Influence of the centrifuge time of primary plasma tubes on routine coagulation testing

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.

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.

Interference of lipemia in samples for routine coagulation testing using a Sysmex CS-5100 coagulometer

INTRODUCTION

Lipemia in samples can cause analytical errors in coagulation tests using photometric assays. To define the level of this interference, some studies assessed lipemic interferences by in vitro 'spiking' of different types of lipids obtaining interesting information, but spiked samples do not represent a real-world situation as natively lipemic samples do.

METHODS

A total of 101 samples flagged as 'lipemic' by a Sysmex CS-5100 coagulometer were analyzed for PT, aPTT, fibrinogen Clauss assay, antithrombin activity, D-dimer concentration, before and after a double high-speed centrifugation procedure to reduce lipemic interference. We evaluated using Bland-Altman test if high-speed centrifugation and retesting are justified, considering that's a resource-consuming procedure; when a statistically significant difference was found, quality specification for imprecision was considered and compared to the observed delta.

RESULTS

Statistically significant differences were found for PT, antithrombin activity and fibrinogen. Considering the Bland-Altman plot, fibrinogen results were split into two groups, and statistically significant difference was confirmed only for samples >2 g/L.

CONCLUSIONS

For PT and antithrombin activity a mean percentual difference between the two determinations lower than within-subject biologic variation and one of the Fraser's quality specifications can be considered as a confounding 'noise' factor that is neither analytically nor clinically relevant. If the instrument determines a result on the first run, for PT, aPTT, D-dimer concentration and antithrombin activity tests, the double plasma high-speed centrifugation is unnecessary. It is instead necessary if fibrinogen >2 g/L or if the instrument cannot determine a result on the first run.

Pre-analytical practices for routine coagulation tests in European laboratories. A collaborative study from the European Organisation for External Quality Assurance Providers in Laboratory Medicine (EQALM)

Background

Correct handling and storage of blood samples for coagulation tests are important to assure correct diagnosis and monitoring. The aim of this study was to assess the pre-analytical practices for routine coagulation testing in European laboratories.

Methods

In 2013–2014, European laboratories were invited to fill in a questionnaire addressing pre-analytical requirements regarding tube fill volume, citrate concentration, sample stability, centrifugation and storage conditions for routine coagulation testing (activated partial thromboplastin time [APTT], prothrombin time in seconds [PT-sec] and as international normalised ratio [PT-INR] and fibrinogen).

Results

A total of 662 laboratories from 28 different countries responded. The recommended 3.2% (105–109 mmol/L) citrate tubes are used by 74% of the laboratories. Tube fill volumes ≥90% were required by 73%–76% of the laboratories, depending upon the coagulation test and tube size. The variation in centrifugation force and duration was large (median 2500 g [10- and 90-percentiles 1500 and 4000] and 10 min [5 and 15], respectively). Large variations were also seen in the accepted storage time for different tests and sample materials, for example, for citrated blood at room temperature the accepted storage time ranged from 0.5–72 h and 0.5–189 h for PT-INR and fibrinogen, respectively. If the storage time or the tube fill requirements are not fulfilled, 72% and 84% of the respondents, respectively, would reject the samples.

Conclusions

There was a large variation in pre-analytical practices for routine coagulation testing in European laboratories, especially for centrifugation conditions and storage time requirements.

Level of agreement between laboratory and point-of-care prothrombin time in patients after stopping or continuation of acenocoumarol anticoagulation: A comparison of diagnostic accuracy

BACKGROUND

Procedures requiring optimisation of the coagulation status of patients using vitamin K antagonists are frequently postponed due to the late availability of laboratory international normalised ratio (INR) test results. A point-of-care (POC) alternative may facilitate early decision-making in peri-operative patients.

OBJECTIVES

To assess the level of agreement between the POC-INR and the laboratory INR in patients who continue or stop vitamin K antagonists to determine whether the POC test may be a good alternative to the laboratory INR.

DESIGN

Study of diagnostic accuracy.

SETTING

Single-centre study at Zaans Medical Centre, The Netherlands.

PATIENTS

Included patients were scheduled for cardioversion (these continued taking vitamin K antagonists), or a surgical procedure (these stopped taking vitamin K antagonists).

MAIN OUTCOME MEASURES

The level of agreement and clinical acceptability of the laboratory and POC-INR results, evaluated by Bland-Altman analysis and error grid analysis.

RESULTS

The surgical and cardioversion groups consisted of 47 and 46 patients, respectively. The bias in the INR in the surgical group was -0.12 ± 0.09 with limits of agreement of -0.29 to 0.05, whereas the cardioversion group showed a bias in the INR of -0.22 ± 0.36 with limits of agreement from -0.93 to 0.48. The percentage errors between methods in the surgical and cardioversion groups were 16 and 21%, respectively. Error grid analysis showed that the diagnostic accuracy of the POC prothrombin time is clinically acceptable as the difference did not lead to a different clinical decision in the surgical group with INR values less than 1.8.

CONCLUSION

The current study shows a good level of agreement and clinical accuracy between the laboratory and POC-INR in patients who stopped anticoagulation intake for surgery. However, in patients who continued their anticoagulation therapy, the agreement between the two methods was less accurate.

Influence of centrifugation conditions on the results of 77 routine clinical chemistry analytes using standard vacuum blood collection tubes and the new BD-Barricor tubes

Introduction

Although centrifugation is performed in almost every blood sample, recommendations on duration and g-force are heterogeneous and mostly based on expert opinions. In order to unify this step in a fully automated laboratory, we aimed to evaluate different centrifugation settings and their influence on the results of routine clinical chemistry analytes.

Materials and methods

We collected blood from 41 healthy volunteers into BD Vacutainer PST II-heparin-gel- (LiHepGel), BD Vacutainer SST II-serum-, and BD Vacutainer Barricor heparin-tubes with a mechanical separator (LiHepBar). Tubes were centrifuged at 2000xg for 10 minutes and 3000xg for 7 and 5 minutes, respectively. Subsequently 60 and 21 clinical chemistry analytes were measured in plasma and serum samples, respectively, using a Roche COBAS instrument.

Results

High sensitive Troponin T, pregnancy-associated plasma protein A, ß human chorionic gonadotropin and rheumatoid factor had to be excluded from statistical evaluation as many of the respective results were below the measuring range. Except of free haemoglobin (fHb) measurements, no analyte result was altered by the use of shorter centrifugation times at higher g-forces. Comparing LiHepBar to LiHepGel tubes at different centrifugation setting, we found higher lactate-dehydrogenase (LD) (P = 0.003 to < 0.001) and lower bicarbonate values (P = 0.049 to 0.008) in the latter.

Conclusions

Serum and heparin samples may be centrifuged at higher speed (3000xg) for a shorter amount of time (5 minutes) without alteration of the analytes tested in this study. When using LiHepBar tubes for blood collection, a separate LD reference value might be needed.

Preanalytical Issues in Hemostasis and Thrombosis Testing

Hemostasis testing is critical to many hemorrhagic and thrombotic disorders, wherein laboratory diagnostics can provide critical information for diagnosis, prognostication, and therapeutic monitoring. Due to this crucial role in modern medicine, hemostasis tests should be carried out at their highest degree of quality, thus encompassing standardization and monitoring of all phases of the testing process. It is now clearly established that the preanalytical phase is the most critical and vulnerable part of the total testing process, since up to 70% of diagnostic errors are due to highly manual activities encompassing patient preparation and collection of biological samples, as well as handling, transportation, preparation and storage of blood specimens. Due to the peculiar sample matrix required for hemostasis testing (i.e., plasma anticoagulated with buffered sodium citrate), additional critical issues may impair the reliability of these tests. Therefore, this article aims to provide an updated overview of the most important preanalytical variables that may ultimately impair the quality of hemostasis and thrombosis testing.

Pre-analytical issues in the haemostasis laboratory: guidance for the clinical laboratories

Ensuring quality has become a daily requirement in laboratories. In haemostasis, even more than in other disciplines of biology, quality is determined by a pre-analytical step that encompasses all procedures, starting with the formulation of the medical question, and includes patient preparation, sample collection, handling, transportation, processing, and storage until time of analysis. This step, based on a variety of manual activities, is the most vulnerable part of the total testing process and is a major component of the reliability and validity of results in haemostasis and constitutes the most important source of erroneous or un-interpretable results. Pre-analytical errors may occur throughout the testing process and arise from unsuitable, inappropriate or wrongly handled procedures. Problems may arise during the collection of blood specimens such as misidentification of the sample, use of inadequate devices or needles, incorrect order of draw, prolonged tourniquet placing, unsuccessful attempts to locate the vein, incorrect use of additive tubes, collection of unsuitable samples for quality or quantity, inappropriate mixing of a sample, etc. Some factors can alter the result of a sample constituent after collection during transportation, preparation and storage. Laboratory errors can often have serious adverse consequences. Lack of standardized procedures for sample collection accounts for most of the errors encountered within the total testing process. They can also have clinical consequences as well as a significant impact on patient care, especially those related to specialized tests as these are often considered as "diagnostic". Controlling pre-analytical variables is critical since this has a direct influence on the quality of results and on their clinical reliability. The accurate standardization of the pre-analytical phase is of pivotal importance for achieving reliable results of coagulation tests and should reduce the side effects of the influence factors. This review is a summary of the most important recommendations regarding the importance of pre-analytical factors for coagulation testing and should be a tool to increase awareness about the importance of pre-analytical factors for coagulation testing.

Pre-analytic variability in cardiovascular biomarker testing

The impact of laboratory medicine on clinical cardiology has dramatically increased over the years and a lot of cardiovascular biomarkers have been recently proposed. In order to avoid clinical mistakes, physicians should be well aware of all the aspects, which could affect the quality of laboratory results, remembering that pre-analytic variability is an often overlooked significant source of bias, determining the vast majority of laboratory errors. This review addresses the determinants of pre-analitycal variability in cardiovascular biomarker testing, focusing on the most widespread biomarkers, which are cardiac troponins and natriuretic peptides.

Plasma centrifugation does not influence thrombin-antithrombin and plasmin-antiplasmin levels but determines platelet microparticles count

Introduction

Centrifugation is an essential step for plasma preparation to remove residual elements in plasma, especially platelets and platelet-derived microparticles (PMPs). Our working hypothesis was that centrifugation as a preanalytical step may influence some coagulation parameters.

Materials and methods

Healthy young men were recruited (N = 17). For centrifugation, two protocols were applied: (A) the first centrifugation at 2500 x g for 15 min and (B) at 2500 x g for 20 min at room temperature with a light brake. In protocol (A), the second centrifugation was carried out at 2500 x g for 15 min, whereas in protocol (B), the second centrifugation involved a 10 min spin at 13,000 x g. Thrombin-antithrombin (TAT) and plasmin-antiplasmin (PAP) complexes concentrations were determined by enzyme-linked immunosorbent assays. PMPs were stained with CD41 antibody and annexin V, and analyzed by flow cytometry method. Procoagulant activity was assayed by the Calibrated Automated Thrombogram method as a slope of thrombin formation (CAT velocity).

Results

Median TAT and PAP concentrations did not differ between the centrifugation protocols. The high speed centrifugation reduced the median (IQR) PMP count in plasma from 1291 (841-1975) to 573 (391-1010) PMP/µL (P = 0.001), and CAT velocity from 2.01 (1.31-2.88) to 0.97 (0.82-1.73) nM/min (P = 0.049). Spearman’s rank correlation analysis showed correlation between TAT and PMPs in the protocol A plasma which was (rho = 0.52, P < 0.050) and between PMPs and CAT for protocol A (rho = 0.74, P < 0.050) and protocol B (rho = 0.78, P < 0.050).

Conclusion

Centrifugation protocols do not influence the markers of plasminogen (PAP) and thrombin (TAT) generation but they do affect the PMP count and procoagulant activity.

Design and Analysis for Studying microRNAs in Human Disease: A Primer on -Omic Technologies

microRNAs (miRNAs) are fundamental to cellular biology. Although only approximately 22 bases long, miRNAs regulate complex processes in health and disease, including human cancer. Because miRNAs are highly stable in circulation when compared with several other classes of nucleic acids, they have generated intense interest as clinical biomarkers in diverse epidemiologic studies. As with other molecular biomarker fields, however, miRNA research has become beleaguered by pitfalls related to terminology and classification; procedural, assay, and study cohort heterogeneity; and methodological inconsistencies. Together, these issues have led to both false-positive and potentially false-negative miRNA associations. In this review, we summarize the biological rationale for studying miRNAs in human disease with a specific focus on circulating miRNAs, which highlight some of the most challenging topics in the field to date. Examples from lung cancer are used to illustrate the potential utility and some of the pitfalls in contemporary miRNA research. Although the field is in its infancy, several important lessons have been learned relating to cohort development, sample preparation, and statistical analysis that should be considered for future studies. The goal of this primer is to equip epidemiologists and clinical researchers with sound principles of study design and analysis when using miRNAs.

Design and establishment of a biobank in a multicenter prospective cohort study of elderly patients with venous thromboembolism (SWITCO65+)

In the field of thrombosis and haemostasis, many preanalytical variables influence the results of coagulation assays and measures to limit potential results variations should be taken. To our knowledge, no paper describing the development and maintenance of a haemostasis biobank has been previously published. Our description of the biobank of the Swiss cohort of elderly patients with venous thromboembolism (SWITCO65+) is intended to facilitate the set-up of other biobanks in the field of thrombosis and haemostasis. SWITCO65+ is a multicentre cohort that prospectively enrolled consecutive patients aged ≥65 years with venous thromboembolism at nine Swiss hospitals from 09/2009 to 03/2012. Patients will be followed up until December 2013. The cohort includes a biobank with biological material from each participant taken at baseline and after 12 months of follow-up. Whole blood from all participants is assayed with a standard haematology panel, for which fresh samples are required. Two buffy coat vials, one PAXgene Blood RNA System tube and one EDTA-whole blood sample are also collected at baseline for RNA/DNA extraction. Blood samples are processed and vialed within 1 h of collection and transported in batches to a central laboratory where they are stored in ultra-low temperature archives. All analyses of the same type are performed in the same laboratory in batches. Using multiple core laboratories increased the speed of sample analyses and reduced storage time. After recruiting, processing and analyzing the blood of more than 1,000 patients, we determined that the adopted methods and technologies were fit-for-purpose and robust.

Laboratory reporting of hemostasis assays: the final post-analytical opportunity to reduce errors of clinical diagnosis in hemostasis?

The advent of modern instrumentation, with associated improvements in test performance and reliability, together with appropriate internal quality control (IQC) and external quality assurance (EQA) measures, has led to substantial reductions in analytical errors within hemostasis laboratories. Unfortunately, the reporting of incorrect or inappropriate test results still occurs, perhaps even as frequently as in the past. Many of these cases arise due to a variety of events largely outside the control of the laboratories performing the tests. These events are primarily preanalytical, related to sample collection and processing, but can also include post-analytical events related to the reporting and interpretation of test results. The current report provides an overview of these events, as well as guidance for prevention or minimization. In particular, we propose several strategies for the post-analytical reporting of hemostasis assays, and how this may provide the final opportunity to prevent serious clinical errors in diagnosis. This report should be of interest to both the laboratory scientists working in hemostasis and clinicians that request and attempt to interpret the test results. Laboratory scientists are ultimately responsible for these test results, and there is a duty to provide both accurate and precise results to enable clinicians to manage patients appropriately and to avoid the need to recollect and retest. Also, clinicians will not be in a position to best diagnose and manage their patient unless they gain an appreciation of these issues.