SNPs, compound genotypes, and fibrin structure measures affecting the genotype-phenotype associations in fibrinogen knob A mutations.

Fibrin Clot Properties in Atherosclerotic Vascular Disease: From Pathophysiology to Clinical Outcomes

Fibrin is a major component of thrombi formed on the surface of atherosclerotic plaques. Fibrin accumulation as a consequence of local blood coagulation activation takes place inside atherosclerotic lesions and contributes to their growth. The imbalance between thrombin-mediated fibrin formation and fibrin degradation might enhance atherosclerosis in relation to inflammatory states reflected by increased fibrinogen concentrations, the key determinant of fibrin characteristics. There are large interindividual differences in fibrin clot structure and function measured in plasma-based assays and in purified fibrinogen-based systems. Several observational studies have demonstrated that subjects who tend to generate denser fibrin networks displaying impaired clot lysis are at an increased risk of developing advanced atherosclerosis and arterial thromboembolic events. Moreover, the majority of cardiovascular risk factors are also associated with unfavorably altered fibrin clot properties, with their improvement following effective therapy, in particular with aspirin, statins, and anticoagulant agents. The prothrombotic fibrin clot phenotype has been reported to have a predictive value in terms of myocardial infarction, ischemic stroke, and acute limb ischemia. This review article summarizes available data on the association of fibrin clot characteristics with atherosclerotic vascular disease and its potential practical implications.

Lifestyle Influences Changes in Fibrin Clot Properties Over a 10-Year Period on a Population Level

Case-control and observational studies have provided a plausible mechanistic link between clot structure and thrombosis. We aimed to identify lifestyle, demographic, biochemical, and genetic factors that influence changes in total fibrinogen concentration and clot properties over a 10-year period in 2,010 black South Africans. Clot properties were assessed with turbidimetry and included lag time, slope, maximum absorbance, and clot lysis time. Linear mixed models with restricted maximum likelihood were used to determine whether (1) outcome variables changed over the 10-year period; (2) demographic and lifestyle variables, biochemical variables, and fibrinogen single-nucleotide polymorphisms influenced the change in outcome variables over the 10-year period; and (3) there was an interaction between the exposures and time in predicting the outcomes. A procoagulant risk score was furthermore created, and multinomial logistic regression was used to determine the exposures that were associated with the different risk score categories. In this population setting, female gender, obesity, poor glycemic control, increased low-density lipoprotein cholesterol, and decreased high-density lipoprotein cholesterol contributed to the enhanced progression to prothrombotic clot properties with increasing age. Alcohol consumption on the other hand, offered a protective effect. The above evidence suggest that the appropriate lifestyle changes can improve fibrin clot properties on a population level, decreasing cardiovascular disease risk and thus alleviate the strain on the medical health care system.

Effects of antithrombotic drugs on the prothrombotic state in patients with atrial fibrillation: The west Birmingham atrial fibrillation project

BACKGROUND

Direct oral anticoagulants (DOACs) are known to prevent thrombosis but there is limited information about their activity on the clot formation and lysis cascade.

OBJECTIVES

This study assesses the role of apixaban, one of the four licenced DOACs, on clot dynamics in patients with atrial fibrillation (AF).

METHODS

We compared haemostatic and clot lysis characteristics between a group of patients with AF (n = 47) and a "disease control" group with ischaemic heart disease but in sinus rhythm (n = 39). Subsequently, we conducted clot structure studies in 3 groups of patients with AF on different antithrombotic drugs: warfarin (n = 60), apixaban (n = 60) or antiplatelets (n = 62) and in patients with AF naïve to oral anticoagulants before and after 3-months treatment with apixaban (n = 32). Haemostasis was investigated by a viscoelastic, whole blood technique (Thromboelastography/TEG), a "microplate-reader based", citrated plasma technique (microplate assay), immunoassays to determine plasma concentrations of plasminogen activator inhibitor-1 (PAI-1), tissue-Plasminogen Activator (t-PA), D-dimer and finally platelet derived and apoptotic microparticles.

RESULTS

Patients with AF have more potent thrombogenesis based on microplate assay indices [Rate of clot formation (p = 0.03, ƞ² = 0.06), Maximum optical density (p < 0.001, ƞ² = 0.05)] and delayed fibrinolysis [Rate of clot dissolution (p = 0.005, ƞ² = 0.17)] with increased levels of apoptotic microparticles (p = 0.02, ƞ² = 0.06) compared with the 'disease control' group. Apixaban was more effective in attenuating prothrombotic characteristics assessed by TEG {R (ε² = 0.21), K (ε² = 0.16) and angle [mean difference (MD), 95% Confidence Intervals (CI), vs warfarin 5, 0.96-8.6 and 8, 3.8-11.4 vs antiplatelets], (p < 0.001 for all indices)} compared with the other treatment groups. Patients on apixaban had lower D-dimer (p < 0.001, ε² = 0.17) and tPA (p = 0.03, MD 90, 95%CI 6-150 vs warfarin and MD 90, 95% CI 4-150 vs antiplatelets) levels. From the microplate assay analysis, warfarin and apixaban demonstrated comparable activity based on multiple indices, both superior to antiplatelets. However, warfarin was associated with reduced fibrin network robustness (Max. optical density p < 0.001, ε² = 0.1). Apixaban inhibited thrombosis, amplified fibrinolysis and decreased D-dimer (p = 0.001, r = 0.4) levels in the follow up study.

CONCLUSIONS

Patients with AF have impaired haemostasis and elevated levels of apoptotic microparticles. Apixaban appears to affect plasma prothrombotic characteristics in a distinctive manner compared with warfarin and to reduce biomarkers associated with adverse cardiovascular events.

Impact of epicatechin on fibrin clot structure

Fibrin clot structure and function are major determinants of thromboembolic diseases. The study aim was to determine the impact of epicatechin (a flavonoid with cardiovascular protective effects) on fibrin clot structure and permeability. Plasma samples from 12 healthy subjects were incubated with increasing concentrations of epicatechin. Turbidity of fibrin clot was analyzed by absorbance measurement at 405 nm. The fibrin clot nanostructure was determined by scanning spectrometry (wavelength from 500 to 800 nm) and fibrin fiber size by electron microscopy. Permeability was analyzed to assess the fibrin clot functional properties. Epicatechin addition increased the maximum absorbance from 0.34 ± 0.066 (vehicle) to 0.35 ± 0.077 (P = 0.1), 0.35 ± 0.072 (P < 0.05) and 0.34 ± 0.065 (P = 0.5) for 1, 10 and 100 μM epicatechin, respectively. Epicatechin increased the fibrin clot fiber radius (nm) from 109.2 ± 3.2 (vehicle) to 108.9 ± 4.3 (P = 0.9), 110.0 ± 3.6 (P < 0.05) and 109.5 ± 3.3 (P = 0.4), and the distance between protofibrils (nm) from 22.2 ± 1.5 (vehicle) to 22.1 ± 2.3 (P = 0.9), 22.6 ± 1.8 (P < 0.05) and 22.3 ± 1.8 (P = 0.9) for 1, 10 and 100 μM epicatechin respectively. Electron microscopy confirmed these changes. Fibrin clot permeability, expressed as Darcy's constant (Ks, cm²), increased from 2.97 ± 1.17 (vehicle) to 3.36 ± 1.21 (P < 0.05), 3.81 ± 1.41 (P < 0.01) and 3.38 ± 1.33 (P = 0.9). Upon epicatechin addition, the fibrin clot structure became less dense and more permeable.

Reductions in plasmin inhibitor and fibrinogen predict the improved fibrin clot lysis 6 months after obesity surgery

Prothrombotic and metabolic variables are decreased after obesity surgery, and fibrin clot lysis is increased. It is unknown how fibrinolytic variables are affected, and whether fibrinolytic and metabolic changes predict the enhanced clot lysis. Study aims were to determine fibrinolytic biomarkers before and 6 months after Roux-en-Y gastric bypass (RYGB) and to identify predictors of the RYGB-induced increase in clot lysis. Women (n = 42) and men (n = 18) with obesity underwent RYGB, and factor XIII (FXIII), thrombin activatable fibrinolysis inhibitor (TAFI), plasminogen and plasmin inhibitor (PI) were measured before and 6 months after surgery. Regression analyses identified determinants of the RYGB-induced increase in clot lysis among changes in fibrinogen and in fibrinolytic and metabolic variables. Results showed that after RYGB, FXIII, TAFI, plasminogen and PI were reduced (P < .0005). Reductions in PI (β = -0.59) and fibrinogen (β = -0.35), together with age (β = -0.22) and male sex (β = 0.22), predicted the enhanced clot lysis with the model explaining 56% (P < .0005). Predictors of the reduction in PI were reductions in cholesterol (β = 0.37) and glucose (β = 0.29), together with male sex (β = -0.28), whereas reductions in fibrinogen were predicted by lowering of interleukin-6 (IL-6) (β = 0.32). In conclusion, fibrinolytic variables were reduced 6 months after RYGB. Targeting PI and fibrinogen, by reducing metabolic variables such as glucose, cholesterol and IL-6, has a profibrinolytic effect in obesity.

Effects of Diabetes Mellitus on Fibrin Clot Structure and Mechanics in a Model of Acute Neutrophil Extracellular Traps (NETs) Formation

Subjects with diabetes mellitus (DM) have an increased risk of arterial thrombosis, to which changes in clot structure and mechanics may contribute. Another contributing factor might be an increased formation of neutrophil extracellular traps (NETs) in DM. NETs are mainly formed during the acute phase of disease and form a network within the fibrin matrix, thereby influencing clot properties. Previous research has shown separate effects of NETs and DM on clot properties, therefore our aim was to study how DM affects clot properties in a model resembling an acute phase of disease with NETs formation. Clots were prepared from citrated plasma from subjects with and without DM with the addition of NETs, induced in neutrophils by S. aureus bacteria or phorbol myristate acetate (PMA). Structural parameters were measured using scanning electron microscopy, mechanical properties using rheology, and sensitivity to lysis using a fluorescence-based fibrinolysis assay. Plasma clots from subjects with DM had significantly thicker fibers and fewer pores and branch points than clots from subjects without DM. In addition, fibrinolysis was significantly slower, while mechanical properties were similar between both groups. In conclusion, in a model of acute NETs formation, DM plasma shows prothrombotic effects on fibrin clots.

From Routine to Research Laboratory: Strategies for the Diagnosis of Congenital Fibrinogen Disorders

Congenital fibrinogen disorders (CFDs) encompass a heterogeneous group of fibrinogen defects with a wide spectrum of biological and clinical features. An accurate diagnosis is thus essential to assure the optimal management for the patient. Diagnosis involves a multistep approach starting with routine coagulation assays and assessment of functional and antigenic fibrinogen followed by identification of the molecular anomaly. However, the diagnosis of CFD can be challenging as the sensitivity and specificity of coagulation assays depend on the fibrinogen level as well as on the fibrinogen variant. In addition, patients suffering from CFD have a heterogeneous clinical course which is often unpredictable by routine coagulation assays. To better determine the patient's clinical phenotype, global hemostasis assays and an assessment of the fibrin clot properties are performed in research laboratories. In this review, we summarize the fibrinogen work-up highlighting some common pitfalls and provide an update of the research on CFD.

The ABO Locus is Associated with Increased Fibrin Network Formation in Patients with Stable Coronary Artery Disease

BACKGROUND

 The ABO locus has been associated with increased risk of myocardial infarction (MI) in patients with coronary artery disease (CAD), but the underlying mechanisms are unknown. As altered fibrin clot structure has been demonstrated to predict MI in CAD patients, we examined the association between the ABO risk variant and fibrin clot properties, and investigated the effects of other CAD-associated risk variants.

METHODS

 We included 773 stable CAD patients. Patients were genotyped for 45 genome-wide CAD risk variants, including rs495828 at the ABO locus. We used a genetic risk score (GRS) for CAD calculated as the weighted sum of the number of risk alleles based on all 45 variants. Fibrin clot properties were evaluated using a turbidimetric assay. We studied clot maximum absorbance, a measure of clot density and fiber thickness, together with clot lysis time, an indicator of fibrinolysis potential.

RESULTS

 The rs495828 risk allele was present in 13.2% of patients and associated with higher clot maximum absorbance (adjusted effect size per risk allele: 1.05 [1.01 - 1.09], p = 0.01) but not with clot lysis time (p = 0.97). The rs12936587 (p = 0.04), rs4773144 (p = 0.02), and rs501120 (p = 0.04) were associated with clot lysis time; however, after Bonferroni correction, no significant associations were found between any of the remaining 44 CAD-associated variants and fibrin clot properties. The GRS was not associated with fibrin clot properties (p-values > 0.05).

CONCLUSION

 The ABO risk allele was associated with a more compact fibrin network in stable CAD patients, which may represent a mechanism for increased MI risk in ABO risk variant carriers.