Has the time arrived to replace the quick prothrombin time test for monitoring oral anticoagulant therapy?

Evolving Paradigm of Prothrombin Time Diagnostics with Its Growing Clinical Relevance towards Cardio-Compromised and COVID-19 Affected Population

Prothrombin time (PT) is a significant coagulation (hemostasis) biomarker used to diagnose several thromboembolic and hemorrhagic complications based on its direct correlation with the physiological blood clotting time. Among the entire set of PT dependents, candidates with cardiovascular ailments are the major set of the population requiring lifelong anticoagulation therapy and supervised PT administration. Additionally, the increasing incidence of COVID affected by complications in coagulation dynamics has been strikingly evident. Prolonged PT along with sepsis-induced coagulopathy (SIC score > 3) has been found to be very common in critical COVID or CAC-affected cases. Considering the growing significance of an efficient point-of-care PT assaying platform to counter the increasing fatalities associated with cardio-compromised and coagulation aberrations propping up from CAC cases, the following review discusses the evolution of lab-based PT to point of care (PoC) PT assays. Recent advances in the field of PoC PT devices utilizing optics, acoustics, and mechanical and electrochemical methods in microsensors to detect blood coagulation are further elaborated. Thus, the following review holistically aims to motivate the future PT assay designers/researchers by detailing the relevance of PT and associated protocols for cardio compromised and COVID affected along with the intricacies of previously engineered PoC PT diagnostics.

Standardization of Prothrombin Time/International Normalized Ratio (PT/INR)

The prothrombin time (PT) represents the most commonly used coagulation test in clinical laboratories. The PT is mathematically converted to the international normalized ratio (INR) for use in monitoring anticoagulant therapy with vitamin K antagonists such as warfarin in order to provide test results that are adjusted for thromboplastin and instrument used. The INR is created using two major PT 'correction factors', namely the mean normal PT (MNPT) and the international sensitivity index (ISI). Manufacturers of reagents and coagulometers have made some efforts to harmonizing INRs, for example, by tailoring reagents to specific coagulometers and provide associated ISI values. Thus, two types of ISIs may be generated, with one being a 'general' or 'generic' ISI and others being reagent/coagulometer-specific ISI values. Although these play a crucial role in improving INR results between laboratories, these laboratories reported INR values are known to still differ, even when laboratories use the same thromboplastin reagent and coagulometer. Moreover, ISI values for a specific thromboplastin can vary among different models of coagulometers from a manufacturer using the same method for clot identification. All these factors can be sources of error for INR reporting, which in turn can significantly affect patient management. In this narrative review, we provide some guidance to appropriate ISI verification/validation, which may help decrease the variability in cross laboratory reporting of INRs.

Thrombin: An Approach to Developing a Higher-Order Reference Material and Reference Measurement Procedure for Substance Identity, Amount, and Biological Activities

Thrombin, the proteolytic enzyme that catalyzes the transformation of soluble fibrinogen to the polymerized fibrin clot, participates in multiple reactions in blood coagulation in addition to the clotting reaction. Although reference materials have existed for many years, structural characterization and measurement of biological activity have never been sufficient to permit claims of clear metrological traceability for the thrombin preparations. Our current state-of-the-art methods for protein characterization and determination of the catalytic properties of thrombin now make it practical to develop and characterize a metrologically acceptable reference material and reference measurement procedure for thrombin. Specifically, α-thrombin, the biologically produced protease formed during prothrombin activation, is readily available and has been extensively characterized. Dependences of thrombin proteolytic and peptide hydrolytic activities on a variety of substrates, pH, specific ions, and temperature are established, although variability remains for the kinetic parameters that describe thrombin enzymatic action. The roles of specific areas on the surface of the thrombin molecule (exosites) in substrate recognition and catalytic efficiency are described and characterized. It is opportune to develop reference materials of high metrological order and technical feasibility. In this article, we review the properties of α-thrombin important for its preparation and suggest an approach suitable for producing a reference material and a reference measurement procedure that is sensitive to thrombin’s catalytic competency on a variety of substrates.

Biology of Coagulation and Coagulopathy in Neurologic Surgery

Hemostasis is a cell-based process that is regulated in a tissue-specific manner by the differential expression of procoagulant and anticoagulant factors on endothelial cells from different sites throughout the vasculature. The central nervous system, in particular, exhibits unique mechanisms of hemostatic regulation that favor increased activity of the tissue factor pathway. This results in an unusually high degree of protection against hemorrhage, at the potential expense of increased thrombotic risk. Unfortunately, standard laboratory assays, including the PT and aPTT, do not accurately reflect the complexity of hemostasis in vivo; therefore, they cannot predict the risk of bleeding or thrombosis.

Warfarin monitoring with viscoelastic haemostatic assays, thrombin generation, coagulation factors and correlations to Owren and Quick prothrombin time

The anticoagulant warfarin is commonly monitored with prothrombin time (PT). Viscoelastic haemostatic assays (VHA) are primarily used in situations of acute bleeding to guide haemostatic therapy. Much research has focused on VHA monitoring of new oral anticoagulants. However, many patients are still anticoagulated with warfarin and effect of warfarin anticoagulation on VHA is uncertain. The aim of this study was to assess warfarin anticoagulation on three different VHA and compare these findings with prothrombin time (PT), coagulation factor analyses and a thrombin generation assay (TGA). Citrated whole blood was drawn from 80 patients admitted for routine PT-INR Owren. VHA analysis with ROTEM (EXTEM, INTEM and FIBTEM), ReoRox (Fibscreen 1 and 2) and Sonoclot (gbACT+) was performed. Blood was also drawn for plasma analysis with PT (PT-INR Owren and PT Quick), TGA and analysis of factors I, II, VII, IX and X. Extrinsically activated VHA, including ROTEM EXTEM and FIBTEM Clotting Time (CT) and ReoRox Fibscreen1 and 2 clot onset time 1 correlated moderately with PT-INR Owren , with R 0.66-0.71. These four variables were likely to be prolonged above reference interval in patients with prolonged PT-INR Owren >1.2. Two patients with normal ROTEM CTs had Owren PT-INRs >1.5. Warfarin affects extrinsically activated VHA variables of initial clotting. The role of VHA for clinical decision-making in patients planned for invasive procedures, such as spinal/epidural anaesthesia needs further study. None of the recent guidelines on regional anaesthesia include VHA testing to define adequate haemostasis.

Coagulation measurement from whole blood using vibrating optical fiber in a disposable cartridge

In clinics, blood coagulation time measurements are performed using mechanical measurements with blood plasma. Such measurements are challenging to do in a lab-on-a-chip (LoC) system using a small volume of whole blood. Existing LoC systems use indirect measurement principles employing optical or electrochemical methods. We developed an LoC system using mechanical measurements with a small volume of whole blood without requiring sample preparation. The measurement is performed in a microfluidic channel where two fibers are placed inline with a small gap in between. The first fiber operates near its mechanical resonance using remote magnetic actuation and immersed in the sample. The second fiber is a pick-up fiber acting as an optical sensor. The microfluidic channel is engineered innovatively such that the blood does not block the gap between the vibrating fiber and the pick-up fiber, resulting in high signal-to-noise ratio optical output. The control plasma test results matched well with the plasma manufacturer's datasheet. Activated-partial-thromboplastin-time tests were successfully performed also with human whole blood samples, and the method is proven to be effective. Simplicity of the cartridge design and cost of readily available materials enable a low-cost point-of-care device for blood coagulation measurements.

Monitoring of antivitamin K-dependent anticoagulation in rodents - Towards an evolution of the methodology to detect resistance in rodents

Vitamin K antagonists are used as rodenticides for pest control management. In rodents, prothrombin time is used to monitor their effect despite its limits and the emergence of many coagulation methods. The aim of this study is to explore different coagulation monitoring methods in order to propose the best method and the best parameter to monitor vitamin K antagonists effect in rodents. The coagulation function was thus monitored with global coagulation assays and specialty assays after difethialone administration in rats. Despite many parameters obtained by thromboelastometry, only clotting time and clot formation time obtained by ExTEM were modified. Their evolution was fast with doubling time respectively of 4.0h and 3.7h but their increases were delayed with a lag time higher than 8h. Conversely, prothrombin time evolution presented a lag time of only 2h, but a higher doubling time of 7.2h. The measurements of factor VII and X activities were the most sensitive assays to monitor vitamin K antagonists effect with almost no lag time and the fastest evolution. Nevertheless, factor X was shown to be the only key factor driving prothrombin time. Monitoring factor X activity enables to follow most effectively the anticoagulation status in rats after rodenticides administration.

Clinical presentation and blood gas analysis of multiple trauma patients for prediction of standard coagulation parameters at emergency department arrival

OBJECTIVES

Trauma-induced coagulopathy (TIC) in multiple trauma patients is a potentially lethal complication. Whether quickly available laboratory parameters using point-of-care (POC) blood gas analysis (BGA) may serve as surrogate parameters for standard coagulation parameters is unknown. The present study evaluated TraumaRegister DGU® of the German Trauma Society for correlations between POC BGA parameters and standard coagulation parameters.

METHODS

In the setting of 197 trauma centres (172 in Germany), 86,442 patients were analysed between 2005 and 2012. Of these, 40,129 (72% men) with a mean age 46 ± 21 years underwent further analysis presenting with direct admission from the scene of the accident to a trauma centre, injury severity score (ISS) ≥ 9, complete data available for the calculation of revised injury severity classification prognosis, and blood samples with valid haemoglobin (Hb) measurements taken immediately after emergency department (ED) admission. Correlations between standard coagulation parameters and POC BGA parameters (Hb, base excess [BE], lactate) were tested using Pearson's test with a two-tailed significance level of p < 0.05. A subgroup analysis including patients with ISS > 16, ISS > 25, ISS > 16 and shock at ED admission, and patients with massive transfusion was likewise carried out.

RESULTS

Correlations were found between Hb and prothrombin time (r = 0.497; p < 0.01), Hb and activated partial thromboplastin time (aPTT; r = -0.414; p < 0.01), and Hb and platelet count (PLT; r = 0.301; p < 0.01). Patients presenting with ISS ≥ 16 and shock (systolic blood pressure < 90 mmHg) at ED admission (n = 4,329) revealed the strongest correlations between Hb and prothrombin time (r = 0.570; p < 0.01), Hb and aPTT (r = -0.457; p < 0.01), and Hb and PLT (r = 0.412; p < 0.01). Significant correlations were also found between BE and prothrombin time (r = -0.365; p < 0.01), and BE and aPTT (r = 0.327, p < 0.01). No correlations were found between Hb, BE and lactate lactate.

CONCLUSIONS

POC BGA parameters Hb and BE of multiple trauma patients correlated with standard coagulation parameters in a large database analysis. These correlations were particularly strong in multiple trauma patients presenting with ISS > 16 and shock at ED admission. This may be relevant for hospitals with delayed availability of coagulation studies and those without viscoelastic POC devices. Future studies may determine whether clinical presentation/BGA-oriented coagulation therapy is an appropriate tool for improving outcomes after major trauma.

Global assays and the management of oral anticoagulation

Coagulation tests range from global or overall tests to assays specific to individual clotting factors and their inhibitors. Whether a particular test is influenced by an oral anticoagulant depends on the principle of the test and the type of oral anticoagulant. Knowledge on coagulation tests applicable in monitoring status and reversal of oral anticoagulation is a prerequisite when studying potential reversal agents or when managing anticoagulation in a clinical setting. Specialty tests based on the measurement of residual activated factor X (Xa) or thrombin activity, e.g., are highly effective for determining the concentration of the new generation direct factor Xa- and thrombin inhibitors, but these tests are unsuitable for the assessment of anticoagulation reversal by non-specific prohemostatic agents like prothrombin complex concentrate (PCC) and recombinant factor VIIa (FVIIa). Global coagulation assays, in this respect, seem more appropriate. This review evaluates the current status on the applicability of the global coagulation assays PT, APTT, thrombin generation and thromboelastography in the management of oral anticoagulation by vitamin K antagonists and the direct factor Xa and thrombin inhibitors. Although all global tests are influenced by both types of anticoagulants, not all tests are useful for monitoring anticoagulation and reversal thereof. Many (pre)analytical conditions are of influence on the assay readout, including the oral anticoagulant itself, the concentration of assay reagents and the presence of other elements like platelets and blood cells. Assay standardization, therefore, remains an issue of importance.

Prognostic impact of standard laboratory values on outcome in patients with sudden sensorineural hearing loss

Background

Aim of the present study was to evaluate prognostic factors, in particular standard laboratory parameters, for better outcome after idiopathic sudden sensorineural hearing loss (SSNHL).

Methods

Using a retrospective review, 173 patients were included presenting between 2006 and 2009 with unilateral SSNHL, ≥30 dB bone conduction in three succeeding frequencies between 0.125 to 8 kHz in pure tone audiometry (PTA), and a time interval between first symptoms and diagnostics ≤ 4 weeks. Hearing gain of <10 dB versus ≥10 dB in the affected ear in 6PTA values was the primary outcome criterion. Univariate and multivariate statistical tests were used to analyze predictors for better outcome.

Results

The initial hearing loss was 50.6 ± 27.2 dB. The absolute hearing gain was 15.6 ± 20.1 dB. Eighty-one patients (47%) had a final hearing gain of ≥10 dB. Low-frequency hearing loss (p <0.0001); start of inpatient treatment <4 days after onset (p = 0.018); first SSNHL (versus recurrent SSNHL, p = 0.001); initial hearing loss ≥ 60 dB (p < 0.0001); an initial quick value lower than the reference values (p = 0.040); and a pretherapeutic hyperfibrinogenemia (p = 0.007) were significantly correlated to better outcome (≥10 dB absolute hearing gain). Multivariate analysis revealed that first SSNHL (p = 0.004), start of treatment <4 days after onset (p = 0.015), initial hearing loss ≥ 60 dB (p = 0.001), and hyperfibrinogenemia (p = 0.032) were independent prognostic factors for better hearing recovery.

Conclusion

Better hearing gain in patients with hyperfibrinogenemia might be explained by the rheological properties of the applied therapy and supports the hypothesis that SSNHL is caused in part by vascular factors.

Evaluation of the Steelex M600H coagulometer prothrombin time-international normalized ratio assay with Steelex test reagents

INTRODUCTION

The aim of the present study was to validate prothrombin time (PT) international normalized ratio (INR) results obtained using Steelex test reagents and a Steelex coagulometer (Steelex Scientific Instrument Company, Beijing, China), in comparison with use of a well-established standard test employing Pacific Hemostasis reagents (Fisher Diagnostics, Middletown, VA, USA) and Teco Coatron A4 coagulometer (Teco Medical Instruments GmbH, Neufahrn, Germany).

MATERIALS AND METHODS

Between- and within-day coefficients of variation (CVs) of both assays were calculated using control samples provided by the test manufacturers. Samples from 90 subjects were collected and INR values were determined in a double-blind parallel manner employing both systems.

RESULTS

The within-day coefficients of variation (CVs) in INR estimates ranged from 2.6% (INR = 1.12) to 3.1% (INR = 2.51) for the Steelex system and from 2.1% (INR = 1.09) to 1.8% (INR = 2.8) for the Pacific test; the between-day values ran from 3.4% (INR = 1.16) to 7.9% (INR = 2.64) and from 3.3% (INR = 1.1) to 2.3% (INR = 2.7), respectively. Passing-Bablok fit of the of the Steelex and Pacific methods yielded the equation: Steelex INR = 0.85 (0.79-0.91) x Pacific INR + 0.12 (-0.02-0.21), whereas the CUSUM linearity P value was < 0.01. The mean bias as determined by the Bland-Altman test was -0.156 (-0.912-0.600).

CONCLUSION

The results obtained using Steelex reagents and the M600H coagulometer are not equivalent to those obtained using Pacific Hemostasis reagents and a Teco Coatron A4 coagulometer, at least in the therapeutic range.

Coagulation dynamics of a blood sample by multiple scattering analysis

We report a new technique to measure coagulation dynamics on whole-blood samples. The method relies on the analysis of the speckle figure resulting from a whole-blood sample mixed with coagulation reagent and introduced in a thin chamber illuminated with a coherent light. A dynamic study of the speckle reveals a typical behavior due to coagulation. We compare our measured coagulation times to a reference method obtained in a medical laboratory.

A New Generation Prothrombin Time Method for INR

Prothrombin time (PT) is the leading test for monitoring oral anticoagulation therapy (OAT). We sought to determine INR taking into account only active coagulation factors FII, FVII and FX without inhibition in patient plasmas and calibrator kits.We measured PT using a combined thromboplastin reagent. The calculation was based on a new PT method, which measures active coagulation factors (F II, F VII, FX) and corrects the errors caused by inactive coagulation factors.On this basis, an INR result with and without inhibition for individual patient samples was also calculated and applied to 200 plasma samples obtained from OAT patients. Conspicuous variation in inhibition between the four calibration kits was noted. The kinetics of this inhibition was closest to a noncompetitive pattern.The need of correction for INRs of single patients increases with higher INRs. At the same level of patient INRs the coagulation inhibiton varies markedly.It has been known that different thromboplastin reagents possess variable sensitivities, but this may depend on sensitivity in inactive coagulation factors. PT methods today measure the sum of active coagulation factors and inhibition of inactive coagulation factors. ISI calibrators contain variable amounts of inactive coagulation factors, which renders harmonisation of INR results.Application of the Acf-PT (INR(Acf)) presented in this work develops the PT methodology to measure the true coagulation activity in vivo for patient warfarin therapy without inhibition. INR(Inh) can evidently also be used for the diagnostics and follow-up of certain liver diseases.