Determining the effect of freezing on coagulation testing: comparison of results between fresh and once frozen-thawed plasma

Positive antiphospholipid antibodies increase the risk of ischemic stroke in patients with atrial fibrillation

BACKGROUND

Antiphospholipid antibodies (aPL), including lupus anticoagulant, antibodies against β2 glycoprotein I (anti-β2GPI), and anticardiolipin (aCL) antibodies are associated with ischemic stroke (IS). Their prevalence and clinical relevance in atrial fibrillation (AF) remain unclear.

OBJECTIVES

To assess whether aPL are associated with increased risk of IS in AF patients despite anticoagulation.

METHODS

We conducted a post hoc analysis of aPL using blood samples from 243 consecutive AF patients enrolled in a cohort study. Markers of a prothrombotic state, including endogenous thrombin potential, fibrin clot permeability, and lysis time, were measured at baseline. During a median follow-up of 52 months, IS/transient ischemic attack and major bleeding were recorded.

RESULTS

We observed aPL at a moderate or high titer in 51 (21%) patients, including 17 (7%) with anti-β2GPI, 19 (7.8%) with aCL antibodies, and 37 (15.2%) with lupus anticoagulant. aPL-positive patients were more likely to have prior stroke (P = .01) and be active smokers (P = .03), along with increased endogenous thrombin potential (P = .02), without any changes in fibrin clot properties. Anti-β2GPI (hazard ratio, 4.38; 95% CI, 1.58-12.19) and aCL (hazard ratio, 4.70; 95% CI, 1.80-12.30) at a moderate or high titer were associated with IS during follow-up (n = 20; 1.9% per year). There were 23 major bleedings (2.1% per year) and 20 deaths (1.9% per year), which were not associated with aPLs.

CONCLUSION

Our study showed a relatively high prevalence of aPL positivity in AF patients, which was linked to an increased risk of IS/transient ischemic attack. This suggests that screening for aPL might help optimize anticoagulant therapy in such patients.

Evaluation of coagulation profile in dogs with ACTH-dependent hyperadrenocorticism compared to healthy dogs by rotational thromboelastometry (ROTEM)

Despite their low morbidity, thromboembolic events in hyperadrenocorticism are associated with high mortality. Identifying the main hemostatic abnormalities will improve the prophylactic approach of these canine patients. The aim of this study was to evaluate hemostatic alterations related with ACTH-dependent HAC and its association with hypercoagulable state. For this purpose, 25 dogs diagnosed with ACTH-dependent HAC were compared with 28 healthy dogs as a control group. The hemostatic variables included platelet count, antithrombin, fibrinogen, D-dimer, PT, aPTT, rotational thromboelastometry (ROTEM) and platelet aggregation. Results showed a hypercoagulable state in 32% (8/25) dogs by ROTEM, which had at least 2 of the next features: decreased coagulation time (CT) or clot formation time (CFT) on INTEM (5/25) or EXTEM (4/25); increased maximum clot firmness (MCF) on INTEM (9/25), EXTEM (6/25) and FIBTEM (9/25). These same variables had a significant difference (P≤ 0.05) compared with the control group, as well as the parameters of α-angle and CT. Median fibrinogen levels (310 vs.178 mg/dL), mean platelet aggregation (11.1 vs. 7.9 Ohms), median platelet count (360 vs. 225 ×103/µL) and mean antithrombin activity (140 vs. 119%) were increased in ACTH-dependent HAC dogs compared to control group. PT (7.1 vs. 8.0 seconds) and aPTT (11.6 vs. 15.2 seconds) were also shortened in ACTH-dependent HAC dogs. Our findings confirm the presence of a hypercoagulable tendency in dogs with HAC. Although multifactorial, fibrinogen concentration and MCF FIBTEM showed the relevance of this protein for hypercoagulability in HAC.

Commercial human frozen plasmas for local, cross-site and long-term comparability of coagulation analysers

Laboratory compliance implies to correlate instruments for coagulation parameter with a wide range of measure using patient samples or commercialized sets of frozen plasmas. The aim of this study was to evaluate the intra, inter-reproducibility and long-term stability of ExpertCor Routine (ECR) plasma sets (Stago) on different parameters. The study was realized in two laboratories on four different instruments. Inter-site and intra-site correlation of ECR sets for PT, aPTT, Fibrinogen, INR, factor V (FV) UFH and LMWH anti-Xa and intra-reproducibility of DDimer (DDI), factor VIII (FVIII:C) and antithrombin (AT) assays were tested. To evaluate ECR long-term stability, samples were tested until 180 after delivery in one laboratory. Intra-site evaluation correlation coefficients is around 1. All predefined criteria to fulfil good comparability between inter-site instruments are met with Passing slopes between 0.9 and 1.1 and intercepts ranging from -0.62 to 2.83%. Long-term stability evaluation does not show any deviation over 180 days for aPTT, fibrinogen, DDI, UFH, LMWH but a drift for FV with STA-NeoPTimal reagent. On contrary, AT and FVIII:C are not stable. PT in second has an excellent stability unlike PT in percentage. Our study validates the use of ECR sets for correlation between instruments and inter-sites agreement, as for parameters claimed on the products than for factor V and FVIII:C. The evaluation of stability confirming the possible extension of use for 180 days after delivery except for FVIII:C and AT. These plasmas sets are an excellent alternative to local plasma patient use to perform instrument comparison.

Effects of frozen storage conditions and freezing rate on the stability of coagulation proteins in human plasma

OBJECTIVES

Degradation of coagulation proteins in frozen plasma may influence assay results. The aims of this study were to explore the changes in coagulation parameters in patient plasma and internal quality control (IQC) after different freezing and storage conditions during the short-term and long-term periods.

METHODS

Platelet poor plasma was prepared from citrated peripheral blood collected from a group of healthy donors. The plasma was pooled, frozen and stored in a variety of freezing and storage conditions. The changes were monitored using routine coagulation assays, as well as factor VIII (FVIII) and protein S (PS) assays.

RESULTS

Plasma stored in liquid nitrogen (LN 2 ) or in -80°C showed long-term stable values for routine tests for a period of over 12 months, and 6 months for FVIII. Interestingly, the activated partial thromboplastin time (aPTT) showed a temporary significant prolongation over the first two weeks. Plasma frozen and stored in -40°C is not viable for aPTT and FVIII testing, otherwise it can be used for other parameters for up to 4 months. PS showed a significant increase in all frozen samples. Freezing rate has a significant impact on plasma quality and the final storage temperature influences the long-term stability.

CONCLUSION

The optimal storage conditions are ultra-low temperatures (LN 2 or -80°C) and the highest freezing rate possible. However, frozen plasma is not viable for IQC of aPTT during a period of two weeks after freezing. This study is unique in its conception as a practical guide for the handling of frozen plasma samples in modern laboratory settings.

Preanalytical Variables in Hemostasis Testing

Hemostasis testing performed in clinical laboratories are critical for assessing hemorrhagic and thrombotic disorders. The assays performed can be used to provide the information required for diagnosis, risk assessment, efficacy of therapy, and therapeutic monitoring. As such, hemostasis tests should be performed to the highest level of quality, including the standardization, implementation, and monitoring of all phases of the testing, which include the preanalytical, analytical, and post-analytical phases. It is well established that the preanalytical phase is the most critical component of the testing process, being the hands-on activities, including patient preparation for blood collection, as well as the actual blood collection, including sample identification and the post-collection handling to include sample transportation, processing, and storage of samples when testing is not performed immediately. The purpose of this article is to provide an update to the previous edition of coagulation testing-related preanalytical variables (PAV) and, when properly addressed and performed, can reduce the most common causes of errors in the hemostasis laboratory.

D-dimer Testing in Pulmonary Embolism with a Focus on Potential Pitfalls: A Narrative Review

D-dimer is a multifaceted biomarker of concomitant activation of coagulation and fibrinolysis, which is routinely used for ruling out pulmonary embolism (PE) and/or deep vein thrombosis (DVT) combined with a clinical pretest probability assessment. The intended use of the tests depends largely on the assay used, and local guidance should be applied. D-dimer testing may suffer from diagnostic errors occurring throughout the pre-analytical, analytical, and post-analytical phases of the testing process. This review aims to provide an overview of D-dimer testing and its value in diagnosing PE and discusses the variables that may impact the quality of its laboratory assessment.

Testing for Lupus Anticoagulants

Lupus anticoagulant (LA) is one of the three criteria antiphospholipid antibodies (aPLs) employed in classification, and by default diagnosis, of antiphospholipid syndrome (APS). Detection of LA is not via calibrated assays but is based on functional behavior of the antibodies in a medley of coagulation assays. A prolonged clotting time in a screening test is followed by demonstration of phospholipid dependence and inhibitory properties in confirmatory and mixing tests, respectively, which are modifications of the parent screening test. Complications arise because no single screening test is sensitive to every LA, and no test is specific for LA, because they are prone to interference by other causes of elevated clotting times. Several screening tests are available but the pairing of dilute Russell's viper venom time (dRVVT) with LA-sensitive activated partial thromboplastin time (aPTT) is widely used and recommended because it is proven to have good detection rates. Nonetheless, judicious use of other assays can improve diagnostic performance, such as dilute prothrombin time to find LA unreactive with dRVVT and aPTT, and the recently validated Taipan snake venom time with ecarin time confirmatory test that are unaffected by vitamin K antagonist and direct factor Xa inhibitor anticoagulation. Expert body guidelines and their updates have improved harmonization of laboratory practices, although some issues continue to attract debate, such as the place of mixing tests in the medley hierarchy, and areas of data manipulation such as assay cut-offs and ratio generation. This article reviews current practices and challenges in the laboratory detection of LA.

Stability of coagulation parameters in plasma samples at room temperature after one freeze/thaw cycle

INTRODUCTION

Sample freezing is a part of routine laboratory tasks because some coagulation parameters are analysed in batches to optimize reagent consumption. The coagulation parameter stability in fresh and frozen samples has been described, but data are scarcer after thawing. This study objective was to determine the stability of the main coagulation parameters (from blood withdrawn on siliconized CTAD tubes and double-centrifuged) after one freeze/thaw cycle to generate procedures for appropriate handling, storage and testing.

METHODS

Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, D-dimers, clotting factors (F), protein C, protein S, antithrombin, lupus anticoagulant (LA)-sensitive aPTT and diluted-Russel's viper venom time (dRVVT) were assessed in 60 plasma samples (n=30, normal range and n=30, outside the normal range). Thirty samples from anticoagulated patients [unfractionated heparin (UFH), low-molecular weight heparin (LMWH), apixaban or rivaroxaban] were assessed using specific anticoagulant assays. Frozen samples were thawed, and assays were performed at 15 min, 2, 4 and 6 h after thawing. The coagulation parameter stability was assessed with the method of rejection limit.

RESULTS

After thawing, aPTT, PT, fibrinogen, D-dimers, FII, FV, FX, FIX, FXI, FXII, PC and UFH anti-Xa activity remained stable for at least 6 h, FVII for 5 h, PS, AT, dRVVT screen assay and LMWH anti-Xa activity for 4 h, and LA-sensitive aPTT and apixaban-specific anti-Xa activity for 3 h. FVIII, dRVVT confirm assay and rivaroxaban specific anti-Xa activity were stable for 2 h.

CONCLUSION

These results suggest that sample stability for some haemostasis assays is limited after thawing.

International Council for Standardization in Haematology (ICSH) recommendations for processing of blood samples for coagulation testing

This guidance document has been prepared on behalf of the International Council for Standardization in Haematology (ICSH). The aim of the document is to provide guidance and recommendations for the processing of citrated blood samples for coagulation tests in clinical laboratories in all regions of the world. The following areas are included in this document: Sample transport including use of pneumatic tubes systems; clots in citrated samples; centrifugation; primary tube storage and stability; interfering substances including haemolysis, icterus and lipaemia; secondary aliquots-transport, storage and processing; preanalytical variables for platelet function testing. The following areas are excluded from this document, but are included in an associated ICSH document addressing collection of samples for coagulation tests in clinical laboratories; ordering tests; sample collection tube and anticoagulant; preparation of the patient; sample collection device; venous stasis before sample collection; order of draw when different sample types are collected; sample labelling; blood-to-anticoagulant ratio (tube filling); influence of haematocrit. The recommendations are based on published data in peer-reviewed literature and expert opinion.

Review of coagulation preanalytical variables with update on the effect of direct oral anticoagulants

There are many preanalytical variables (PAV) that are known to affect coagulation testing. The more commonly acknowledged PAV addressed by the clinical laboratory tend to start with their influence on blood collection, but realistically coagulation PAV starts with the patient, where the laboratory has less influence or control. Patient selection and appropriate timing for blood collection may be integral for assuring proper diagnosis and management. Laboratory control and assurance for ideal phlebotomy practice would mitigate most PAVs related to blood collection to minimize suboptimal sample collection. Laboratory oversight of sample transportation, processing and storage will assure sample integrity until testing can be facilitated. The purpose of this document is to review common PAV that should be taken into consideration when ordering, performing and interpreting a coagulation test result, with additional attention to the effect of direct oral anticoagulants (DOACs).

Impact of specific preclinical variables on coagulation biomarkers in cancer-associated thrombosis

Coagulation biomarkers are being actively studied for their diagnostic and prognostic value in patients with venous thromboembolism and cancer, as well as in the study of pathogenic mechanisms between cancer and thrombosis. For the results of such studies to be accurate and reproducible, attention must be paid to minimize sources of error in all phases of testing. The pre-analytical phase of laboratory testing is known to be fraught with the majority of errors. Coagulation testing is particularly susceptible to conditions during collection, processing, transport and storage of specimens which can lead to clinically significant errors in results. In addition, changes in pre-analytical conditions can impact different biomarkers differently. Therefore, research studies investigating coagulation biomarkers must carefully standardize not just the analytical phase, but also the pre-analytical phase of testing to ensure accuracy and reliability. We briefly review the impact of pre-analytical conditions on coagulation testing in general, and on specific biomarkers in cancer and thrombosis. In addition, we provide recommendations to reduce pre-analytical errors by developing and sharing standard operating procedures that specifically target standardization of methodologies for collecting specimens and measuring current and emerging coagulation biomarkers in cancer studies.

International Council for Standardization in Haematology (ICSH) laboratory guidance for the verification of haemostasis analyser-reagent test systems. Part 2: Specialist tests and calibrated assays

Before a new method is used for clinical testing, it is essential that it is evaluated for suitability for its intended purpose. This document gives guidance for the performance, verification and implementation processes required by regulatory and accreditation bodies. It covers the planning and verification of specialist haemostatic tests, including factor assays, D-dimers, direct anticoagulants and thrombophilia testing.

Second trimester maternal serum D-dimer combined with alpha-fetoprotein and free β-subunit of human chorionic gonadotropin predict hypertensive disorders of pregnancy: a systematic review and retrospective case-control study

Background

This study investigated whether maternal serum D-dimer (DD) alone or DD combined with alpha-fetoprotein (AFP) and free β-subunit of human chorionic gonadotropin (free β-hCG) in the second trimester could be used to predict hypertensive disorders of pregnancy (HDP).

Materials and methods

In this retrospective case–control study, the data of gravidas patients who delivered at hospital were divided into the following groups: control (n = 136), gestational hypertension (GH, n = 126), preeclampsia (PE, n = 53), and severe preeclampsia (SPE, n = 41). Receiver operator characteristic (ROC) curves were used to evaluate the diagnostic value of maternal serum DD, AFP, and free β-hCG levels for HDP.

Results

DD levels of the GH, PE, and SPE groups were significantly higher than that of the control group (P < 0.001). The order of effectiveness for models predicting HDP was as follows: DD + AFP + free β-hCG > DD > DD + AFP > DD + free β-hCG > AFP + free β-hCG > AFP > free β-hCG. For predicting different types of HDP, DD alone had the best diagnostic value for SPE, followed by PE and GH. DD alone had a sensitivity of 100% with a 0% false negative rate and had the highest positive likelihood ratio (+ LR) for SPE. DD alone in combination with AFP alone, free β-hCG alone and AFP + free β-hCG could reduce false positive rate and improve + LR.

Conclusion

DD is possible the best individual predictive marker for predicting HDP. Levels of DD alone in the second trimester were positively correlated with the progression of elevated blood pressure in the third trimester, demonstrating the predicting the occurrence of HDP. The risk calculation model constructed with DD + free β-hCG + AFP had the greatest diagnostic value for SPE.

International Council for Standardization in Haematology (ICSH) laboratory guidance for the evaluation of haemostasis analyser-reagent test systems. Part 1: Instrument-specific issues and commonly used coagulation screening tests

Before a new method is used for clinical testing, it is essential that it is evaluated for suitability for its intended purpose. This document gives guidance for the performance of verification, validation and implementation processes required by regulatory and accreditation bodies. It covers the planning and execution of an evaluation of the commonly performed screening tests (prothrombin time, activated partial thromboplastin time, thrombin time and fibrinogen assay), and instrument-specific issues. Advice on selecting an appropriate haemostasis analyser, planning the evaluation, and assessing the reference, interval, precision, accuracy, and comparability of a haemostasis test system are also given. A second companion document will cover specialist haemostasis testing.

Comparison among different measurement systems for fibrinogen using fresh samples and frozen samples

BACKGROUND

Many laboratories in China have several types of coagulation analyzers. Differences in fibrinogen results among different systems may cause inappropriate medical decisions. Our aim was to set the comparability evaluation criteria and evaluate comparability of different fibrinogen measurement systems using fresh and frozen samples.

METHODS

Biological variation (BV) publications on fibrinogen were reviewed. Total error based on reliable BV data and external quality assessment (EQA) criteria were combined to set allowable limit. The compliance rate of samples for the limit should achieve at least 80% if the results obtained from different systems were comparable. Fifty-seven samples before and after freeze-thaw were measured by three measurement systems and the percentage of compliant samples was calculated.

RESULTS

The allowable limit was 11.3%. The compliance rates of fresh samples were 78.2-84.2%, and the rates of frozen samples were 54.5-93.0%. The comparability results were different using two kinds of samples.

CONCLUSIONS

It is feasible to set allowable limits of comparability based on BV and state of the art; and fresh samples are recommended for evaluating systems comparability. The results of comparability are related to samples' concentrations distribution, which should range over the concentration ranges in routine laboratory tests.

Impact of different preanalytical conditions on results of lupus anticoagulant tests

INTRODUCTION

The currently recommended preanalytical conditions for lupus anticoagulant (LA) analysis require analyzing samples in fresh or freshly frozen platelet-poor plasma. The aim of this study was to evaluate whether alternative and less cumbersome preanalytical procedures for LA testing give significantly different results compared to recommended conditions.

MATERIALS AND METHODS

Citrated blood samples were drawn from 29 study participants, 15 with negative and 14 with positive LA results. The samples were processed according to the ISTH guideline for LA testing and compared to several alternative preanalytical conditions. Measurements were performed using the dilute Russell's viper venom time (DRVVT) and silica clotting time (SCT), both screen and confirm, on a STA-R Evolution analyzer. Stability criteria were based upon biological variation.

RESULTS

All DRVVT tests (normalized screen, confirm, and screen/confirm ratio) met the stability criteria for all the preanalytical conditions. The SCT tests (normalized screen, confirm, and screen/confirm ratio) met the stability criteria only when treated according to the ISTH guideline, except for SCT normalized screen/confirm ratio which also met the stability criteria for double-centrifuged aliquoted plasma stored in room temperature for 24 hours and then analyzed "fresh" or after being frozen. One warfarin-treated patient was reclassified from positive to negative for DRVVT after the preanalytical modifications, while 2 of 29 participants became falsely positive for 2 of 8 conditions for SCT.

CONCLUSIONS

The DRVVT assays met the criteria for stability for all preanalytical conditions tested, while the SCT assays should be interpreted with caution if the preanalytical guidelines from ISTH are not followed.

D-dimer: Preanalytical, analytical, postanalytical variables, and clinical applications

D-dimer is a soluble fibrin degradation product deriving from the plasmin-mediated degradation of cross-linked fibrin. D-dimer can hence be considered a biomarker of activation of coagulation and fibrinolysis, and it is routinely used for ruling out venous thromboembolism (VTE). D-dimer is increasingly used to assess the risk of VTE recurrence and to help define the optimal duration of anticoagulation treatment in patients with VTE, for diagnosing disseminated intravascular coagulation, and for screening medical patients at increased risk of VTE. This review is aimed at (1) revising the definition of D-dimer; (2) discussing preanalytical variables affecting the measurement of D-dimer; (3) reviewing and comparing assay performance and some postanalytical variables (e.g. different units and age-adjusted cutoffs); and (4) discussing the use of D-dimer measurement across different clinical settings.

Resolving DOAC interference on aPTT, PT, and lupus anticoagulant testing by the use of activated carbon

BACKGROUND

Direct oral anticoagulants (DOACs) affect laboratory coagulations tests. Activated carbon (AC) can be used for adsorption of DOACs during acute human intoxications.

OBJECTIVES

This study evaluates whether AC can also be used to resolve DOAC interference on in vitro clotting tests (prothrombin time [PT], activated partial thromboplastin time [aPTT], and lupus anticoagulant [LA] assays).

PATIENTS/METHODS

Interference on PT, aPTT, Liquid anti-FXa, DTI, and LA screening/confirmation (SCT and dRVVT) was determined by spiking citrated plasma from 5 adult controls with 0, 20, 40, 80, 120, or 160 mg/mL AC. DOAC concentrations, PT, and aPTT were compared before and after AC addition to citrated plasma from patients receiving DOACs (n = 29), low molecular weight heparin (n = 10), and coumarin (n = 10) therapy. Samples from 69 LA screened patients were compared before and after AC addition.

RESULTS

A concentration of 20 mg/mL AC had the lowest interference and was selected for further experiments. After AC addition, all DOAC concentrations were below the limit of quantification in the 29 treated patients, except for 2 apixaban samples. AC removed DOAC interference on PT and aPTT but had no impact on results obtained during coumarin or low molecular weight heparin therapy. Of 15 LA samples with interference resulting from DOAC therapy, 14 samples became negative and 1 positive after AC addition. Interference from coumarin therapy was not resolved. All 19 LA negative samples remained negative. AC treatment of the negative pooled plasma was required to avoid false-negative LA results in 21 known LA-positive samples.

CONCLUSIONS

AC selectively removes DOAC interference on PT, aPTT, and LA assays.

Effect of Pre-analytical Conditions on Prothrombin Time and Partial Activated Thromboplastin Time

BACKGROUND

Clinical analysis often involves clotting assays. Although the guidelines suggest the storing and freezing of samples before these assays, there are contradictory results in the literature. The objective of this study was to analyse the effect of the temperature and the storage of plasma sample on Prothrombin Time (PT) and Activated Partial Thromboplastin Time (aPTT) in clinical samples for 65 patients without coagulation disorders.

MATERIALS AND METHODS

After centrifugation, plasma of each patient was tested at arrival as part of their routine care and separately aliquoted. Three aliquots were stored at room temperature, 4°C and - 20°C for 24h after collection, two aliquots were stored at 4°C and -20°C for 1 week and one aliquot was stored at -70°C for 1 month.

RESULTS

PT from healthy patients was affected at room temperature for 24h and at 4°C for 1 week. For aPTT, the results were statistically different for all the conditions after 24h and at 4°C for 1 week.

CONCLUSION

Results indicate that PT and aPTT can be stored at -70ºC for at least 1 month without any significant changes in the assay result.

Assessment of the Stability of von Willebrand Profile Clotting Factors and Platelet Dense Granule Testing Following Air Transport

The purpose of this study was to determine the reliability of test results dependent upon blood and plasma sample stability when shipped by airfreight courier for reference laboratory assessment. Of particular interest was evaluation of von Willebrand profile assays and platelet dense granule storage pool analysis. Peripheral venous blood was obtained from healthy volunteers. von Willebrand factor (VWF) activity, VWF antigen, and factor VIII coagulant activity assays were performed immediately following venipuncture with additional aliquots of plasma frozen and stored at −70°C for subsequent analysis 48 hours later. One frozen aliquot was shipped via airfreight for analysis 48 hours later, with another frozen aliquot that remained on-site. Blood was also collected to enumerate platelet dense granules to determine whether shipment would affect results. Statistical analysis of all test results demonstrated significant correlation between immediately assayed samples and samples that were stored for 48 hours at −70°C (P < .0001), or frozen and shipped on dry ice (P < .0001) for analysis upon return to our laboratory. No difference was found in the mean number of platelet dense granules between samples retained in our laboratory or samples analyzed upon return of shipment (P = .751).

Effects of preanalytical frozen storage time and temperature on screening coagulation tests and factors VIII and IX activity

Preanalytical quality control of blood samples is critical for tests of coagulation function and coagulation factor activity. Preanalytical storage time and temperature are the main variables. We investigated the effects of preanalytical frozen storage time and temperature on activated partial thromboplastin time (APTT), fibrinogen (Fbg), prothrombin time (PT)/international normalized ratio (INR), thrombin time (TT), factor VIII activity (FVIII:C), and factor IX activity (FIX:C) in frozen plasma. Samples (n = 144) were randomly and equally divided into four groups (storage at −80 °C or −20 °C) and analysed by CS5100 or CA7000 coagulation analysers. Baseline values and results after storage for 15 days, 1 month, 3 months, 6 months, and 1 year were measured after thawing. Mean percent changes and scatter plots were used to determine clinically relevant differences. The stabilities of coagulation tests and coagulation factor activities measured by the CS5100 system were consistent with those measured by the CA7000 system. At −80 °C, assessment samples of PT/INR, Fbg, and TT can be safely stored for 1 year, APTT for 6 months, and FVIII:C and FIX:C for 1 month. At −20 °C, samples of Fbg and TT can be stored for 1 year, PT/INR and FIX:C for 1 month, and APTT and FVIII:C for 15 days.

The effect of different methods of leucoreduction on plasma coagulation factors

Removal of leucocytes from blood products, namely leucoreduction, improves the safety of blood transfusion by reducing adverse events associated with the incidental transfusion of leucocytes. Coagulation factors might be compromised during leucoreduction because of exposure of plasma to a variety of filter materials. The aim of the current study was to assess the effect of different methods of prestorage leucofiltration (apheresis and whole blood filters) on prothrombin time, international normalized ratio, partial thromboplastin time and factors V and VIII. There was a significant prolongation of prothrombin time as well as elevation of international normalized ratio in plasma after leucoreduction (14.5 ± 0.7 s vs. 13.9 ± 0.7 s, P = 0.008 and 1.14 ± 0.07 vs. 1.09 ± 0.07, P = 0.005, respectively). Also, there was a statistically significant prolongation of activated partial thromboplastin time in nonleucoreduced plasma (55.6 ± 9.9 s vs. 43.2 ± 12.8 s, P = 0.001). There was no significant filtration effect on factors V and VIII levels. Furthermore, there was no significant difference in factors V and VIII levels between plasma filtered by inline whole blood filters and apheresis machine. Leucodepleted plasma originating from both inline whole blood filter and apheresis machine maintained satisfactory levels of factors V and VIII.

Laboratory monitoring of rivaroxaban and assessment of its bleeding risk

BACKGROUND

The aims of this study were to investigate the effects of rivaroxaban on routine coagulation assays using our local, widely available, reagents and to study the relationship between sensitive coagulation assays and bleeding risk caused by rivaroxaban.

METHODS

Prothrombin time (PT), activated partial thromboplastin time (APTT) and anti-factor Xa (FXa) chromogenic assays (Biophen DiXaI) and inhibition of FXa activity were performed in normal pooled plasma (NPP) spiked with rivaroxaban and plasma samples from patients treated with rivaroxaban.

RESULTS

In vitro, the linear correlation coefficient of measured concentrations of rivaroxaban, by Biophen DiXaI, and spiked concentrations of rivaroxaban was 0.99. PT and APTT showed good linear correlation with rivaroxaban concentrations, while other assays showed poor correlation. In vivo, PT showed a moderate linear correlation with rivaroxaban concentrations while APTT had a weak correlation with rivaroxaban concentrations. In vitro and in vivo, the rivaroxaban concentrations, measured by Biophen DiXaI, always showed good correlation with the inhibition of FXa activity, and PT values showed moderate correlation with the inhibition of FXa activity.

CONCLUSIONS

Biophen DiXaI can be considered as a quantitative method to monitor the anticoagulation activity of rivaroxaban, and could be used to evaluate bleeding risk caused by rivaroxaban. The PT reagent (Thrombosis S) could be considered as a rough method to monitor the anticoagulation activity of rivaroxaban and evaluate bleeding risk caused by rivaroxaban.

Evaluating the use of commercial drug-specific calibrators for determining PT and APTT reagent sensitivity to dabigatran and rivaroxaban

Suitable laboratory methodologies for quantifying the non-vitamin K oral anticoagulants (NOAC) include liquid chromatography-tandem mass spectrometry (LC-MS/MS) or drug-calibrated assays such as the dilute thrombin time for dabigatran or anti-Xa measurements for rivaroxaban. In situations when these tests are unavailable, it has been suggested that using commercial drug calibrators on APTT and PT assays would theoretically provide reagent sensitivity to these drugs. The purpose of this study was to determine whether commercial drug calibrators deliver similar reagent sensitivity information as samples from patients receiving dabigatran or rivaroxaban as part of their routine care. Two laboratory sites tested commercial calibrator material for dabigatran and rivaroxaban (Hyphen Biomedical) using PT and APTT reagents and data was compared to samples collected from patients taking NOACs that were quantified by LC-MS/MS. Correlation statistics and calculating the amount of drug required to double the clotting time of normal plasma were performed. All drug calibrator material correlated more strongly (R²> 0.95) for any reagent/drug combination than patient samples (R² ranged from 0.29-0.86). Dabigatran calibrator results and patient data were equivalent for SynthASil and PTT-A APTT reagents. The dabigatran and rivaroxaban calibrator material over-estimated drug sensitivity for all PT reagents when compared to sensitivity data calculated based on drug levels obtained by LC-MS/MS from patient samples. In conclusion, drug-specific calibrators overestimated reagent sensitivity which may underestimate in vivo drug concentration in a given patient. Further studies are required to assess whether this method of determining relative sensitivity of NOAC on routine coagulation assays should be recommended.