Global/integral assays in hemostasis diagnostics: promises, successes, problems and prospects

Integral assays of hemostasis in hospitalized patients with COVID-19 on admission and during heparin thromboprophylaxis

BACKGROUND

Blood coagulation abnormalities play a major role in COVID-19 pathophysiology. However, the specific details of hypercoagulation and anticoagulation treatment require investigation. The aim of this study was to investigate the status of the coagulation system by means of integral and local clotting assays in COVID-19 patients on admission to the hospital and in hospitalized COVID-19 patients receiving heparin thromboprophylaxis.

METHODS

Thrombodynamics (TD), thromboelastography (TEG), and standard clotting assays were performed in 153 COVID-19 patients observed in a hospital setting. All patients receiving treatment, except extracorporeal membrane oxygenation (ECMO) patients (n = 108), were administered therapeutic doses of low molecular weight heparin (LMWH) depending on body weight. The ECMO patients (n = 15) were administered unfractionated heparin (UFH).

RESULTS

On admission, the patients (n = 30) had extreme hypercoagulation by all integral assays: TD showed hypercoagulation in ~75% of patients, while TEG showed hypercoagulation in ~50% of patients. The patients receiving treatment showed a significant heparin response based on TD; 77% of measurements were in the hypocoagulation range, 15% were normal, and 8% remained in hypercoagulation. TEG showed less of a response to heparin: 24% of measurements were in the hypocoagulation range, 59% were normal and 17% remained in hypercoagulation. While hypocoagulation is likely due to heparin treatment, remaining in significant hypercoagulation may indicate insufficient anticoagulation for some patients, which is in agreement with our clinical findings. There were 3 study patients with registered thrombosis episodes, and all were outside the target range for TD parameters typical for effective thromboprophylaxis (1 patient was in weak hypocoagulation, atypical for the LMWH dose used, and 2 patients remained in the hypercoagulation range despite therapeutic LMWH doses).

CONCLUSION

Patients with COVID-19 have severe hypercoagulation, which persists in some patients receiving anticoagulation treatment, while significant hypocoagulation is observed in others. The data suggest critical issues of hemostasis balance in these patients and indicate the potential importance of integral assays in its control.

Evaluation of hemostasis disorders using the thrombodynamic test in patients with chronic glomerulonephritis with nephrotic syndrome

Background. Nephrotic syndrome (NS) is accompanied by a risk of thrombotic complications due to hypercoagulability. Routine laboratory tests are not sensitive enough to detect these disorders, and therefore the use of integral coagulation tests, including a new thrombodynamic test (TT) in patients with NS, is of high relevance. Aim. Using a TT to determine hemostasis disorders in patients with chronic glomerulonephritis (CGN) with NS. Materials and methods. The study included 49 patients with CGN, mean age 37 years, of which 25 (51%) women and 24 (49%) men. Of all the examined patients, 20 (40.8%) of people had NS, 29 (59.2%) had no NS. The process of clot formation was assessed by TT. Results. According to TT, 30% (6/20) of patients with NS and 13.7% (4/29) of patients without NS have hypercoagulation with changes in parameters that go beyond the reference values. In patients with NS, an increase in clot density (D), clot formation rate (V) and clot size (CS) was found, especially when albumin decreased below 25 g/l. Negative correlations were found between the levels of albumin, creatinine and clot density (D), which reflects the level of hyperfibrinogenemia, the rate of clot formation (V) and the integral index of coagulation (CS). The results indicate mainly the activation of the plasma hemostasis due to the internal coagulation pathway. However, the correlation of Tlag (delay time for the onset of clot formation after contact of blood plasma with the insert-activator) with serum cholesterol levels may also indicate activation of the extrinsic coagulation pathway. Conclusion. In CGN patients with NS, activation of the plasma hemostasis is noted, as evidenced by an increase in the rate of formation (V) and size of the clot (CS) after 30 minutes, as well as the density of the formed clot (D).

Thrombodynamics as a tool for monitoring hemostatic disorders in patients with chronic glomerulonephritis complicated by nephrotic syndrome

Nephrotic syndrome (NS) is associated with a high risk for venous and arterial thrombosis due to hypercoagulability. Integral tests designed to assess hemostasis can become an alternative for measuring hypercoagulability in patients with NS. STUDY OBJECTIVE: To assess hemostatic disorders in CGN patients complicated by NS using the thrombodynamics test. MATERIALS AND METHODS: The study included 60 adult patients with chronic glomerulonephritis (CGN), mean age 37 years, 31 (52%) women, and 29 (48%) men. Among all patients, 53 % of patients had NS, 47 % had no sign of NS. Hemostasis was assessed using the thrombodynamics test. The results were compared with biochemical parameters, which are usually associated with NS and renal dysfunction. RESULTS: According to the thrombodynamics test, CGN patients with NS demonstrated a tendency to hypercoagulability: increased rates of V (rate of clot growth), increased D (clot density), and increased CS (clot size) after 30 minutes. A positive correlation of these parameters with the serum albumin, creatinine levels, and glomerular filtration rate (GFR) indicates the influence of severe NS and renal dysfunction on the hemostasis activation in CGN patients with NS. CONCLUSION: According to the thrombodynamics test, CGN patients with NS demonstrate increased rates of clot formation, increased clot size after 30 minutes, and increased clot density due to secondary hemostasis activation. These changes positively correlate with the severity of hypoalbuminemia, hypercholesterolemia, and renal dysfunction in NS patients.

Added Value of Blood Cells in Thrombin Generation Testing

The capacity of blood to form thrombin is a critical determinant of coagulability. Plasma thrombin generation (TG), a test that probes the capacity of plasma to form thrombin, has improved our knowledge of the coagulation system and shows promising utility in coagulation management. Although plasma TG gives comprehensive insights into the function of pro- and anticoagulation drivers, it does not measure the role of blood cells in TG. In this literature review, we discuss currently available continuous TG tests that can reflect the involvement of blood cells in coagulation, in particular the fluorogenic assays that allow continuous measurement in platelet-rich plasma and whole blood. We also provide an overview about the influence of blood cells on blood coagulation, with emphasis on the direct influence of blood cells on TG. Platelets accelerate the initiation and velocity of TG by phosphatidylserine exposure, granule content release and surface receptor interaction with coagulation proteins. Erythrocytes are also major providers of phosphatidylserine, and erythrocyte membranes trigger contact activation. Furthermore, leukocytes and cancer cells may be important players in cell-mediated coagulation because, under certain conditions, they express tissue factor, release procoagulant components and can induce platelet activation. We argue that testing TG in the presence of blood cells may be useful to distinguish blood cell-related coagulation disorders. However, it should also be noted that these blood cell-dependent TG assays are not clinically validated. Further standardization and validation studies are needed to explore their clinical usefulness.

Comparative Analysis of Thrombin Calibration Algorithms and Correction for Thrombin-α2macroglobulin Activity

Background: The thrombin generation (TG) test is useful for characterizing global hemostasis potential, but fluorescence substrate artifacts, such as thrombin-α2macroglobulin (T-α2MG) signal, inner filter effect (IFE), substrate consumption, and calibration algorithms have been suggested as sources of intra- and inter-laboratory variance, which may limit its clinical utility. Methods: Effects of internal vs. external normalization, IFE and T-α2MG on TG curves in normal plasma supplemented with coagulation factors, thrombomodulin, and tissue factor were studied using the Calibrated Automated Thrombinography (CAT; Diagnostica Stago, Parsippany, NJ, USA) and in-house software. Results: The various calibration methods demonstrated no significant difference in producing TG curves, nor increased the robustness of the TG assay. Several TG parameters, including thrombin peak height (TPH), produced from internal linear calibration did not differ significantly from uncalibrated TG parameters. Further, TPH values from internal linear and nonlinear calibration with or without T-α2MG correction correlated well with TPH from external calibration. Higher coefficients of variation (CVs) for TPH values were observed in both platelet-free and platelet-rich plasma with added thrombomodulin. Conclusions: Our work suggests minimal differences between distinct computational approaches toward calibrating and correcting fluorescence signals into TG levels, with most samples returning similar or equivalent TPH results.

Kaolin, used to trigger coagulation in thrombin generation test, increases sensitivity of the method in hemophilia patients

: Thrombin generation test (TGT) is well established tool to research blood coagulation in plasma of hemophilia patients. Traditionally coagulation in this test is triggered by a tissue factor (TF), an extrinsic coagulation pathway activator. However, it is known that disorders of the intrinsic pathway are most important for coagulation in hemophilia. In this study, we hypothesized that triggering coagulation via the intrinsic pathway could increase a sensitivity of the TGT to monitor hemophilia treatment. The aim of this study was to compare thrombin generation in hemophilia A patients with inhibitors to factor VIII before and after infusion of bypassing agent [recombinant-activated factor VIIa (rVIIa)] using standard activation of coagulation by TF or by kaolin, an activator of coagulation by intrinsic pathway. Endogenous thrombin potential (ETP) in nine patients was measured. ETP before (ETP0) and 60 min after rVIIa infusion (ETP60) were compared. It was shown that ETP0 and ETP60 were significantly different when using any coagulation activator (paired Student's t test, P = 0.017 and 3.7 × 10 for clotting activation by TF and kaolin, respectively). The ratios of ETP60/ETP0 were 1.2 ± 0.2 or 30.0 ± 22.4 (mean ± SD, n = 9) for coagulation activated by TF or kaolin, respectively, and were significantly different (paired Student's t test, P < 0.005). The TGT clearly distinguished between ETP0 and ETP60 in the case of any coagulation activator, but ETP increasing after rVIIa infusion was significantly higher when activated with kaolin. This provided increased sensitivity of this method for monitoring hemophilia therapy.

Utilization of the Caprini score in conjunction with thrombodynamic testing reduces the number of unpredicted postoperative venous thromboembolism events in patients with colorectal cancer

BACKGROUND

The thrombodynamic test (TD) is a novel global test of hemostasis that allows to study the spatial-temporal characteristics of a clot formation in real time under conditions close to natural ones and demonstrates high sensitivity to detect the state of hypercoagulation. The main paraments of the test are the velocity of clot growth, clot's size, and clot density. The objective of this study was to compare the classic Caprini 2005 score and its modified version in association with the results of TD. The goal is to predict postoperative venous thromboembolism (VTE) in surgical patients undergoing surgery for colorectal cancer.

METHODS

This was a prospective observational clinical study involving 80 patients (33 men and 47 women; mean age, 73.9 ± 7.2 years) who underwent major (79 cases) or minor (1 case) surgery for colorectal cancer. Patients were at high risk for postoperative VTE (ie, a mean Caprini score of 9.9 ± 2.0) and received combined prophylaxis (ie, antiembolic compression stockings and enoxaparin 40 mg once daily) until discharge. Enoxaparin was administered at a fixed time of blood sampling for the TD test. Duplex ultrasound scan was performed to detect postoperative vein thrombosis before and 5 to 7 days after surgery.

RESULTS

Postoperative vein thrombosis was found in 21 of 80 patients (26.3%; 95% confidence interval, 17.9%-36.8%). Regression analysis and receiver operating characteristic (ROC) curve showed that Caprini scores significantly predicted VTE (P < .0001; area under the curve [AUC] = 0.839 ± 0.045). Analysis of ROC curve coordinates showed that a cutoff point of 11 scores had a sensitivity of 76.2% and a specificity of 74.6%. The results of the TD test showed significant hypercoagulation despite enoxaparin administration in patients with VTE. Regression analysis and ROC curves demonstrated that the following TD parameters had the greatest predictability for postoperative DVT: initial velocity of clot growth (Vin) and clot size (CS) measured at 12 hours after enoxaparin administration (AUC, 0.697 ± 0.063 and AUC, 0.790 ± 0.059, respectively), as well as Vin and CS measured 24 hours after the enoxaparin injection (S = 0.847 ± 0.059 and S = 0.803 ± 0.069, respectively). The cutoff points for VTE prediction at 12 and 24 hours seemed to be a Vin of greater than 62.5 and greater than 64.5 μm/minute (normal range, 35-56 μm/minute) as well as a CS of greater than 1351.5 and greater than 1333.5 μm (normal range, 800-1200 μm), respectively. Identified thresholds for TD parameters have been integrated into Caprini scores under the item "other congenital or acquired thrombophilia." The total Caprini scores were recalculated in patients where one or all TD parameters had exceeded the cutoff followed by reanalysis of the ROC curves. The best predictability was found for Caprini scores considering the elevation of all four TD parameters (AUC, 0.924 ± 0.029) with increased cutoff to a score of 12 with a sensitivity of 85.7% and a specificity of 81.4%. The use of cutoffs for the original and modified scores could be used to calculate the number of patients that were under cutoff but developed with VTE: 10.2% and 5.9%, respectively.

CONCLUSIONS

Integrating TD parameters into the Caprini score increases the ability to predict postoperative VTE.

Impaired platelet activity and hypercoagulation in healthy term and moderately preterm newborns during the early neonatal period

BACKGROUND

Preterm newborns are at thrombohemorrhagic risk during the early neonatal period. Taking into account the lack of informative tools for the laboratory diagnosis of hemostasis disorders in newborns, our goal was to determine the baseline values of thrombodynamics and platelet functional activity in healthy term and moderately preterm newborns during the early neonatal period future potential clinical use of these tests.

METHODS

Coagulation was assessed using an integral assay of thrombodynamics and standard coagulation assays, and platelet functional activity was estimated by flow cytometry.

RESULTS

Hypercoagulation of newborns, represented by a significantly higher clot growth velocity and the presence of spontaneous clots in the thrombodynamics, was combined with platelet hypoactivity. Granule release, phosphatidylserine exposure, and the ability to change shape upon activation were decreased in the platelets of moderately preterm newborns. The platelet function remained at the same level over the first four days of life, whereas the hypercoagulation became less pronounced.

CONCLUSIONS

The hemostasis of newborns is characterized by hypercoagulation combined with reduced platelet functional activity. Moderately preterm and term newborns do not differ in the parameters of coagulation, while some of the functional responses of platelets are lower in moderately preterm newborns than in term.

Shifting Landscape of Hemophilia Therapy: Implications for Current Clinical Laboratory Coagulation Assays

Clinical coagulation assays are an integral part of diagnosing and managing patients with hemophilia; however, in this new era of bioengineered factor products and non-factor therapeutics, problems have arisen with use of traditional coagulation tests for the quantification of several of these new products. Discussion over the use of one-stage clotting assays versus chromogenic substrate assays for clinical decision making and potency labeling has been ongoing for many years. Emerging factor concentrates have heightened concern over assay selection and availability. Emicizumab interferes with all aPTT based assays, rendering them unreliable and potentially falsely reassuring to the unaware provider. This review explores considerations for coagulation assays in the clinical setting and highlights how awareness of institutional coagulation assays and potential limitations have never been more critical for providers caring for patients with bleeding disorders. This article is protected by copyright. All rights reserved.

Thrombodynamics, a new global coagulation test: Measurement of heparin efficiency

The actual coagulation status may be reliably measured using only highly sensitive global functional tests; however, they are not numerous and all of them have disadvantages. Thrombodynamics (TD), a novel global coagulation test, is sensitive to hypo- and hypercoagulable states. The main properties of this test were investigated, and its capabilities for hemostasis analysis were verified through pharmacodynamic monitoring of the most widely used anticoagulants, heparins. The anticoagulant effects in the plasma of donors (n = 20) and patients after hip replacement (n = 20) spiked with unfractionated heparin or enoxaparin were measured in vitro to eliminate the influence of pharmacokinetic factors. Sensitivity for heparins was compared for activated partial thromboplastin time, thrombin generation tests and TD. TD was shown to reliably characterize the pharmacodynamics of any heparin in the entire range of its prophylactic and therapeutic concentrations. Inter-individual variability for the anticoagulant action of heparins was also calculated using the TD data. This variability did not differ between the investigated groups and did not exceed 12% and 20% for the stationary clot growth rate in the presence of unfractionated heparin and enoxaparin, respectively. That finding was in accordance with the values determined earlier using the thrombin generation test. The study results showed that TD has advantages over the other global methods of coagulation analysis. These advantages are good standardization, high reproducibility, independence of the parameter values from patient age and gender, and a narrower parameter distribution in a normal population. These results indicate that TD is a promising universal assessment method that improves the quality of hemostasis analysis because it more reliably detects deviations from the parameters' reference values.

Peripartum Haemorrhage: Haemostatic Aspects of the New German PPH Guideline

Summary Peripartum haemorrhage remains one of the main causes of maternal mortality world-wide. The German, Austrian and Swiss Societies of Gynaecology and Obstetrics have updated the current guidelines for the treatment of peripartum haemorrhage together with the German Society of Anaesthesiology and Intensive Care Medicine and the Society of Thrombosis and Haemostasis Research. The recommendations have been the result of a thorough review of the available scientific literature and a consensus process involving all members of the guideline group. A key element of the anaesthesiological and haemostatic management is the development of a multidisciplinary standard operating procedure combining surgical as well as medical and haemostatic treatments depending on the severity of bleeding. The guideline underscores the value of clinical and laboratory diagnostics of peripartum haemorrhage as early as possible, even pre-emptively. This allows for an early identification of causes of bleeding and a specific treatment. The guideline comprises evidence-based recommendations for the use of uterotonics, tranexamic acid and blood products such as factor concentrates, fresh frozen plasma, platelet concentrates, packed red blood cells, recombinant activated factor VII and desmopressin. In addition, recommendations for blood conservation strategies involving the use of cell salvage, permissive hypotension and transfusion triggers are given.

Random Forests Are Able to Identify Differences in Clotting Dynamics from Kinetic Models of Thrombin Generation

Current methods for distinguishing acute coronary syndromes such as heart attack from stable coronary artery disease, based on the kinetics of thrombin formation, have been limited to evaluating sensitivity of well-established chemical species (e.g., thrombin) using simple quantifiers of their concentration profiles (e.g., maximum level of thrombin concentration, area under the thrombin concentration versus time curve). In order to get an improved classifier, we use a 34-protein factor clotting cascade model and convert the simulation data into a high-dimensional representation (about 19000 features) using a piecewise cubic polynomial fit. Then, we systematically find plausible assays to effectively gauge changes in acute coronary syndrome/coronary artery disease populations by introducing a statistical learning technique called Random Forests. We find that differences associated with acute coronary syndromes emerge in combinations of a handful of features. For instance, concentrations of 3 chemical species, namely, active alpha-thrombin, tissue factor-factor VIIa-factor Xa ternary complex, and intrinsic tenase complex with factor X, at specific time windows, could be used to classify acute coronary syndromes to an accuracy of about 87.2%. Such a combination could be used to efficiently assay the coagulation system.

New Infestin-4 Mutants with Increased Selectivity against Factor XIIa

Factor XIIa (fXIIa) is a serine protease that triggers the coagulation contact pathway and plays a role in thrombosis. Because it interferes with coagulation testing, the need to inhibit fXIIa exists in many cases. Infestin-4 (Inf4) is a Kazal-type inhibitor of fXIIa. Its specificity for fXIIa can be enhanced by point mutations in the protease-binding loop. We attempted to adapt Inf4 for the selective repression of the contact pathway under various in vitro conditions, e.g., during blood collection and in ‘global’ assays of tissue factor (TF)-dependent coagulation. First, we designed a set of new Inf4 mutants that, in contrast to wt-Inf4, had stabilized canonical conformations during molecular dynamics simulation. Off-target activities against factor Xa (fXa), plasmin, and other coagulation proteases were either reduced or eliminated in these recombinant mutants, as demonstrated by chromogenic assays. Interactions with fXIIa and fXa were also analyzed using protein-protein docking. Next, Mutant B, one of the most potent mutants (its K_i for fXIIa is 0.7 nM) was tested in plasma. At concentrations 5–20 μM, this mutant delayed the contact-activated generation of thrombin, as well as clotting in thromboelastography and thrombodynamics assays. In these assays, Mutant B did not affect coagulation initiated by TF, thus demonstrating sufficient selectivity and its potential practical significance as a reagent for coagulation diagnostics.