Stability of Hemostasis Parameters in Whole Blood, Plasma, and Frozen Plasma: Literature Review and Recommendations of the SFTH (French Society of Thrombosis and Haemostasis)

Preanalytical sample management is critical for a proper assessment of hemostasis parameters, and may differ depending on prescribed tests or additional tests considered to be necessary after initial results. Although there is quite vast literature on this issue, the Working Group of the French Society of Thrombosis and Haemostasis (SFTH) deemed it necessary to make an in-depth literature review and propose recommendations for the proper handling of samples prior to hemostasis assays. This extensive assessment is accessible on-line in French at the SFTH website. Here, a more synthetic view of these recommendations is proposed, supported by easy-to-use tables. The latter respectively deal with the stability of whole blood or fresh plasma, frozen samples, and proper handling of samples forwarded on dry ice. Procedures are classified as recommended, acceptable, not conformed and lacking data. This work involved the retrieval of 125 references, first screened by a working group of 6 experts, then reviewed by 20 other experts in the field. The highly detailed conditions summarized in these tables will hopefully help hemostasis laboratories to secure the conditions recommended for sample collection and transportation. Moreover, as some conditions clearly lacked recommendations, this review can open new fields of investigation for hemostasis preanalytics.

The Impact of Continuous Veno-Venous Hemodiafiltration on the Efficacy of Administration of Prophylactic Doses of Enoxaparin: A Prospective Observational Study

BACKGROUND

Critically ill patients frequently require continuous renal replacement therapy (CRRT). During CRRT, particles up to 10 kDa in size, such as enoxaparin, may be removed. The aim of this study was to determine if patients receiving prophylactic doses of enoxaparin and treated with continuous veno-venous hemodiafiltration (CVVHDF) reach prophylactic values of anti-Xa factor activity.

METHODS

In this observational trial, we compared two groups: 20 patients treated with CVVHDF and 20 patients not treated with CVVHDF. All of them received prophylactic doses of 40 mg of enoxaparin subcutaneously. Anti-Xa factor activity was determined on the third day of receiving a prophylactic dose of enoxaparin. The first blood sample was taken just before the administration of enoxaparin, and other samples were taken 3 h, 6 h, and 9 h after the administration of a prophylactic dose of enoxaparin.

RESULTS

At 3 and 6 h after administration of enoxaparin in both groups, we observed a significant increase in anti-Xa factor activity from baseline, with the peak after 3 h of administration. There were no significant differences in the numbers of patients who had anti-Xa factor activity within the prophylactic range between CVVHDF and control groups.

CONCLUSION

CVVHDF has only a mild effect on the enoxaparin prophylactic effect measured by anti-Xa factor activity. Thus, it seems there is no need to increase the dose of enoxaparin for patients requiring CVVHDF.

Monitoring heparin therapy: stability of two different anti-Xa assays using blood samples collected in citrate-containing and CTAD tubes

BACKGROUND

Anti-factor Xa assays and activated partial thromboplastin time (aPTT) are mainly employed to monitor patients treated with heparins. According to the Clinical and Laboratory Standards Institute and the French Working Group on Haemostasis and Thrombosis, anti-factor Xa activity and aPTT should be tested within 2 h of blood sampling for unfractionated heparin (UFH) monitoring. However, discrepancies exist depending on the used reagents and collecting tubes. The study aim was to determine the stability of aPTT and anti-factor Xa measurements using blood samples collected in citrate-containing or citrate-theophylline-adenosine-dipyridamole (CTAD) tubes and stored for up to 6 h.

METHODS

Patients receiving UFH or low molecular weight heparin (LMWH) were enrolled; aPTT and anti-factor Xa activity were tested using two different analyser/reagent pairs (Stago and reagent without dextran sulfate; Siemens and reagent with dextran sulfate) after 1, 4 and 6 h of sample storage as whole blood or as plasma.

RESULTS

For UFH monitoring, comparable anti-factor Xa activity and aPTT results were obtained with both analyser/reagent pairs when samples were stored as whole blood before plasma isolation. With samples stored as plasma, anti-factor Xa activity and aPTT were not affected up to 6 h after sampling when using the Stago/no-dextran sulfate reagent pair. With the Siemens/dextran sulfate-containing reagent, aPTT was significantly altered after 4 h of storage. For LMWH monitoring, anti-factor Xa activity remained stable (whole blood and plasma) for at least 6 h. Results were comparable with citrate-containing and CTAD tubes.

CONCLUSIONS

Anti-factor Xa activity in samples stored as whole blood or plasma was stable for up to 6 h, regardless of the reagent (with/without dextran sulfate)/collection tube. Conversely, aPTT was more variable because other plasma parameters can influence its measure and complicate the interpretation of its variations after 4 h.

Evaluation of a Pediatric Enoxaparin Dosing Protocol and the Impact on Clinical Outcomes

OBJECTIVES

Enoxaparin has been studied for prophylaxis and treatment of thromboembolism in the pediatric population. Dose-finding studies have suggested higher mean maintenance dose requirements in younger children; however, the current recommended dosing schema endorsed by the American College of Chest Physicians remains conservative, likely secondary to limited data on the safety and efficacy of escalated starting doses. Primary objectives of this study included the identification of patient characteristics and risk factors with associations to anti-factor Xa (anti-Xa) values. The secondary objective was to determine an association between the initial anti-Xa value and thrombus resolution. Safety outcomes related to bleeding were also assessed.

METHODS

This retrospective cohort study reviewed records of all pediatric patients ≤18 years of age who were initiated on therapeutic subcutaneous enoxaparin between October 1, 2008, and October 1, 2018, at Children's Hospitals and Clinics of Minnesota for an indication of incident thrombus (N = 283).

RESULTS

Successful resolution of thrombus was directly associated with attaining a therapeutic anti-Xa concentration upon first laboratory evaluation. Other characteristics with associations to initial anti-Xa values included age, body mass index, and certain diagnoses. The rate of composite bleeding was consistent across concentrations of anti-Xa (p = 0.4944).

CONCLUSIONS

Despite adherence to protocol, the current enoxaparin dosing nomogram is only successful at achieving a therapeutic anti-Xa concentration (0.5-1.0 unit/mL) 55.8% of the time. A more aggressive enoxaparin dosing nomogram is warranted, as delaying time to therapeutic anti-Xa values impacts clinical outcomes, specifically thrombus resolution. Further investigation into characteristics with association to anti-Xa concentrations is needed.

Assessment of the analytical performances and sample stability on ST Genesia system using the STG-DrugScreen application

BACKGROUND

Thrombin generation testing has been used to provide information on the coagulation phenotype of patients. The most used technique is the calibrated automated thrombogram (CAT) but it suffers from a lack of standardization, preventing its implementation in routine. The ST Genesia is a new analyzer designed to assess thrombin generation based on the same principle as the CAT. Unlike the CAT system, the ST Genesia is a benchtop, fully automated analyzer, able to perform the analyses individually and not by batch, with strict control of variables such as temperature and volumes, ensuring, theoretically, maximal reproducibility.

OBJECTIVES

This study aimed at assessing the performance of the STG-DrugScreen application on the ST Genesia analyzer. We also aimed at exploring stability of plasma samples after freezing and defining a reference normal range.

RESULTS

Results demonstrated the excellent interexperiment precision of the ST Genesia and confirmed that the use of a reference plasma helps reducing the inter-experiments variability. Stability revealed that plasma samples are stable for at least 11 months at -70°C or lower, except for those containing low molecular weight heparins which have to be tested within 6 months. Freezing had no effect on the majority of thrombin generation parameters except on time to peak.

CONCLUSIONS

Our results suggest an easy implementation of thrombin generation with the use of ST Genesia in the routine laboratory. This will facilitate the design of multicentric studies and enable the establishment of reliable and evidence-based thresholds, which may improve the management of patients treated with anticoagulants.

Pathology consultation on anticoagulation monitoring: factor X-related assays

OBJECTIVES

To review various anticoagulation therapies and related laboratory monitoring issues, with a focus on factor X-related chromogenic assays.

METHODS

A case-based approach is used to review pertinent published literatures and product inserts of anticoagulation drugs and to look back on clinical use of factor X-related chromogenic assays.

RESULTS

The number of anticoagulants available to clinicians has increased greatly in the past decade. Whether and how these anticoagulants should be monitored are areas of uncertainty for clinicians, which can lead to misuse of laboratory assays and suboptimal patient management. Factor X-related assays are of particular concern because of the similar and often confusing test names. Based on a common clinical case scenario and literature review regarding anticoagulant monitoring, an up-to-date discussion and review of the various factor X-related assays are provided, focusing on the differences in test designs and clinical utilities between the chromogenic anti-Xa and chromogenic factor X activity assays.

CONCLUSIONS

Anticoagulation therapy and related laboratory monitoring are rapidly evolving areas of clinical practices. A good knowledge of relevant laboratory assays and their clinical applications is necessary to help optimize patient care.

Factors influencing enoxaparin anti-Xa activity in surgical critically ill patients

STUDY OBJECTIVE

The objectives of the present study were to describe the incidence of low anti-Xa levels defined as below 0.1 IU/mL in a general surgical intensive care unit population and to evaluate factors independently influencing anti-Xa activity.

DESIGN

A prospective study was undertaken.

SETTING

Thirty-six patients admitted to a general intensive care unit and receiving subcutaneous (SC) enoxaparin 30 mg twice daily for thromboprophylaxis between November 2003 and August 2005 were included in the study.

MEASUREMENTS AND MAIN RESULTS

After reaching steady state, anti-Xa activity was determined by chromogenic assay at 0, 3, 6, and 9 hours after injection. Anti-Xa levels below 0.1 IU/mL at any time were considered subtherapeutic. Areas under the curve (AUCs) for a 12-hour dosing interval were estimated. Factors influencing anti-Xa AUC were evaluated using linear regression. Two patients (5.6%) did not attain therapeutic levels defined as anti-Xa more than 0.1 IU/mL at 3 hours post dose. Median AUC was 1.84 IU·h/mL (interquartile range, 1.47 IU·h/mL). In the linear regression analysis, sex and creatinine clearance were significant predictors of anti-Xa AUC(0-12h) levels.

CONCLUSION

In the study, prophylactic SC enoxaparin in critically ill patients at the current 30 mg SC twice daily dosage attained an anti-Xa level more than 0.1 U/mL in nearly all patients. In addition, low creatinine clearances and female sex are associated with higher anti-Xa activity AUC(0-12h).