Estimates of Within-Subject Biological Variation of Protein C, Antithrombin, Protein S Free, Protein S Activity, and Activated Protein C Resistance in Pregnant Women

Concentration-effect relationship for tranexamic acid inhibition of tissue plasminogen activator-induced fibrinolysis in vitro using the viscoelastic ClotPro® TPA-test

BACKGROUND

Tranexamic acid is an antifibrinolytic drug that is commonly administered for obstetric haemorrhage. Conventional viscoelastic tests are not sensitive to tranexamic acid, but the novel ClotPro® TPA-test can measure tranexamic acid-induced inhibition of fibrinolysis. We aimed to evaluate the TPA-test in pregnant and non-pregnant women.

METHODS

We performed an in vitro study of whole blood samples spiked with tranexamic acid from pregnant women in the first, second, and third trimester (n=20 per group) and from non-pregnant women (n=20). We performed ClotPro TPA-tests of whole blood sample and ClotPro EX-tests, FIB-tests, and TPA-tests.

RESULTS

Clot lysis was inhibited in a concentration-dependent manner up to a tranexamic acid concentration of 6.25 mg L-1. At tranexamic acid concentrations of 12.5 mg L-1 and above, clot lysis was completely inhibited. The concentration-effect relationship of tranexamic acid did not differ in a clinically important manner in blood from pregnant women across all three trimesters or from non-pregnant controls. A median maximum lysis cut-off value of at9 least 16% (25-75th percentiles 15-18), a median clot lysis time of 3600 s (25-75th percentiles 3600-3600), or both was associated with a tranexamic acid concentration of least 12.5 mg L-1.

CONCLUSIONS

The ClotPro® TPA-test is sensitive in detecting inhibition of fibrinolysis by tranexamic acid in whole blood samples of pregnant and non-pregnant women. The concentration-effect relationship of tranexamic acid to inhibit fibrinolysis in whole blood did not differ for women in the first, second, and third trimester or for non-pregnant women.

Trimester-specific reference intervals of hemostasis biomarkers for healthy pregnancy

Physiological changes in hemostasis during pregnancy have been reported by several authors. This study aimed at establishing reference intervals for the hemostasis biomarkers thrombin-antithrombin complex (TAT), α2-plasmininhibitor-plasmin complex (PIC), thrombomodulin (TM) and tissue plasminogen activator-inhibitor complex (tPAI-C), in healthy pregnancies. After excluding outliers, a total of 496 healthy pregnant women (128 first-trimester, 142 second-trimester, 107 third-trimester and 119 pre-labor) and 103 healthy nonpregnant women were enrolled from Shenzhen Bao'an Women's and Children's Hospital. Hemostasis biomarkers, TAT, PIC, TM and tPAI-C, were measured by using a quantitative chemiluminescence enzyme immunoassay performed on HISCL automated analysers. The median and reference intervals (the 2.5th and 97.5th percentiles) were calculated to establish trimester-specific reference intervals for healthy pregnant women. The reference intervals for TAT, PIC, TM and tPAI-C in the first trimester were 0.7-7.6 1 µg/L, 0.2-0.9 mg/L, 2.8-11.0 TU/ml, and 1.2-6.5 1 µg/L, respectively. The reference intervals in the second trimester were 1.7-12.0 1 µg/L, 0.2-1.0 mg/L, 3.7-11.6 TU/ml, and 2.8-8.8 1 µg/L, respectively. The reference intervals in the third trimester were 2.7-16.1 1 µg/L, 0.1-1.4 mg/L, 2.9-12.9 TU/ml, and 1.9-8.0 1 µg/L, respectively. At pre-labor, the reference intervals were 4.8-32.9 1 µg/L, 0.2-1.9 mg/L, 4.2-12.6 TU/ml, and 2.8-15.4 1 µg/L, respectively. Gestational reference intervals for TAT, PIC, TM and tPAI-C in healthy pregnancies are provided, but only for TAT with increasing concentrations throughout pregnancy, the reference intervals for non-pregnant were not applicable.

Systematic review and meta-analysis of within-subject and between-subject biological variation data of coagulation and fibrinolytic measurands

OBJECTIVES

The diagnosis and monitoring of bleeding and thrombotic disorders depend on correct haemostatic measurements. The availability of high-quality biological variation (BV) data is important in this context. Many studies have reported BV data for these measurands, but results are varied. The present study aims to deliver global within-subject (CVI) and between-subject (CVG) BV estimates for haemostasis measurands by meta-analyses of eligible studies, by assessment with the Biological Variation Data Critical Appraisal Checklist (BIVAC).

METHODS

Relevant BV studies were graded by the BIVAC. Weighted estimates for CVI and CVG were obtained via meta-analysis of the BV data derived from BIVAC-compliant studies (graded A-C; whereby A represents optimal study design) performed in healthy adults.

RESULTS

In 26 studies BV data were reported for 35 haemostasis measurands. For 9 measurands, only one eligible publication was identified and meta-analysis could not be performed. 74% of the publications were graded as BIVAC C. The CVI and CVG varied extensively between the haemostasis measurands. The highest estimates were observed for PAI-1 antigen (CVI 48.6%; CVG 59.8%) and activity (CVI 34.9%; CVG 90.2%), while the lowest were observed for activated protein C resistance ratio (CVI 1.5%; CVG 4.5%).

CONCLUSIONS

This study provides updated BV estimates of CVI and CVG with 95% confidence intervals for a wide range of haemostasis measurands. These estimates can be used to form the basis for analytical performance specifications for haemostasis tests used in the diagnostic work-up required in bleeding- and thrombosis events and for risk assessment.

The Diagnostics and Treatment of Recurrent Pregnancy Loss

Recurrent pregnancy loss is a common problem in the reproductive age population of women. It can be caused by many different conditions. This problem is addressed in international guidelines that take a slightly different approach to its diagnosis and treatment. The guidelines used in this review mainly use the guidelines of the Royal College of Obstetricians and Gynaecologists (RCOG), American Society of Reproductive Medicine (ASRM) and European Society of Human Reproduction and Embryology (ESHRE). This review shows how much the approach to miscarriages has changed and how much more needs to be explored and refined. The review also addresses the topic of unexplained pregnancy loss, which continues to be a challenge for clinicians.

Biological variation: recent development and future challenges

Biological variation (BV) data have many applications in laboratory medicine. However, these depend on the availability of relevant and robust BV data fit for purpose. BV data can be obtained through different study designs, both by experimental studies and studies utilizing previously analysed routine results derived from laboratory databases. The different BV applications include using BV data for setting analytical performance specifications, to calculate reference change values, to define the index of individuality and to establish personalized reference intervals. In this review, major achievements in the area of BV from last decade will be presented and discussed. These range from new models and approaches to derive BV data, the delivery of high-quality BV data by the highly powered European Biological Variation Study (EuBIVAS), the Biological Variation Data Critical Appraisal Checklist (BIVAC) and other standards for deriving and reporting BV data, the EFLM Biological Variation Database and new applications of BV data including personalized reference intervals and measurement uncertainty.

Reference intervals for coagulation parameters in non-pregnant and pregnant women

Established reference intervals (RIs) of coagulation parameters generally based on the general population are not applicable to specific women. In order to accurately evaluate the coagulation status of non-pregnant women and pregnant women, specific RIs should be established. Our study recruited 465 non-pregnant women and 1972 pregnant women aged 20–45 years. Eight tests including antithrombin (AT), protein C (PC), free protein S (fPS), lupus anticoagulant (LA), D-dimer, fibrin/fibrinogen degradation products (FDP), coagulation factor VII (FVII), and factor VIII (FVIII) were performed on ACL TOP automated coagulation instrument. The RIs for these tests were established in non-pregnant and pregnant women at different gestational weeks. Compared to the non-pregnant group, the medians of AT and fPS were lower, while the medians of PC, LA normalized ratio, D-dimer, FDP, FVII, and FVIII were higher. During pregnancy, AT and fPS activity showed a decreasing trend, with the increase of gestational age. PC activity, LA normalized ratio, D-dimer concentrations, FDP concentrations, FVII, and FVIII activity presented an increasing trend, with the increase of gestational age. The non-pregnant women-specific RIs and the gestational age-specific RIs of AT, PC, fPS, LA normalized ratio, D-dimer, FDP, FVII, and FVIII needed to be established for accurate clinical diagnoses.

Long-term within- and between-subject biological variation of 29 routine laboratory measurands in athletes

OBJECTIVES

Within- and between-subject biological variation (BV) estimates have many applications in laboratory medicine. However, robust high-quality BV estimates are lacking for many populations, such as athletes. This study aimed to deliver BV estimates of 29 routine laboratory measurands derived from a Biological Variation Data Critical Appraisal Checklist compliant design in a population of high-endurance athletes.

METHODS

Eleven samples per subject were drawn from 30 triathletes monthly, during a whole sport season. Serum samples were measured in duplicate for proteins, liver enzymes, lipids and kidney-related measurands on an Advia2400 (Siemens Healthineers). After outlier and homogeneity analysis, within-subject (CV_I) and between-subject (CV_G) biological variation estimates were delivered (CV-ANOVA and log-ANOVA, respectively) and a linear mixed model was applied to analyze the effect of exercise and health related variables.

RESULTS

Most CV_I estimates were similar or only slightly higher in athletes compared to those reported for the general population, whereas two- to three-fold increases were observed for amylase, ALT, AST and ALP. No effect of exercise and health related variables were observed on the CV_I estimates. For seven measurands, data were not homogeneously distributed and BV estimates were therefore not reported.

CONCLUSIONS

The observation of higher CV_I estimates in athletes than what has been reported for the general population may be related to physiological stress over time caused by the continuous practice of exercise. The BV estimates derived from this study could be applied to athlete populations from disciplines in which they exercise under similar conditions of intensity and duration.

Comparability of sample results and commutability of reference materials among different measurement procedures for protein C activity assays

BACKGROUND AND AIMS

Several types of measurement procedures (MPs) for protein C activity assays are currently available. Clinical sample (CS) results among different MPs should be comparable. The commutability of reference materials (RMs) is an essential requirement to achieve comparability of CS results.

MATERIALS AND METHODS

Considering the total error calculated using reliable biological variation (BV) data and external quality assessment (EQA) criteria, we chose the allowable limits of comparability and criterion of commutability. According to Clinical and Laboratory Standardization Institute EP9 and our previous studies, 92 CSs were used to evaluate the comparability among the three MPs (Sysmex CS-5100, IL ACL TOP 700, and STA-R Evolution). The difference in bias method recommended by International Federation of Clinical Chemistry and Laboratory Medicine was used to assess the commutability of six RMs, including World Health Organization (WHO) IS 02/342.

RESULTS

The compliance rates of CSs were 94.6-100% with the corresponding calibration mode. WHO IS, HemosIL calibration plasma, and candidate RMs, PC20201 and PC20202, were commutable between each pair of the three MPs.

CONCLUSION

It is feasible to set the allowable limits of comparability and the criterion of commutability based on the BV and EQA criteria.

Management of recurrent miscarriages: an overview of current evidence

PURPOSE OF REVIEW

Recurrent miscarriage (RM) or recurrent pregnancy loss (RPL) is defined as the consecutive loss of two or more pregnancies before the age of viability. The exact prevalence of RM is unknown, but it has been reported between 1% and 2%. The objective of this review is to provide a critical summary of the latest evidence for the investigation and management of women with RM.

RECENT FINDINGS

RMs are associated with multiple factors including increased female age and lifestyle habits, as well as genetic factors, hereditary and acquired thrombophilia and infections. Metabolic and endocrine factors, in addition to anatomical causes such as uterine malformations have also been suggested as a causative factors of RM.

SUMMARY

The management of RM would be expected to cause specific, however, in the majority of the cases no cause is identified, and the factors associated with RM may not be causally related with the condition.

The European Biological Variation Study (EuBIVAS): Biological Variation Data for Coagulation Markers Estimated by a Bayesian Model

BACKGROUND

For biological variation (BV) data to be safely used, data must be reliable and relevant to the population in which they are applied. We used samples from the European Biological Variation Study (EuBIVAS) to determine BV of coagulation markers by a Bayesian model robust to extreme observations and used the derived within-participant BV estimates [CVP(i)] to assess the applicability of the BV estimates in clinical practice.

METHOD

Plasma samples were drawn from 92 healthy individuals for 10 consecutive weeks at 6 European laboratories and analyzed in duplicate for activated partial thromboplastin time (APTT), prothrombin time (PT), fibrinogen, D-dimer, antithrombin (AT), protein C, protein S free, and factor VIII (FVIII). A Bayesian model with Student t likelihoods for samples and replicates was applied to derive CVP(i) and predicted BV estimates with 95% credibility intervals.

RESULTS

For all markers except D-dimer, CVP(i) were homogeneously distributed in the overall study population or in subgroups. Mean within-subject estimates (CVI) were <5% for APTT, PT, AT, and protein S free, <10% for protein C and FVIII, and <12% for fibrinogen. For APTT, protein C, and protein S free, estimates were significantly lower in men than in women ≤50 years.

CONCLUSION

For most coagulation markers, a common CVI estimate for men and women is applicable, whereas for APTT, protein C, and protein S free, sex-specific reference change values should be applied. The use of a Bayesian model to deliver individual CVP(i) allows for improved interpretation and application of the data.

The European Biological Variation Study (EuBIVAS): a summary report

Biological variation (BV) data have many important applications in laboratory medicine. Concerns about quality of published BV data led the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) 1st Strategic Conference to indicate need for new studies to generate BV estimates of required quality. In response, the EFLM Working Group on BV delivered the multicenter European Biological Variation Study (EuBIVAS). This review summarises the EuBIVAS and its outcomes. Serum/plasma samples were taken from 91 ostensibly healthy individuals for 10 consecutive weeks at 6 European centres. Analysis was performed by Siemens ADVIA 2400 (clinical chemistry), Cobas Roche 8000, c702 and e801 (proteins and tumor markers/hormones respectively), ACL Top 750 (coagulation parameters), and IDS iSYS or DiaSorin Liaison (bone biomarkers). A strict preanalytical and analytical protocol was applied. To determine BV estimates with 95% CI, CV-ANOVA after analysis of outliers, homogeneity and trend analysis or a Bayesian model was applied. EuBIVAS has so far delivered BV estimates for 80 different measurands. Estimates for 10 measurands (Non-HDL Cholesterol, S100-β protein, neuron-specific enolase, soluble transferrin receptor, intact fibroblast growth-factor-23, uncarboxylated-unphosphorylated matrix-Gla protein, human epididymis protein-4, free, conjugated and %free prostate-specific antigen), prior to EuBIVAS, have not been available. BV data for creatinine and troponin I were obtained using two analytical methods in each case. The EuBIVAS has delivered high-quality BV data for a wide range of measurands. The BV estimates are for many measurands lower than those previously reported, having an impact on the derived analytical performance specifications and reference change values.

The interrelationship between pregnancy, venous thromboembolism, and thyroid disease: a hypothesis-generating review

Pregnancy induces physiological changes that affect the risk of thrombosis and thyroid disease. In this hypothesis-generating review, the physiological changes in the coagulation system and in thyroid function during a normal pregnancy are described, and the incidence of venous thromboembolism (VTE) and thyroid disease in and after a pregnancy are compared and discussed. Furthermore, evidence regarding the association between thyroid disease and VTE in non-pregnant individuals is scrutinized. In conclusion, a normal pregnancy entails hormonal changes, which influence the onset of VTE and thyroid disease. Current evidence suggests an association between thyroid disease and VTE in non-pregnant individuals. This review proposes the hypothesis that maternal thyroid disease associates with VTE in pregnant women and call for future research studies on this subject. If an association exists in pregnant women specifically, such findings may have clinical implications regarding strategies for thyroid function testing and potential thromboprophylaxis in selected individuals.

The association between activated protein C ratio and Factor V Leiden are gender-dependent

Background The most common cause of activated protein C (aPC) resistance is a missense substitution (Arg506Gln), known as Factor V Leiden (FVL). Due to its low cost, many laboratories use the aPC ratio as a primary test with a unisex cut-off. However, the association between the aPC ratio and FVL including any relation to gender has been sparsely investigated. Methods Results of the aPC ratio and FVL analyses from 1081 patients referred to the Thrombophilia Clinic at Odense University Hospital were compared. Results In 153 FVL positive patients, the mean aPC ratio was 2.1 ± 0.3, which differed from 2.7 ± 0.4 in FVL negative individuals (p < 0.01). The receiver operating characteristics (ROC), with area under the curve (AUC) of 0.93, indicated the optimal aPC cut-off at 2.3-2.4, with sensitivity 89%-94%, specificity 71%-84%, positive predictive value 35%-48% and negative predictive value 98%-99%. In FVL positive females, the mean aPC ratio was 2.0 ± 0.3, which differed from males (2.1 ± 0.3, p < 0.05). In FVL negative females, the mean aPC ratio was 2.6 ± 0.4, also different from males (2.8 ± 0.5, p < 0.01). Of note, 35% of FVL negative females had an aPC ratio ≤2.4 against 18% in males (p < 0.01). Conclusions Our results indicate that the aPC ratio is lower in females than in males. Due to a high negative predictive value the aPC ratio can be used as a first line test for FVL, but those found positive must be confirmed with a DNA test.

Plasma Free Protein S Is Correlated with Disease Activity, but not with Subclinical Atherosclerosis among Patients with Systemic Lupus Erythematosus: A Cross-Sectional Study

A defect in clearance of apoptotic materials is pivotal in the pathogenesis of systemic lupus erythematosus (SLE). Protein S participates in the removal of apoptotic remnants and the anticoagulation pathway. The aim of the study was to clarify the relationship between plasma levels of free protein S and the disease activity or subclinical atherosclerosis in SLE. Free protein S was measured by an enzyme-linked immunosorbent assay, and patients were classified into two groups of free protein S levels: low (< 50%) and normal (≥ 50%). One hundred-eleven Korean female patients with SLE were enrolled, and the levels of free protein S were 67.4 ± 19.7%. Carotid plaque was detected in 25 (22.5%) patients. Twenty-one patients with low free protein S had lower hemoglobin (11.4 ± 1.4 vs. 12.5 ± 1.4 g/dL) and lymphocytes (1,221 ± 609 vs. 1,720 ± 1,097/µL), higher erythrocyte sedimentation rate (30.1 ± 20.6 vs. 20.8 ± 17.8 mm/h), and lower complement 3 (80.8 ± 27.6 vs. 103.4 ± 25.8 mg/dL) and complement 4 (15.6 ± 10.4 vs. 21.5 ± 7.6 mg/dL) than those with normal protein S. There was no significant difference in the proportion of patients with increased carotid artery intima-media thickness (> 4.6 mm) or with carotid artery plaque between two groups. The low levels of free protein S were associated with hemoglobin (OR = 0.64, p = 0.04) and complement 3 (OR = 0.96, p = 0.005). Free protein S is correlated with disease activity, but not with subclinical atherosclerosis in SLE.

Concentration of fibrin monomer in pregnancy and during the postpartum period

Background

D-dimer increases during pregnancy and is problematic to use in the diagnosis of venous thromboembolism. Fibrin monomer represents an alternative biomarker for venous thromboembolism. However, to be useful in pregnancy, the fibrin monomer concentration should be stable throughout pregnancy and during postpartum.

Methods

To describe the course of fibrin monomer concentration during pregnancy and the postpartum period in healthy pregnant women and to compare their within-subject biological variation (CVI) with non-pregnant women. Blood samples were obtained every fourth week during pregnancy and three samples after delivery in 20 healthy women and every fourth week during a 40-week period in 19 healthy non-pregnant women. Fibrin monomer (STA Liatest FM, Stago) was analysed in duplicates for all samples. Concentrations of fibrin monomer in pregnant and non-pregnant women were compared and the CVI for fibrin monomer was calculated.

Results

The median fibrin monomer concentration in pregnant women was 6.2 mg/L (2.5 and 97.5 percentiles 3.7–10.8 mg/L) and in non-pregnant women 4.8 mg/L (3.6–8.2) ( P < 0.01). The fibrin monomer concentration was relatively stable during pregnancy, although a few unexplained high fibrin monomer concentrations were found during pregnancy/postpartum. Fibrin monomer CVI in pregnancy and postpartum was 20.6% (95% CI 18.3, 23.5) and in non-pregnant 16.1% (13.7, 18.9).

Conclusions

For clinical purposes, fibrin monomer concentration can be considered stable during pregnancy, although it is slightly higher than in non-pregnant women. Pregnant and non-pregnant women have the same CVI. The suitability of fibrin monomer in venous thromboembolism diagnosis in pregnant women should be validated in further studies.

Within-subject biological variation of activated partial thromboplastin time, prothrombin time, fibrinogen, factor VIII and von Willebrand factor in pregnant women

Background:

During pregnancy, interpretation of results from coagulation parameters can be difficult as the physiological changes that occur may affect the biochemical parameters. The aim of this study was to describe the normal course of five coagulation parameters in healthy pregnancies, and to estimate the within-subject biological variation (CVI).

Methods:

Blood samples were obtained every 4th week during pregnancy and three samples after delivery in 20 healthy women and every 4th week during a 40-week period in 19 healthy non-pregnant women. Activated partial thromboplastin time (APTT), prothrombin time (PT), PT International Normalized Ratio (INR), fibrinogen, factor VIII clot (FVIII:C) and von Willebrand factor antigen (vWF:Ag) were analyzed. The physiological changes during pregnancy were compensated by transformation into multiples of the median (MoM) and it is natural logarithm (lnMoM) in order to establish a kind of steady state, and CVIwas calculated from the standard deviation.

Results:

During pregnancy, APTT, PT and INR remained unchanged or decreased, depending upon the reagent used, while fibrinogen, FVIII:C and vWF:Ag increased gradually until delivery. The CVIin pregnancy were 2.2 and 3.0% for APTT, 2.3 and 2.6% for PT, 2.2 and 2.3% for INR, 7.2% for fibrinogen, 12.2% for FVIII:C and 11.3% for vWF:Ag, and corresponded with the CVIin non-pregnant women.

Conclusions:

Transformation of coagulation parameters in healthy pregnancies to MoM is a tool to establish a kind of steady state. Although there is a physiological change in these coagulation parameters during pregnancy, the CVIafter lnMoM transformation was comparable with the CVIof non-pregnant women.