Consensus instability equations for routine coagulation tests

OBJECTIVES

The stability of plasma samples for basic coagulation tests, prothrombin time (PT) and activated partial thromboplastin time (aPTT), has been widely studied. Recently, the Clinical and Laboratory Standards Institute (CLSI) updated its recommendations, extending the acceptable time frame for aPTT. These guidelines are based on experimental studies, which define limits according to different maximum permissible error (MPE) criteria. This study compiles raw data from 43 studies published over the last 30 years to develop a consensus instability equation that describes degradation independently of specific study parameters.

METHODS

A critical literature review was performed by collecting studies that included experimental stability data for PT, aPTT and the main procoagulant factors. The raw data of percentage deviation (PD%), time, and seven classification variables related to sample collection and handling were analysed. A regression model through the origin was applied to derive global instability equations and to assess influencing variables.

RESULTS

In frozen samples, PT and aPTT showed similar stability, with an average prolongation of 0.8 % per month. In non-frozen samples, tube handling affected stability more than storage temperature. The consensus equation for PT showed a linear average deterioration of 2.9 % per day, but model strength was limited. For aPTT, the consensus equation fitted better to a logarithmic decay model and predicted prolongations of 6.1 and 10 % at 6 and 24 h, respectively.

CONCLUSIONS

The consensus instability equations obtained in this review provide a robust model for assessing coagulation tests stability, aligning with expert recommendations. These equations improve the understanding of sample degradation and systematic error quantification.

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.

Evaluation of Citrated Plasma After Thawing for Routine Coagulation Testing

OBJECTIVE

We aim to find the time in which a thawed citrate plasma sample that was preserved can be analyzed for routine coagulation testing without losing precision.

METHODS

Whole blood samples from 30 healthy volunteers were collected in 3.2% sodium citrate vacutainer and centrifuged to separate platelet-poor plasma. Each sample was then aliquoted, one aliquot was used immediately for prothrombin time (PT)-international normalized ratio (INR) and activated partial thromboplastin time (APTT), four were stored at -20°C, and four were stored at -80°C for 24 hours. After 24 hours, the aliquots were taken out and thawed at 37°C in water bath and analyzed after 15, 30, 60, and 120 minutes.

STATISTICAL ANALYSIS

Data were presented as mean with standard deviation (SD). Repeated measures ANOVA with Tukey post-hoc test was performed for multiple comparisons. All analysis was done using GraphPAD Prism 8.0 software (GraphPad Software, San Diego, California, USA).  Results: In the case of PT and INR, no statistically significant difference was found between the mean values after thawing for 120 minutes when compared with the mean baseline value. However, the APTT showed a statistically significant difference (p = 0.0232) after 30 minutes of thawing when the sample was stored at -20°C. Furthermore, a statistically significance difference (p = 0.0001) was found after 60 minutes of thawing when the samples were stored at -80°C.

CONCLUSION

Plasma samples for the PT and INR may be accepted for assessment up to 120 minutes, when stored at -20°C and -80°C for 24 hours. In the case of APTT, the plasma sample can be used for assessment up to 30 minutes after thawing when stored at -20°C and up to 60 minutes when stored at -80°C.

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.

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.

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.

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.

Is it acceptable to use coagulation plasma samples stored at room temperature and 4°C for 24 hours for additional prothrombin time, activated partial thromboplastin time, fibrinogen, antithrombin, and D-dimer testing?

INTRODUCTION

Coagulation laboratories are faced on daily basis with requests for additional testing in already analyzed fresh plasma samples. This prompted us to examine whether plasma samples stored at room temperature (RT), and 4°C for 24 hours can be accepted for additional prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen (Fbg), antithrombin (AT), and D-dimer testing.

METHODS

We measured PT, aPTT, Fbg in 50 and AT in 30 plasma samples with normal and pathological values, within 4 hours of blood collection (baseline results) and after 24-hours storage at RT (primary tubes), and 4°C (aliquots). D-dimer stability was investigated in 20 samples stored in primary tubes at 4°C.

RESULTS

No statistically significant difference between baseline results and results in samples stored at RT and 4°C was observed for PT (P=.938), aPTT (P=.186), Fbg (P=.962), AT (P=.713), and D-dimers (P=.169). The highest median percentage changes were found for aPTT, being more pronounced for samples stored at 4°C (13.0%) than at RT (8.7%).

CONCLUSION

Plasma samples stored both at RT and 4°C for 24 hours are acceptable for additional PT, Fbg, and AT testing. Plasma samples stored 24 hours in primary tubes at 4°C are suitable for D-dimer testing.