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Biological Variation of Hemostasis Variables in Thrombosis and Bleeding: Consequences for Performance Specifications.

In diagnostic testing, it is important to produce results that help the physicians in determining the diagnosis and optimal treatment of their patients. Measurements of hemostasis variables are frequently performed and the results are required for diagnosis of bleeding disorders (such as the von Willebrand disease of hemophilia) and for establishing the risk for thrombosis [such as increased factor VIII (FVIII)]. [3] The optimal approach for setting analytical performance criteria is still under development (1-3). Ideally, the performance criteria should be based on the demands of clinical outcome (4). However, the approach to define the analytical performance specifications using biological variation is currently seen as state-of-the-art (5, 6).

Biological variation is defined as the variation within individuals when they are measured repeatedly over time. This within-subject biological variation can be influenced by transient environmental and lifestyle factors such as stress (physical exercise), acute phase reactions, circadian rhythm, and seasonal variation (7-11). Other sources of variation in the analysis of hemostasis factors are the between-individual and the analytical variation of the assays.

To determine the criteria for the maximal allowable analytical variation for hemostasis parameters, data on biological variation can be used and this approach has been suggested to be the optimal method available (5, 6, 12). However, information on biological variation in hemostasis variables is still limited and is based on small studies with a limited number of sampling points, a short time period, and/or only specifically selected parameters (10, 13-21). To provide a recommendation based on biological variation, there is a need for a large study over a longer time period with sufficient sampling moments and comprehensive thrombosis and bleeding variables.

The aim of this study was to determine in a prolonged longitudinal study (i.e., 13 repeated blood sampling and measurements across a period of 1 year) the biological variation of hemostasis variables involved in thrombosis and bleeding [prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen, antithrombin (AT), protein C, protein S, factor VIII, factor IX, von Willebrand factor (VWF)]. On the basis of the biological variation obtained from this study we provide recommendations for analytical performance specifications for laboratory tests used for the diagnosis, follow-up, and monitoring of the treatment of thrombosis and bleeding. Additionally, we determine whether the performance of the hemostasis tests used in this study fulfils these new, predefined analytical criteria, based on biological variation.

Study Participants and Methods

STUDY POPULATION

Our study included 40 healthy individuals without symptoms of chronic or acute infectious diseases who had not undergone surgical procedures within the 3 months before their inclusion in the study. Blood was collected from each participant, at 13 visits over a 1-year time period. Data on demographics and cardiovascular risk factors were gathered using standardized questionnaires. Before each blood collection, study participants were asked whether they had recently used drugs, or suffered from infections, such as the common cold. The study protocol was in accordance with the Declaration of Helsinki and was approved by the Medical Ethics Committee of Erasmus MC. Written informed consent was obtained from each participant.

BLOOD SAMPLING PROCEDURE AND PLASMA

MEASUREMENTS

Blood was collected while the study participants were sitting and resting. They were allowed to have a light breakfast on the morning of blood collection. Blood was drawn by venipuncture using the Vacutainer system (Becton Dickinson) containing sodium citrate (final concentration 0.105 mol/L). Plasma was obtained by centrifugation at 3500g for 15 min at 4 [degrees]C and stored in aliquots at -80 [degrees]C until further analysis. On visual inspection, no plasma samples were lipemic, icteric, or hemolytic. All parameters tested in this study have been reported to be stable for up to 18 months when plasma is stored at -74 [degrees]C (22). To avoid interassay analytical variation, all samples from each participant were analyzed in 1 run.

ASSAYS

Routine coagulation tests (APTT, PT, fibrinogen) and coagulation inhibitors (antithrombin, protein C chromogenic and clotting activity, and protein S total and free antigen and clotting activity) were measured on an STA Compact analyzer using STAGO reagents (APTT: STA PTT Automate; PT: STA neoplastin CI; fibrinogen: STA fibrinogen; antithrombin: Stachrom AT; protein C chromogenic: Stachrom protein C; protein C clotting activity: Staclot protein C; protein S clotting activity: Staclot protein S; total protein S antigen: Liatest total protein S; free protein S antigen: Liatest free protein S) (Diagnostica Stago).

Von Willebrand factor antigen (VWF:Ag) concentrations were determined with an in-house ELISA assay, using polyclonal rabbit anti-human VWF antibodies (DakoCytomation) for capturing and detecting (23).

Von Willebrand factor collagen binding (VWF:CB) activity was measured by an in-house ELISA assay using bovine Achilles tendon collagen type I for capturing (Sigma-Aldrich) and polyclonal rabbit anti-human VWF antibodies (DakoCytomation) for detecting.

Von Willebrand factor ristocetin cofactor (VWF: RCo) activity was measured with an in-house assay in a aggregometer (Chronolog Aggregometer 490) that measures the rate of aggregation of platelets in the presence of VWF and ristocetin.

FVIII coagulant activity (FVIII:C) was measured using a 1-stage clotting assay and derived from (the prolongation of) the clotting time (APTT) measured with Triniclot (Kordia) on the Sysmex CA-1500 (Siemens).

Factor IX coagulant activity (FIX:C) was measured using a 1-stage clotting assay and derived from (the prolongation of) the clotting time (APTT) measured with Actin FS on the Sysmex CS2100i (Siemens).

All assays used commercial reference plasma (Unicalibrator, Stago or Normal reference plasma, Precision Biologic, Kordia) that was standardized against the WHO standard by the manufacturer.

All samples of each individual were measured in duplicate in the same analytical run. Since we aimed to analyze analytical variation, no criteria were defined for reanalysis on the basis of bad duplicates. Each analytical run included a normal and abnormal QC sample, evaluated by the Westgard criteria (24). All study participant samples were measured with the same batch of reagents. To access the between-run CVs for the assays used in this study see Table 1 in the Data Supplement that accompanies the online version of this article, at http://www.clinchem.org/content/vol62/issue12.

STATISTICAL ANALYSIS

Data are presented as mean and SD or medians with interquartile range for continuous variables, depending on their distribution, and as counts and percentages for categorical variables. The components of variation are given as CV. All measured values were included in the analysis.

In the present study, sources of variation were calculated using a random-effects model from a completely nested design with 2 factors using the NESTED procedure in version 9.2 of the statistical program SAS (25). In the nested model (proc nested data = "file"; classes individual sampling; var measurement; run), individuals and sampling occasions are entered as classes and duplicate measurements as variable. The output of the procedure then gives between-subject variance, within-subject variance nested within individuals, while the analytical variance is the error term in the model. The variances were assumed to be normally distributed.

We calculated the number of repeated measurements (m) that was needed to estimate with 95% probability a homeostatic setting point, which did not deviate more than 10% and 20% (p%) from its true value (26, 27):

m = [[1.96 X [([CV.sup.2.sub.A] + [CV.sup.2.sub.I]).sup.1/2]/p%].sup.2]. (1)

Here, [CV.sub.A] was the coefficient of analytical variation and [CV.sub.I] was the coefficient of within-subject biological variation. The recommended analytical variation for a diagnostic test was calculated as 58% of total variation of the study population. By this criterion, the analytical variation adds a maximum of 12% variation to the total test variability (12). The recommended analytical imprecision for monitoring was calculated as 50% of the within subject biological variation, according to which an assay adds a maximum of 10% variation to the total test variability (5). In addition, the recommended analytical bias was calculated, which indicated the difference between the expected measurement results and the estimated true value of the measured quantity as a result of assay error (6):

Bias < 0.25 X [([CV.sub.G] + [CV.sub.Iwithin-Subject]).sup.1/2]. (2)

[CV.sub.G] was the coefficient of between-subject biological variation and [CV.sub.I] was the coefficient of within-subject biological variation.

Analyses were performed on the whole group and on subgroups [with and without outliers (values outside the 3-SD range), by sex, excluding oral contraceptive users and excluding smokers]. Statistical analyses were performed with SPSS for Windows version 15 (SPSS Inc), and SAS version 9.2. A 2-sided P value <0.05 was considered statistically significant.

Results

Our study group of 40 healthy volunteers had a median age of 51 years (25%-75% range 26-54 years), 65% were female, of whom 9 (35%) used oral contraceptives (Table 1). The rates of use of aspirin and lipid-lowering medications were low (5% and 2.5%, respectively).

When the different components of the variation (between-, within-subject and analytical) were separated, the between-subject variation varied from 4.1% to 31.2%, the within-subject variation from 2.6% to 25.6% and the assay variation from 1.3% to 12.9% (for details see Table 2). For some of the hemostasis variables the within-subject and between-subject variation were very different, while for other tests these parameters were quite similar (Table 2).

In the diagnostic laboratory, repeated measurements can be used to reduce the influence of within-subject variation on the test result and thus improve the estimate of the real homeostatic value. When we calculated the number of repeated measurements that would be required to reduce the [CV.sub.I] to below 20%, for many of the assays [PT, APTT, protein C chromogenic (PC-chrom), protein S activity (PS-act), protein S total (PS-total), protein S free (PS-free), FIX:C, and AT] a single measurement would be sufficient. For fibrinogen, PC clotting (PC-clot) test, VWF:Ag, VWF:CB and VWF:RCo tests and FVIII:C it was necessary to perform multiple tests to reach this level of precision (Table 3). If we aimed to decrease the within-subject individual variation to below 10%, the number of measurements is still 1 for PT and antithrombin. For the other tests more measurements would be required to achieve this precision, and for VWF:CB, for example, 82 measurements would be needed to obtain an analytical variation below 10% (Table 3), but in daily routine this precision is not needed.

The recommended desired [CV.sub.A] for diagnostic purposes, based on biological variation, (5, 6) varied between 2.8% for the PT and 35.5% for the VWF:CB assay, and for monitoring of treatment or disease severity the recommended desired [CV.sub.A] varied between 1.3% for the PT and 20.7% for the VWF:CB assay (Table 4). In Fig. 1 these recommended [CV.sub.A] are compared with the actual [CV.sub.A] for the tests. All tests were found to satisfy these requirements for use in diagnosis, and most tests also fulfilled the requirements for monitoring. Only PC-clot and PS-act assays had slightly higher analytical variations. When literature data on desirable analytical variation for the hemostasis tests were used for this analysis, our conclusion that the tests fulfilled the criteria were confirmed, although large differences in reported variations were seen between the different studies (Table 5) (10, 12-20). The allowable analytical bias varied between 1.2% for the PT to 15.3% for the VWF:CB test (Table 3).

Discussion

In this study, we have shown that the analytical variation of routine hemostasis tests that are used in the diagnosis of thrombosis and bleeding problems (PT, APTT, fibrinogen, protein C, protein S, AT, and VWF assays) fulfills the criteria defined by the biological variation approach, both for diagnostic testing and for the monitoring of treatment. Only 2 assays, i.e., PC-clot and PS-act, just missed the criterion for monitoring.

Using biological variation in healthy individuals is currently considered to be the best available method to define analytical performance specifications for tests (4, 28). However, we realize that this approach has some limitations. Importantly, it does not take clinical relevance into consideration (4). Nevertheless, the use of the biological variation of hemostasis variables in healthy individuals provides a helpful tool for the diagnostic laboratory to set performance specifications (5, 6). The Dutch SKML external quality program has recently started to use biological variation in their assessment of quality.

In any laboratory, the central and most important aim is the quality of the measurement procedures and of the outcomes. To determine this quality, it is essential to define criteria. These were first discussed during the Stockholm Consensus Conference on analytical quality specifications (29). Recently, this consensus agreement was revisited during the first Strategic Conference on Analytical Quality Specifications organized by the European Federation for Laboratory Medicine (EFLM) (4, 28). The main outcome of the Conference was agreement on the hierarchy of models that can be used to set analytical quality specifications. In this hierarchy, only "evaluation of the effect of analytical performance on clinical outcomes in specific clinical settings" scores higher than "evaluating the effect of analytical performance using data based on components of biological variation," which makes the biological variation-based approach highly relevant for the clinical laboratory. Of course, evidence-based data on the requirements of different specific settings give the ultimate criteria for a diagnostic test.

The data that have been obtained on biological variation differ between studies. In many previous studies, assays were not performed in duplicate, preventing the differentiation of analytical variation from within- and between-individual variation. However, for most assays, analytical variation is much less than the within- and between-individual variation. Also the duration of the study may affect the data obtained on the biological variation. Several studies only consider the short-term biological variation (13, 20). Differences in study duration may account for differences in the desirable [CV.sub.A] based on these published short-term biological variation data and the data we obtained in our study (Table 4). The strength of our study is that the biological variation of general hemostatic variables (APTT, PT, Fibrinogen), markers for thrombotic (antithrombin, protein C, protein S) and bleeding (FVIII:C, FIX:C and VWF) disorders were measured in 1 study. In addition, the biological variation was established by sampling and measuring over a study period of 1 year thereby encompassing both short-term and long-term variation. A comparison of the findings of this study with those of the studies published in this field is summarized in Table 4. Our long-term study period includes any potential seasonal effects on the biological variation and as such a more reliable estimate of both the within- and between-individual biological variation.

We were able to isolate the analytical variation from the within- and between-variation because we measured our samples in duplicate. A component of analytical variation that is not isolated using this approach is the between-run variation that is part of the between-subject variation. In daily laboratory routine, samples from patients are measured on different days, so this type of variation in present in daily practice. For understanding how much between subject variation can be explained by analytical between-run variation we roughly calculated this component based on the internal QC results of our laboratory (see online Supplemental Table 1). For antithrombin (with relatively the highest internal QC CV) this between-run variation explains about half of the between-subject variation and still fulfils the imprecision criteria. For all other variables, the effect was very small (data not shown). Since we measured all samples of 1 patient in 1 run, this component does not contribute to the within-subject variation.

In the current study, we used only a single reagent on a single coagulation analyzer for each assay. Evaluation of data reported in the ECAT External Quality Assessment (EQA) program shows that variations within commercial diagnostic tests are of the same magnitude throughout different surveys but may differ between commercial diagnostic tests. Further studies on reagents and analyzers other than used in our study need to be performed before it is possible to ascertain whether our criteria are generalizable.

The participants of our study were between 21 and 70 years old and it is uncertain whether the conclusions of our study can be extrapolated to individuals who are younger or older.

The participants were allowed to have a light breakfast. We did not standardize the exact content of the breakfast, but it has been previously reported that a light breakfast either does not influence or only slightly influences laboratory coagulation tests (30). In our opinion, this reflects daily clinical practice in which patients are not always fasting when blood is drawn.

Analytical quality specifications based on the biological variation can also be used to assess whether the longterm analytical quality of laboratory testing based on the results in an EQA is sufficient (31, 32). Data on the biological variation obtained in this study may support the implementation of performance specifications both by laboratories and EQA programs. This may enable further improvement in diagnostic testing and the monitoring of treatment in thrombotic and bleeding disorders.

In conclusion, we have provided in this comprehensive study the analytical performance specifications for laboratory tests relevant in testing for thrombotic and bleeding disorders based on the data on biological variation. In addition, the reagents and analyzers used in this study ensure that the analytical performance of routine hemostasis tests fulfils these criteria.

Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.

Authors' Disclosures or Potential Conflicts of Interest: Upon manuscript submission, all authors completed the author disclosure form. Disclosures and/or potential conflicts of interest:

Employment or Leadership: C. Kluft, Good Biomarker Sciences; P. Meijer, ECAT Foundation.

Consultant or Advisory Role: C. Kluft, ECAT.

Stock Ownership: None declared.

Honoraria: None declared.

Research Funding: Unconditional gift of reagents from Diagnostica Stago (Ascieres surSeine, France); and the ECAT Foundation (Leiden, the Netherlands). C. Kluft, Good Biomarker Sciences.

Expert Testimony: None declared.

Patents: None declared.

Role of Sponsor: The funding organizations played no role in the design of study, choice of enrolled patients, review and interpretation of data, and final approval of manuscript.

Acknowledgments: J. Malfliet, F. van de Reijt, L. Felida, P. van Randwijk, and M. Dieterich (Dept, Hematology, Erasmus MC, Rotterdam, the Netherlands), and K. van Leuven andJ. Neuteboom (GBS, Leiden, the Netherlands) are acknowledged for their excellent laboratory assistance. Roche Diagnostics (Almere, the Netherlands) is acknowledged for their technical support.

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(32.) Meijer P, Kluft C, Haverkate F, De Maat MP. The longterm within- and between-laboratory variability for assay of antithrombin, and proteins C and S: results derived from the external quality assessment program for thrombophilia screening of the ECAT Foundation. J Thromb Haemost 2003; 1:748-53.

Moniek P.M. de Maat, [1] * Marianne van Schie, [1] Cornelis Kluft, [2] Frank W.G. Leebeek, [1] and Piet Meijer [2]

[1] Department of Haematology, Erasmus Medical Center, Rotterdam; [2] ECAT Foundation, Voorschoten, The Netherlands.

* Address correspondence to this author at: Dept. of Hematology (Rm. Nb845a), Erasmus University Medical Centre, PO Box 2040, 3000 CA Rotterdam, The Netherlands. Fax +31-10-4089470; e-mail m.demaat@erasmusmc.nl.

Received June 1, 2016; accepted August 17, 2016.

Previously published online at DOI: 10.1373/clinchem.2016.261248

[3] Nonstandard abbreviations: FVIII, factor VIII; PT, prothrombin time; APTT, activated partial thromboplastin time; AT, antithrombin; VWF, von Willebrand factor; VWF:Ag, VWF antigen; VWF:CB, VWF collagen binding; VWF:RCo, VWF ristocetin cofactor activity; FVIII:C, FVIII coagulant activity; FIX:C, FIX coagulant activity; PC-chrom, protein C chromogenic; PS-act, protein S activity; PS-total, protein S total; PS-free, protein S free; PC-clot, PC clotting; [CV.sub.A], analytical variation; [CV.sub.I], within-individual variation; CVG, between-individual variation; EFLM, European Federation for Laboratory Medicine; EQA, external quality assessment.

Caption: Fig. 1. Des red imprecision (monitoring and diagnostic) vs analytical [CV.sub.A]. Open columns indicate analytical variation; hatched columns, requirement for analytical variation in monitoring; and solid columns, requirement for analytical variation in diagnostictesting.
Table 1. Characteristics of the study population (n = 40).

Variable                                       Values

Age, years, median (range)                    51 (21-70)
Females, n (%)                                26 (65)
Smokers, n (%)                                 7 (18)
Body mass index, kg/[m.sup.2], mean (SD)    22.6 (2.0)
Oral contraceptives, n (%)                     9 (23)
Lipid lowering medication, n (%)               1 (2.5)
NSAIDs (aspirin), n (%)                        2 (5)

Table 2. Components of variation in plasma concentrations of
thrombophilia hemostasis variables.

                                                  CVs (%)

Variable             Mean (SD)     Between-subject   Within-subject

General assays
  PT, s              14.2 (0.7)          4.1               2.6
  APTT, s            36.1 (3.4)          7.1               6.4
  Fibrinogen, g/L    2.97(0.62)         17.0              11.9
Thrombosis factors
  AT, U/mL           1.10(0.09)          7.8               4.4
  PC-clot, U/mL      1.32 (0.29)        22.4               8.9
  PC-chrom, U/mL     1.19(0.25)         19.5               7.6
  PS-act, U/mL       0.91 (0.23)        23.8               8.1
  PS-total, U/mL     0.88 (0.17)        17.8               7.3
  PS-free, U/mL      0.94 (0.24)        25.0               7.6
Bleeding factors
  VWF:Ag, U/mL       1.11 (0.35)        28.6              15.8
  VWF:CB, U/mL       1.12 (0.49)        28.0              25.6
  VWF:RCo, U/mL      1.27(0.39)         31.2              21.3
  FVIII, U/mL        1.03 (0.30)        25.2              15.8
  FIX, U/mL          0.99 (0.20)        18.2               9.1

                           CVs (%)

Variable             Analytical variation

General assays
  PT, s                       1.3
  APTT, s                     1.4
  Fibrinogen, g/L             2.7
Thrombosis factors
  AT, U/mL                    1.4
  PC-clot, U/mL               5.5
  PC-chrom, U/mL              1.7
  PS-act, U/mL                4.1
  PS-total, U/mL              1.4
  PS-free, U/mL               3.3
Bleeding factors
  VWF:Ag, U/mL                4.2
  VWF:CB, U/mL               12.9
  VWF:RCo, U/mL               9.6
  FVIII, U/mL                 2.3
  FIX, U/mL                   2.8

Table 3. Recommendations for the number of repeated measurements and
analytical bias.

                     Number of repeated      Recommended
                     measurements to         analytical
                     reduce within-subject    bias (%)
                     variation to

Variable                10%         20%

General assays
  PT                     1           1           1.2
  APTT                   2           1           2.4
  Fibrinogen             6           2           5.2
Thrombosis factors
  AT                     1           1           1.3
  PC-clot                5           2           6.0
  PC-chrom               3           1           5.2
  PS-act                 4           1           6.3
  PS-total               3           1           4.8
  PS-free                3           1           6.5
Bleeding factors
  VWF:Ag                10           3           8.1
  VWF:CB                82          21           15.3
  VWF:RCo               21           5           9.4
  FVIII:C               10           3           7.4
  FIX:C                  4           1           5.1

Table 4. [CV.sub.A] as measured in this study in relation to the
recommended [CV.sub.A].

Variable             [CV.sub.A]:   Desirable [CV.sub.A]:
                     this                this study
                     study
                                   Diagnosis   Monitoring

General assays
  PT                     1.3          2.8         1.3

  APTT                   1.4          5.5         3.3

  Fibrinogen             2.7         12.0         6.0

Thrombosis factors
  AT                     1.4          5.2         2.2

  PC-clot                5.5         14.0         4.5

  PC-chrom               1.7         12.1         3.8

  PS-act                 4.1         14.6         4.0

  PS-total               1.4         11.1         3.7

  PS-free                3.3         15.2         3.8

Bleeding factors

  VWF:Ag                 4.2         18.9         7.9

  VWF:CB                12.9         35.5         20.7

  VWF:RCo                9.6         21.8         10.6

  FVIII:C                2.3         17.4         7.9

  FIX:C                  2.8         11.8         4.6

Variable                      Desirable [CV.sub.A]: literature
                                 data [references]

                     Diagnosis   Monitoring

General assays
  PT                  3.0-4.2    1.2-1.3 [Chen et al. (13), Dot et
                                 al. (14)]

  APTT                5.0-6.4    0.9-2.3 [Chen et al. (13), Dot et
                                 al. (14), Chamless et al. (15),
                                 Costongs et al. (21 )]

  Fibrinogen         10.0-13.5   2.6-6.7 [de Maat et al. (10), Chen
                                 et al. (13), Chamless et al. (15),
                                 Salomaa et al. (16)]

Thrombosis factors
  AT                  4.4-6.1    0.6-2.7 [Chamless et al. (15),
                                 Thompson et al. (17), Costongs et
                                 al. (21 )]

  PC-clot            7.8-11.1    1.2-4.0 [Chamless et al. (15), Wada
                                 et al. (18)]

  PC-chrom              --                       --

  PS-act               13.7      3.8 [Wada et al. (18)]

  PS-total              5.4      1.5 [Nguyen et al. (20)]

  PS-free               8.5      0.0 [Nguyen et al. (20)]

Bleeding factors

  VWF:Ag               15.5      7.2 [Kilercik et al. (19)]

  VWF:CB                --                       --

  VWF:RCo              11.7      4.1 [Kilercik et al. (19)]

  FVIII:C            11.4-15.4   2.4-8.0 [Chen et al. (13), Chamless
                                 et al. (15), Thompson et al. (17)]

  FIX:C                 7.2      3.0 [Chen et al. (13)]

Table 5. Overview of studies on biological variation in coagulation
parameters.

Reference                Number of      M/F      Study     Number of
                           study        (a)     period     sampling
                        participants                       occasions

This study                       40    14/26   1 year         13

Chen et al. (13)                 31    18/13   5 days          9

Nguyen et al. (20)               39    16/23   3-6 weeks       3

Dot et al. (14)                  39    20/19   9 months        9

Chamless et al. (15)             39    16/23   3-6 weeks       3

De Maat et al. (10)              20    10/10   6 months        9

Salomaa et al. (16)             473            3 years         2

Thompson et al. (17)             14     6/8    3 years        20

Wada et al. (18)                 17     8/9    1 year         12

Kilercik et al. (19)             19    10/9    5 weeks       15-19

Reference                                Parameters

This study              APTT, PT, Fbg, (b) ATIII, protein C clotting
                        and chromogenic activity, protein S activity,
                        total and free antigen, VWF antigen,
                        activity, collagen-binding, FVIII, FIX

Chen et al. (13)        APTT, PT, INR, Fbg, TT, FDP, FII, FV, FVII,
                        FVIII, FIX, FX, FXI, FXII

Nguyen et al. (20)      PAI-1, t-PA, D-Dimer, FPA, protein S total
                        and free

Dot et al. (14)         APTT, PT

Chamless et al. (15)    APTT, Fbg, ATIII, protein C, VWF:Ag, FVII,
                        FVIII

De Maat et al. (10)     Fbg, tPA:Ag, PAI-1 activity, CRP

Salomaa et al. (16)     Fbg, Plg, FVII

Thompson et al. (17)    Fbg, FII, FVII, FVIII, FX, VWF, ATIII,

Wada et al. (18)        APTT, PT, Fbg, thrombotest, ATIII,
                        [alpha]2PI, Plg, TAT, PAP, TM, PAI-1/tPA
                        complex, protein C and protein S

Kilercik et al. (19)    VWF antigen and activity, ADAMTS13 activity
                        and antigen

(a) M/F, number of males and females, respectively.

(b) Fbg, fibrinogen; ATIII, antithrombin III; INR, international
normalized ratio; TT, thrombin time; FDP, fibrin degradation product;
FII, factor II; FV, factor V; FVII, factor VII; FX, factor X; FXI,
factor XI; FXII, factor XII; PAI-1, plasminogen activator inhibitor-
1; tPA, tissue plasminogen activator; FPA, fibrinopeptide A; tPA:Ag,
tPA antigen; CRP, C-reactive protein; Plg, plasminogen; [alpha]2PI,
[[alpha].sub.2]-antiplasmin; TAT,thrombin-antithrombin; PAP, plasmin-
[alpha] 2-antiplasmin complex; TM,thrombomodulin; ADAMTS13, a
disintegrin and metalloproteinase with thrombospondin motifs 13.
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Title Annotation:Hemostasis and Thrombosis
Author:de Maat, Moniek P.M.; van Schie, Marianne; Kluft, Cornelis; Leebeek, Frank W.G.; Meijer, Piet
Publication:Clinical Chemistry
Article Type:Clinical report
Date:Dec 1, 2016
Words:5350
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