Comparative evaluation of reagents for measuring protein S activity: possibility of harmonization.

Patients with congenital protein S (PS) deficiency show a hereditary predisposition for thrombosis, and PS deficiency is prevalent among Japanese populations. Diagnosis is based on symptoms of thrombosis and reduced PS activity. Three reagents that use different measurement principles for determining PS activity are available in Japan. This study aimed to confirm the possibility of harmonization of these three reagents to establish a universal standard for PS activity in Japanese populations. Commercial normal plasma and plasma samples obtained from healthy individuals and healthy pregnant women were tested at three facilities using three reagents for measuring PS: STA-Staclot Protein S (STA-PS), HemosIL Protein S (Clotting) (IL-PS), and a total PS assay (SNT-PS). The within-run precision of each reagent was good, as each had a coefficient of variation of ≤ 3.8%. The dilution linearity for each reagent was also good. The correlation coefficient was 0.94 for STA-PS vs. IL-PS, 0.93 for SNT-PS vs. STA-PS, and 0.90 for SNT-PS vs. IL-PS, indicating a good correlation. Although the three reagents available in Japan for measuring PS activity use different measurement methods, each showed good performance, and large differences were not observed between the obtained values. Harmonization among them appears possible.

High Prevalence of Acquired Thrombophilia Without Prognosis Value in Patients With Coronavirus Disease 2019.

Background Recent literature reports a strong thrombotic tendency in patients hospitalized for a coronavirus disease 2019 (COVID-19) infection. This characteristic is unusual and seems specific to COVID-19 infections, especially in their severe form. Viral infections can trigger acquired thrombophilia, which can then lead to thrombotic complications. We investigate for the presence of acquired thrombophilia, which could participate in this phenomenon, and report its prevalence. We also wonder if these thrombophilias participate in the bad prognosis of severe COVID-19 infections. Methods and Results In 89 consecutive patients hospitalized for COVID-19 infection, we found a 20% prevalence of PS (protein S) deficiency and a high (ie, 72%) prevalence of antiphospholipid antibodies: mainly lupus anticoagulant. The presence of PS deficiency or antiphospholipid antibodies was not linked with a prolonged activated partial thromboplastin time nor with D-dimer, fibrinogen, or CRP (C-reactive protein) concentrations. These coagulation abnormalities are also not linked with thrombotic clinical events occurring during hospitalization nor with mortality. Conclusions We assess a high prevalence of positive tests detecting thrombophilia in COVID-19 infections. However, in our series, these acquired thrombophilias are not correlated with the severity of the disease nor with the occurrence of thrombotic events. Albeit the strong thrombotic tendency in COVID-19 infections, the presence of frequent acquired thrombophilia may be part of the inflammation storm of COVID-19 and should not systematically modify our strategy on prophylactic anticoagulant treatment, which is already revised upwards in this pathological condition. Registration URL: https://www.clini​caltr​ials.gov; Unique identifier: NCT04335162.

Compound heterozygous mutations identified in severe type I protein S deficiency impaired the secretion of protein S.

AIMS: Hereditary protein S (PS) deficiency is one of the natural anticoagulant deficiencies causing thrombophilia. We herein described a young male with recurrent deep venous thrombosis, who was diagnosed as type I PS deficiency with compound heterozygous mutations of PROS1 gene. We aimed to analyse the relationship between the genotype and phenotype detection and investigate the pathological mechanisms of PROS1 mutations causing PS deficiency. METHODS: Genetic analysis of PROS1 gene was carried out by direct sequencing. Thrombin generation potential and the inhibition function of thrombin generation by plasma PS were detected by thrombin generation test (TGT). The mRNA transcription level of mutant PS in vitro was measured by real-time PCR, while the protein level was evaluated by western blot and ELISA. Cellular distribution of the protein was further analysed by immunofluorescence. RESULTS: Compound heterozygous mutations (PROS1 c.1551_1552delinsG, p.Thr518Argfs*39 and PROS1 c.1681C>T, p.Arg561Trp) were identified in the propositus, and the former one was a novel small indel mutation. TGT results showed impaired inhibition of thrombin generation with the addition of activated protein C in his parents with certain heterozygous mutations. In vitro expression study, p.Thr518Argfs*39 mutant produced truncated protein retained in the cytoplasm, while p.Arg561Trp mutant partially affected the secretion of PS. Both mutations are located in C-terminal sex hormone-binding globulin (SHBG)-like domain of PS. CONCLUSIONS: Compound heterozygous mutations identified in the study have strong detrimental effect, causing severe type I PS deficiency in the propositus. SHBG-like domain of PS might play an important role in PS secretion system.

Protein C and protein S deficiencies may be related to survival among hemodialysis patients.

BACKGROUND: Thrombophilia due to protein C (PC) and protein S (PS) deficiencies is highly prevalent among patients with stage 5 chronic kidney disease and is reported to arise due to extracorporeal circulation during hemodialysis (HD). This study aimed to evaluate the relationship between HD treatment and thrombophilia. METHODS: A total of 114 Japanese patients on maintenance HD (62 men, 52 women) were followed during 2008-2011. Their survival rates were compared against the duration of HD. Prior to each HD, coagulation/fibrinolysis parameters and PC and PS activities were measured using standard techniques. The patients were divided into two groups: Group 1, with PC and/or PS deficiencies (n = 32), and Group 2, without PC and PS deficiencies (n = 82). The influence of such deficiencies and duration of dialysis on survival was examined. Time-to-event analysis was applied using Kaplan-Meier estimates, and the log-rank test was proposed to test the equivalence of relative survival data. Hazard ratios and 95% confidence intervals (CI) were calculated. RESULTS: Of the 114 patients, 37 died (Group 1, 22; Group 2, 15). The hazard ratio (95% CI) was higher (p = 0.004) in Group 1 than Group 2. Gene analyses of PC and PS were performed in 14 patients from Group 1. No mutations in either protein were observed. We analyzed the causes of death in both groups; however, the estimated thrombophilia-related incidence of death could not be determined due to small sample size of HD patients. CONCLUSIONS: Our results suggest that PC and PS deficiencies may be related to survival in HD patients. However, this finding warrants additional research.

New functional test for the TFPIα cofactor activity of Protein S working in synergy with FV-Short.

Essentials Protein S and FV-Short are synergistic cofactors to Tissue Factor Pathway Inhibitor α (TFPIα). An assay for the TFPIα synergistic cofactor activity of protein S with FV-Short was developed. The assay was specific for the synergistic TFPIα-cofactor activity of free protein S. Protein S deficient individuals with known mutations were correctly distinguished from controls. SUMMARY: Background Protein S is an anticoagulant cofactor to both activated protein C and tissue factor pathway inhibitor (TFPIα). The TFPIα-cofactor activity of protein S is stimulated by a short isoform of factor V (FV-Short), the two proteins functioning in synergy. Objective Using the synergistic TFPIα-cofactor activity between protein S and FV-Short to develop a functional test for plasma protein S. Patients/Methods TFPIα-mediated inhibition of FXa in the presence of FV-Short, protein S and negatively charged phospholipid vesicles was monitored in time by synthetic substrate S2765. TFPIα, FXa and FV-Short were purified proteins, whereas diluted plasma from protein S deficient patients or controls were used as source for protein S. Results The assay was specific for free protein S demonstrating good correlation to free protein S plasma levels (r = 0.92) with a Y-axis intercept of -5%. Correlation to concentrations of total protein S (free and C4BPß+-bound) was lower (r = 0.88) and the Y-axis intercept was +46%, which is consistent with the specificity for free protein S. The test distinguished protein S-deficient individuals from 6 families with known ProS1 mutations from family members having no mutation. Protein S levels of warfarin-treated protein S deficient cases were lower than protein S in cases treated with warfarin for other causes. Conclusions We describe a new assay measuring the TFPIα-cofactor activity of plasma protein S. The test identifies type I/III protein S deficiencies and will be a useful tool to detect type II protein S deficiency having defective TFPIα-cofactor activity.

Clinical Manifestation and Mutation Spectrum of 53 Unrelated Pedigrees with Protein S Deficiency in China.

Protein S (PS) deficiency is associated with a 10-fold increased risk of venous thromboembolism (VTE), but its diagnosis is quite difficult and complicated. In this study, we identified 53 unrelated pedigrees with PS deficiency in China. Data of their clinical characteristics and laboratory examinations were collected. Genetic analysis of PROS1 including direct sequencing, copy number variant detection and messenger ribonucleic acid analysis was performed in probands and related family members. Of these 53 probands, 52.8% (28/53) experienced multi-site and/or recurrent thrombotic episodes, mainly manifested as deep venous thrombosis and/or pulmonary embolism (82.7%). Additional risk factors of VTE were observed in 39.6% (21/53) probands who exhibited a significantly higher rate of recurrent VTE compared with those not, in which 7 probands were complicated by anti-phospholipid syndrome. Most probands and family members exhibited quantitative PS deficiency with impairment of both activated protein C and tissue factor pathway inhibitor cofactor activities. Note that 87.2% (34/39) PROS1 detectable mutation rate was obtained through comprehensive phenotypic and genetic analysis. A total of 36 PROS1 causative mutations including 16 novel mutations were identified in 48 probands, whereas no PROS1 mutations were detected in the other 5 probands. Three hotspot mutations (Glu67Ala, Arg561Trp and Tyr560*) were identified in the Chinese population for the first time. This article provides a framework for correlating the clinical pathogenesis of PS deficiency to genetic backgrounds in the Chinese population.

Pulmonary thromboendarterectomy in a combined thrombophilia patient.

Chronic thromboembolic pulmonary hypertension (CTEPH) is a potentially correctable cause of secondary pulmonary hypertension. Surgical treatment remains the primary treatment for patients with CTEPH. Pulmonary thromboendarterectomy (PEA) with deep hypothermic circulatory arrest is the standard and recommended surgical technique for the treatment of these patients. The prevalence of CTEPH after an acute pulmonary thromboembolism (PTE) has been found in various studies to be between 0.6 and 8.8%. Mortality rates in elective PEA cases with CTEPH are reported to be between 1.9 and 4.5%. We report on a 50-year-old female patient with combined inherited thrombophilia, including protein C and protein S deficiencies, who was diagnosed with CTEPH and was successfully treated with pulmonary thromboendarterectomy.

Rivaroxaban Causes Missed Diagnosis of Protein S Deficiency but Not of Activated Protein C Resistance (Factor V Leiden).

CONTEXT: - Rivaroxaban causes a false increase in activated protein C resistance (APCR) ratios and protein S activity. OBJECTIVE: - To investigate whether this increase masks a diagnosis of factor V Leiden (FVL) or protein S deficiency in a "real-world" population of patients undergoing rivaroxaban treatment and hypercoagulation testing. DESIGN: - During a 2.5-year period, we compared 4 groups of patients (n = 60): FVL heterozygous (FVL-HET)/taking rivaroxaban, wild-type/taking rivaroxaban, FVL-HET/no rivaroxaban, and normal APCR/no rivaroxaban. Patients taking rivaroxaban were tested for protein S functional activity and free antigen (n = 32). RESULTS: - The FVL-HET patients taking rivaroxaban had lower APCR ratios than wild-type patients ( P < .001). For FVL-HET patients taking rivaroxaban, mean APCR was 1.75 ± 0.12, versus 1.64 ± 0.3 in FVL-HET patients not taking rivaroxaban ( P = .005). Activated protein C resistance in FVL-HET patients fell more than 3 SDs below the cutoff of 2.2 at which the laboratory reflexes FVL DNA testing. No cases of FVL were missed despite rivaroxaban. In contrast, rivaroxaban falsely elevated functional protein S activity, regardless of the presence or absence of FVL ( P < .001). A total of 4 of 32 patients (12.5%) had low free protein S antigen (range, 58%-67%), whereas their functional protein S activity appeared normal (range 75%-130%). Rivaroxaban would have caused a missed diagnosis of all cases of protein S deficiency during the study if testing relied on the protein S activity assay alone. CONCLUSIONS: - Despite rivaroxaban treatment, APCR testing can distinguish FVL-HET from normal patients, rendering indiscriminate FVL DNA testing of all patients on rivaroxaban unnecessary. Free protein S should be tested in patients taking rivaroxaban to exclude hereditary protein S deficiency.

Identification of reference miRNAs in plasma useful for the study of oestrogen-responsive miRNAs associated with acquired Protein S deficiency in pregnancy.

BACKGROUND: Accumulating evidence indicate that circulating microRNAs (miRNAs) are useful independent non-invasive biomarkers, with unique miRNA signatures defined for various pathophysiological conditions. However, there are no established universal housekeeping miRNAs for the normalisation of miRNAs in body fluids. We have previously identified an oestrogen-responsive miRNA, miR-494, in regulating the anticoagulant, Protein S, in HuH-7 liver cells. Moreover, increased thrombotic risk associated with elevated circulating oestrogen levels is frequently observed in pregnant women and oral contraceptive users. In order to identify other oestrogen-responsive miRNAs, including miR-494, that may be indicative of increased thrombotic risk in plasma, we used nanoString analysis to identify robust and stable endogenous reference miRNAs for the study of oestrogen-responsive miRNAs in plasma. RESULTS: We compared the plasma miRNA expression profile of individuals with: (1) Low circulating oestrogens (healthy men and non-pregnant women not taking oral contraceptives), (2) High circulating synthetic oestrogens, (women taking oral contraceptives) and (3) High circulating natural oestrogens (pregnant females >14 weeks gestation). From the nanoString analyses, 11 candidate reference miRNAs which exhibited high counts and not significantly differentially expressed between groups were selected for validation using realtime quantitative polymerase chain reaction (RT-qPCR) and digital droplet PCR (DDPCR) in pooled plasma samples, and the stability of their expression evaluated using NormFinder and BestKeeper algorithms. Four miRNAs (miR-25-5p, miR-188-5p, miR-222-3p and miR-520f) demonstrated detectable stable expression between groups and were further analysed by RT-qPCR in individual plasma samples, where miR-188-5p and miR-222-3p expression were identified as a stable pair of reference genes. The miRNA reference panel consisting of synthetic spike-ins cel-miR-39 and ath-miR159a, and reference miRNAs, miR-188-5p and miR-222-3p was useful in evaluating fold-change of the pregnancy-associated miRNA, miR-141-3p, between groups. CONCLUSION: The miRNA reference panel will be useful for normalising qPCR data comparing miRNA expression between men and women, non-pregnant and pregnant females, and the potential effects of endogenous and synthetic oestrogens on plasma miRNA expression.

Characterization of thrombosis in patients with Proteus syndrome.

Patients with overgrowth and complex vascular malformation syndromes, including Proteus syndrome have an increased risk of thromboembolism. Proteus syndrome is a mosaic, progressive overgrowth disorder involving vasculature, skin, and skeleton, and caused by a somatic activating mutation in AKT1. We conducted a comprehensive review of the medical histories and hematologic evaluations of 57 patients with Proteus syndrome to identify potential risk factors for thrombosis. We found that six of ten patients, who were deceased, died secondary to deep venous thrombosis and/or pulmonary embolism. Of the remaining 47 living patients, six had thromboembolic events that all occurred postoperatively and in an affected limb. Eleven of 21 patients had an abnormal hypercoagulable panel including Factor V Leiden heterozygotes, antithrombin III deficiency, positive lupus anticoagulant, or Protein C or S deficiencies. We observed that eight of 17 patients had an abnormal D-dimer level >0.5 mcg/dl, but deep venous thromboses occurred in only four of those with D-dimer >1.0 mcg/dl. We conclude that the predisposition to thrombosis is likely to be multifaceted with risk factors including vascular malformations, immobility, surgery, additional prothrombotic factors, and possible pathophysiologic effects of the somatic AKT1 mutation on platelet function or the vascular endothelium. The D-dimer test is useful as a screen for thromboembolism, although the screening threshold may need to be adjusted for patients with this disorder. We propose developing a registry to collect D-dimer and outcome data to facilitate adjustment of the D-dimer threshold for Proteus syndrome and related disorders, including PIK3CA-Related Overgrowth Spectrum.

New functional assays to selectively quantify the activated protein C- and tissue factor pathway inhibitor-cofactor activities of protein S in plasma.

Essentials Protein S is a cofactor of activated protein C (APC) and tissue factor pathway inhibitor (TFPI). There are no assays to quantify separate APC and TFPI cofactor activities of protein S in plasma. We developed assays to measure the APC- and TFPI-cofactor activities of protein S in plasma. The assays were sensitive to protein S deficiency, and not affected by the Factor V Leiden mutation. SUMMARY: Background Protein S plays an important role in the down-regulation of coagulation as cofactor for activated protein C (APC) and tissue factor pathway inhibitor (TFPI). Aim To develop functional assays to quantify the APC- and TFPI-cofactor activities of protein S in plasma. Methods APC- and TFPI-cofactor activities of protein S in plasma were measured using calibrated automated thrombography in protein S-depleted plasma supplemented with a small amount of sample plasma either in the presence of anti-TFPI antibodies and APC (APC-cofactor activity) or at excess full-length TFPI without APC (TFPI-cofactor activity). Total and free protein S levels in plasma were measured by ELISAs. Results Average APC-cofactor activities of protein S were 113%, 108% and 89% in plasma from normal individuals (n = 15), FV Leiden heterozygotes (n = 14) and FV Leiden homozygotes (n = 7), respectively, whereas the average APC-cofactor activity of protein S in plasma from heterozygous protein S-deficient individuals (n = 21) was significantly lower (55%). Similar trends were observed for the TFPI-cofactor activity of protein S, with averages of 109%, 115% and 124% in plasma from individuals with normal protein S levels and different FV Leiden genotypes, and 64% in plasma from protein S-deficient patients. APC-cofactor activities of protein S correlated significantly with free and total protein S antigen levels, whereas TFPI-cofactor activities correlated less with protein S antigen levels. Conclusion We have developed functional protein S assays that measure both the APC- and TFPI-cofactor activities of protein S in plasma, which are hardly if at all affected by the FV Leiden mutation.

Birthweight in pregnant women with protein S deficiency treated with low-molecular-weight heparin: a retrospective cohort study.

OBJECTIVE: To determine the risk of small-for-gestational-age (SGA) and intrauterine growth retardation (IUGR) in pregnant women with protein S (PS) deficiency who received low-molecular-weight heparin (LMWH). METHODS: Retrospective cohort study of pregnant women seen from January 2002 to December 2011. The study cohort comprised a total of 328 patients with PS deficiency, who received prophylactic enoxaparin during pregnancy. The control cohort included 11 884 pregnant women without significant past medical history. The risk of SGA and IUGR was calculated as odds ratio. Multivariate regression analysis over the entire reference population was performed determining the risk of both SGA and IUGR by adjusting for maternal age, first delivery, maternal underweight status, pre-eclampsia, other treated thrombophilias or history of recurrent abortion. RESULTS: The SGA rates in the PS deficiency and control cohorts were 10.7% and 8.5%, respectively (p > 0.05). There was no increased risk of SGA (unadjusted OR = 1.28, 95% confidence interval [CI] 0.9-1.83; adjusted OR = 1.35, 95% CI 0.91-2.01). The IUGR rate was 2.7% in pregnant women with PS deficiency versus 4.1% in the control group (p > 0.05). Also, we did not find a significant risk of IUGR (OR = 0.66; 95% CI 0.34-1.28; adjusted OR = 0.843; 95% CI 0.42-1.70). CONCLUSIONS: In women with PS deficiency treated with LMWH, the risk of SGA and IUGR is similar to the one found in healthy pregnant women.

Risk factors associated with provoked pulmonary embolism.

BACKGROUND/AIMS: This study aimed to investigate the risk factors associated with provoked pulmonary embolism (PE). METHODS: This retrospective cohort study included 237 patients with PE. Patients that had transient risk factors at diagnosis were classified as having provoked PE, with the remaining patients being classified as having unprovoked PE. The baseline clinical characteristics and factors associated with coagulation were compared. We evaluated the risk factors associated with provoked PE. RESULTS: Of the 237 PE patients, 73 (30.8%) had provoked PE. The rate of respiratory failure and infection, as well as the disseminated intravascular coagulation score and ratio of right ventricular diameter to left ventricular diameter were significantly higher in patients with provoked PE than in those with unprovoked PE. The protein and activity levels associated with coagulation, including protein C antigen, protein S antigen, protein S activity, anti-thrombin III antigen, and factor VIII, were significantly lower in patients with provoked PE than in those with unprovoked PE. Multivariate analysis showed that infection (odds ratio [OR], 3.2; 95% confidence interval [CI], 1.4 to 7.4) and protein S activity (OR, 0.97; 95% CI, 0.95 to 0.99) were significantly associated with provoked PE. CONCLUSIONS: Protein S activity and presence of infection were important factors associated with provoked PE. We should pay attention to the presence of infection in patients with provoked PE.

Recurrent Hemorrhagic Venous Infarctions Caused by Thrombosis of a Pontine Developmental Venous Anomaly and Protein S Mutation.

A 34-year-old man presented with an acute onset of upbeat nystagmus, slurred speech, and limb and truncal ataxias. The patient had a history of limb ataxia and gait disturbance previously treated as brainstem encephalitis with corticosteroids 3 years previously. Brain magnetic resonance imaging showed pontine developmental venous anomaly (DVA) and hemorrhagic infarction within the drainage territory of the DVA. Three months later, the patient exhibited recurrent limb ataxia, double vision, and numbness of the left side of the body. The brain magnetic resonance imaging revealed recurrent hemorrhagic venous infarction within the same territory of the pontine DVA. Laboratory tests disclosed a hypercoagulable state owing to a decrease of protein S activity despite the normal antigen level. Genetic testing indicated that the patient was a homozygous carrier of protein S Tokushima. The patient's severe disability remained unchanged in spite of treatment with anticoagulation therapy using warfarin. We propose that further research on hereditary coagulopathy be carried out in patients with recurrent episodes of DVA-related infarction.

Influenza-associated thrombotic microangiopathy with unbalanced von Willebrand factor and a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 levels in a heterozygous protein S-deficient boy.

Influenza infections often cause pneumonia, but there is limited information on thrombotic microangiopathy (TMA) in these circumstances. We report the case of an 11-year-old boy who developed TMA during the acute phase of H1N1 influenza. Plasma von Willebrand factor (VWF) was elevated, whereas a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) activity was mildly reduced in the absence of ADAMTS13-neutralizing autoantibody, resulting in low ratio of ADAMTS13 to VWF. The patient was treated intensively, including plasma exchange, and he recovered from the TMA. He developed pulmonary embolism (PE), however, after removal of the central venous catheter. The findings suggested that influenza-associated cytokines enhanced the release of unusually large VWF multimers from vascular endothelial cells and promoted the formation of platelet thrombi and TMA. Subsequent analysis further indicated the presence of familial protein S deficiency, and it seemed likely that the PE was more related to this heterozygous protein S defect.

Thrombin generation and cell-dependent hypercoagulability in sickle cell disease.

Essentials Sickle cell disease is increasingly being recognized as a chronic hypercoagulable state. Thrombin generation is elevated in the whole blood, but not the plasma of sickle cell patients. Whole blood thrombin generation inversely correlates to erythrocyte phosphatidylserine exposure. Acquired protein S deficiency is likely explained by binding of protein S to sickle red cells. Click to hear Dr Hillery discuss coagulation and vascular pathologies in mouse models of sickle cell disease. SUMMARY: Introduction Sickle cell disease (SCD) is a hypercoagulable state with chronic activation of coagulation and an increased incidence of thromboembolic events. However, although plasma pre-thrombotic markers such as thrombin-anithrombin complexes and D-dimer are elevated, there is no consensus on whether global assays of thrombin generation in plasma are abnormal in patients with SCD. Based on our recent observation that normal red blood cells (RBCs) contribute to thrombin generation in whole blood, we hypothesized that the cellular components in blood (notably phosphatidylserine-expressing erythrocytes) contribute to enhanced thrombin generation in SCD. Methods Whole blood and plasma thrombin generation assays were performed on blood samples from 25 SCD patients in a non-crisis 'steady state' and 25 healthy race-matched controls. Results Whole blood thrombin generation was significantly elevated in SCD, whereas plasma thrombin generation was paradoxically reduced compared with controls. Surprisingly, whole blood and plasma thrombin generation were both negatively correlated with phosphatidylserine exposure on RBCs. Plasma thrombin generation in the presence of exogenous activated protein C or soluble thrombomodulin revealed deficiencies in the protein C/S anticoagulant pathway in SCD. These global changes were associated with significantly lower plasma protein S activity in SCD that correlated inversely with RBC phosphatidylserine exposure. Conclusion Increased RBC phosphatidylserine exposure in SCD is associated with acquired protein S deficiency. In addition, these data suggest a cellular contribution to thrombin generation in SCD (other than RBC phosphatidylserine exposure) that explains the elevated thrombin generation in whole blood.

Protein S testing in patients with protein S deficiency, factor V Leiden, and rivaroxaban by North American Specialized Coagulation Laboratories.

In 2010-2012, the North American Specialized Coagulation Laboratory Association (NASCOLA) distributed 12 proficiency testing challenges to evaluate laboratory testing for protein S (PS). Results were analysed to assess the performance of PS activity, PS free antigen, and PS total antigen testing. Statistical analysis was performed on the numeric results and qualitative classification submitted for each method. There were 2,106 total results: 716 results from PS activity assays, 833 results from PS free antigen assays, and 557 results from PS total antigen assays. The three assay types performed well in the classification of five normal samples and nine abnormal samples, although certain PS activity methods were more likely to classify normal samples as abnormal and one PS total antigen assay was more likely to classify abnormal samples as normal. PS activity methods were affected by interfering substances such as heterozygous or homozygous factor V Leiden mutation (underestimation) and the anticoagulant drug rivaroxaban (overestimation). In conclusion, NASCOLA laboratories using a variety of PS assays performed well in the classification of clearly normal and abnormal samples. Laboratories performing PS activity assays should be aware of potential interferences in samples positive for FV Leiden or containing certain anticoagulant medications.