The influence of dead space in blood sampling needle on FVIII level and pharmacokinetic profiles in children with hemophilia.

OBJECTIVE: To investigate the influence of the dead space in disposable blood sampling needle on activated partial thromboplastin time (APTT), FVIII level and pharmacokinetic (PK) profiles in children with hemophilia. METHODS: Children (<18 years) with severe hemophilia A were enrolled. After three days' washout-period, blood samples were collected at pre-dose, 1 h, 3 h, 9 h, 24 h and 48 h post-infusion. At each timepoint, two 2 mL vacuum tubes with 3.2% trisodium citrate were used. The first tube was signed as 'non-standard' (NS) and the second tube was signed as 'standard' (S). FVIII activities were evaluated by one-stage assay. WAPPS-Hemo was used to generate PK profiles like half-life time (t1/2), clearance (CL), trough level and time to 1, 2 and 5IU/dL after a dose of 50 ± 10IU/dL. The FVIII activities at 9 h and 24 h post-infusion were put into WAPPS and thus brought four combinations by true or biased FVIII level that used. RESULT: Compared with standard-collected blood samples, prolonged APTT results (P-values < 0.01) and decreased FVIII activity (P-values < 0.05) were revealed in those non-standard blood samples. The corresponding bias was in positive relation to both APTT-S (r = 0.44, P < 0.0001) and FVIII-S level(r = 0.68, P < 0.001). The FVIII bias percentage got larger as FVIII-S level reduced (r = -0.24, P < 0.01). During the four combinations of FVIII activity at 9 h and 24 h, statistically longer t1/2, lower CL and longer time to 1, 2 or 5IU/dL were observed in 9H-S&24H-S group and 9H-NS&24H-S group. CONCLUSION: While using vacuum tubes for clotting indicators and PK profiles, the dead space of blood sampling needle should be eliminated in advance.

A single-institution retrospective study of causes of prolonged prothrombin time and activated partial thromboplastin time in the outpatient setting.

INTRODUCTION: An algorithmic approach, termed the prolonged clot time profile (PROCT), consisting of initial screening with prothrombin time (PT) and activated partial thromboplastin time (aPTT), reflexive mixing studies if indicated, and follow-up assays depending on initial testing results, offers an efficient approach to delineate the etiology of a prolonged PT/aPTT. Herein, we present the outcomes of the PROCT in the outpatient setting. METHODS: In this retrospective study, we reviewed medical records of consecutive outpatients who had prolonged PT and/or aPTT noted in the routine coagulation laboratory and who had PROCT ordered in our institutional Special Coagulation Laboratory between 2010 and 2017. RESULTS: One hundred and six patients, median age 55 years (IQR 30-67), met our study criteria. Twenty-nine patients had normal PT/aPTT, while 77 had persistent abnormalities and underwent reflexive testing. A prolonged PT, aPTT, or PT and aPTT was noted in 27 (35%), 27 (35%), and 23 (30%) respectively. Forty-nine (64%) had an acquired condition, 17 (22%) had a congenital condition, 7 (9%) had unclear etiology, and 4 (5%) were the result of laboratory artifact. The most common known cause of an isolated prolonged PT in our study was vitamin K deficiency in 8 (10%), the most common cause of an isolated prolonged aPTT was lupus anticoagulant in 4 (5%), and the most common cause of prolonged PT and aPTT was liver disease in 11 (14%). CONCLUSION: Prolonged PT/aPTT have a wide range of causes, including artifactual prolongation or abnormalities in secondary hemostasis due to both inherited and acquired conditions.

Reflex factor coagulation testing in patients with an unexplained prolonged aPTT: An institutional retrospective review.

BACKGROUND: We aim to determine the clinical utility of reflex coagulation investigations (RCI) for prolonged lupus insensitive activated partial thromboplastin time (aPTT) at our institution. METHODS: We retrospectively reviewed all potential RCI (lupus insensitive aPTT of ≥32s) from April 2014 to June 2019. Our diagnostic algorithm requires completion of RCI only if samples had no interfering medications to explain a prolonged aPTT and were either from a preoperative sample or from a patient presenting with unexplained bleeding. Appropriate RCI samples undergo further investigations with one-stage factor activity testing for factors 8(FVIII), 9(FIX), and 11(FXI) reflexively. Data were obtained through electronic medical records to capture clinical characteristics, laboratory findings, prophylactic hemostatic replacement, and bleeding outcomes. RESULTS: Three thousand and three hundreds seventeen samples from 2940 distinct patients were considered as potential RCI during the study period. 263/3317 (8%) samples had RCI completed. Of those, 55/263 (21%) had abnormal factor testing, with the majority from preoperative setting (43/55; 78%). 5/43 (12%) patients were referred to hematology for preoperative evaluation. 5/43 patients received preoperative hemostatic support. A total of 5 patients (5/43) developed postop bleeding. Six patients (6/55) had RCI for unexplained bleeding, and five patients (83%) had a newly identified clinically significant bleeding disorder. CONCLUSION: Reflex coagulation investigations benefited patients presenting with unexplained bleeding as this expedited the diagnosis and management of clinically significant bleeding disorders. RCI for preoperative evaluation infrequently led to additional hemostatic support/referral to hematology. The lack of additional workup for an abnormal factor activity level suggests laboratory alert fatigue as a potential contributory factor.

Identification of the factor XII contact activation site enables sensitive coagulation diagnostics.

Contact activation refers to the process of surface-induced activation of factor XII (FXII), which initiates blood coagulation and is captured by the activated partial thromboplastin time (aPTT) assay. Here, we show the mechanism and diagnostic implications of FXII contact activation. Screening of recombinant FXII mutants identified a continuous stretch of residues Gln317-Ser339 that was essential for FXII surface binding and activation, thrombin generation and coagulation. Peptides spanning these 23 residues competed with surface-induced FXII activation. Although FXII mutants lacking residues Gln317-Ser339 were susceptible to activation by plasmin and plasma kallikrein, they were ineffective in supporting arterial and venous thrombus formation in mice. Antibodies raised against the Gln317-Ser339 region induced FXII activation and triggered controllable contact activation in solution leading to thrombin generation by the intrinsic pathway of coagulation. The antibody-activated aPTT allows for standardization of particulate aPTT reagents and for sensitive monitoring of coagulation factors VIII, IX, XI.

Pediatric Thromboelastograph 6s and Laboratory Coagulation Reference Values.

CONTEXT.­: Specific reference intervals (RIs) facilitate accurate interpretation of results. Coagulation assay results may vary by demographics and also between reagents and analyzers used. Current Thromboelastograph 6s (TEG 6s) Hemostasis Analyzer RIs were generated from adult samples. OBJECTIVE.­: To generate reagent analyzer-specific pediatric RIs for TEG 6s and coagulation parameters. DESIGN.­: A prospective, observational, single-center study of healthy children undergoing general anesthesia (January 3, 2017 to January 3, 2019). Venous blood samples were obtained for TEG 6s (Kaolin, Kaolin-Heparinase, Rapid and Functional Fibrinogen assays) and coagulation parameters (activated partial thromboplastin time, prothrombin time, thrombin clotting time, Echis time, antithrombin activity, and fibrinogen concentration using Instrumentation Laboratory ACL-TOP analyzers). Differences between activated partial thromboplastin time and prothrombin time reagents were investigated using mixed-effects regression, comparing maximum coefficients-of-variation with assay-specific allowable variation. RIs (lower/upper limits 2.5th of 97.5th percentiles) were generated using the following 2 methods: within discrete age-groups (neonates [<1 month], infants [1 month-1 year], young children [1-5 years], older children [6-10 years], and adolescents [11-16 years]), and modeled as functions of age and/or sex using quantile regression, including significant fractional polynomial and interaction terms. RESULTS.­: Variation between prothrombin time and activated partial thromboplastin time assays using different reagents was clinically significant. Reagent-analyzer specific pediatric RIs were generated using data from 254 children. Discrete and model-based RIs varied by age for all coagulation parameters and TEG 6s variables in all assays. CONCLUSIONS.­: We report reagent-analyzer specific pediatric RIs for TEG 6s and coagulation parameters. Observed variation reinforces recommendations for laboratory-specific RIs. These findings improve accuracy of interpretation of clinical results, provide a foundation for comparison and validation of tests in pathology, and illustrate feasibility and advantages of model-based RI approaches.

Clinical utility of activated partial thromboplastin time clot waveform analysis and thrombin generation test in the evaluation of bleeding phenotype in Hemophilia A.

CONTEXT: Hemophilia A is classified as mild, moderate, and severe based on Factor VIII levels (FVIII). Clot-based assays only detect initiation of thrombin generation, hence FVIII levels may not accurately predict the bleeding risk in all hemophilia patients. The entire process of thrombin generation as measured by global hemostasis tests like activated partial thromboplastin time clot waveform analysis (APTT CWA) and thrombin generation test (TGT) may reflect the actual bleeding phenotype. AIMS: To assess the utility of TGT and CWA as a screening tool to identify bleeders and to evaluate the bleeding phenotype in Hemophilia A. SETTINGS AND DESIGN: Prospective, observational study of 147 consecutive patients referred for coagulation workup. SUBJECTS AND METHODS: Bleeding assessment tool was used to identify bleeders. Patients were classified as severe and nonsevere bleeders based on clinical criteria. TGT was performed by calibrated automated thrombogram, CWA by photo-optical coagulometer and factor levels by one stage clot-based assays. STATISTICAL ANALYSIS USED: The Kruskal-Wallis test with post-hoc analysis was done to examine the difference in CWA/TGT parameters amongst hemophilia classified by FVIII levels. Receiver operating characteristic (ROC) analysis was performed to estimate the diagnostic accuracy of CWA and TGT in discriminating between clinically severe vs nonsevere bleeders. RESULTS: Using ROC derived cut-offs of min1, min2 and peak height of thrombin (PH), the sensitivity (min1:91.67%, min2:91.67%, PH: 97.22%, FVIII: 86.11%) and specificity (min1:100%, min2:100%, PH: 90.91%, FVIII: 90.91%) of CWA/TGT was superior to FVIII to distinguish between clinically severe vs nonsevere bleeders. Phenotypic heterogeneity of bleeding severity was identified in our study population. Clinical severity correlated with CWA/TGT parameters instead of FVIII levels. CONCLUSIONS: CWA and TGT are more effective tools than conventional factor assays to identify clinically severe bleeders and tailor prophylaxis as per bleeding phenotype.

Overall hemostasis potential and aPTT-clot waveform analysis as powerful laboratory diagnostic tools for identification of hemophilia A patients with unexpected bleeding phenotype.

INTRODUCTION: Traditionally used laboratory methods do not always accurately reflect bleeding severity in hemophilia A (HA) patients. The ability of three global assays for identifying patients with unexpected bleeding phenotype was investigated. METHODS: Overall hemostasis potential (OHP), aPTT-clot waveform analysis (aPTT-CWA), endogenous thrombin potential (ETP), FVIII activities, and prothrombin fragment 1 + 2 concentrations were measured in 62 HA patients (30 severe and 32 non-severe) and 27 male controls. Bleeding phenotype was determined using our proposed scoring system including age at first joint bleed, number of target joints, and number of joint/muscle bleeds per year. Bleeding score ≤ 4 defined patients with mild bleeding phenotype (N = 27); score ≥ 5 defined severe bleeding phenotype (N = 35). RESULTS: The receiver operating characteristic analysis performed for distinguishing patients with severe and mild bleeding phenotype yielded following values of area under the curve: 0.910 (FVIII); 0.891 (aPTT-CWA parameter DELTA); 0.769 (OHP); and 0.634 (ETP). Unexpected bleeding phenotype was identified in 11/62 HA patients: 8/32 (25%) non-severe HA patients had severe, while 3/30 (10%) severe HA patients had mild bleeding phenotype, and global assays enabled the identification of all these patients. OHP and DELTA were revealed as the most reliable parameters for bleeding phenotype determination (10/11 and 9/11 unexpected results, respectively). CONCLUSION: This study emphasizes OHP and aPTT-CWA as a powerful laboratory diagnostic tool in identifying HA patients with unexpected bleeding presentations, with the best results achieved by combining both assays. Global assays should not completely replace FVIII activity measurement but should be a part of the HA diagnostic algorithm.

Effectiveness of a Calculation-Free Weight-Based Unfractionated Heparin Nomogram With Anti-Xa Level Monitoring Compared With Activated Partial Thromboplastin Time.

BACKGROUND: Accurate monitoring of intravenous unfractionated heparin (UFH) is essential to mitigate the risk of adverse drug events associated with dosing errors. Although recent data support anti-factor Xa (anti-Xa) monitoring preferentially over activated partial thromboplastin time (aPTT) to improve time to therapeutic anticoagulation, the utility of incorporating anti-Xa monitoring with a calculation-free weight-based UFH nomogram has not been formally evaluated. OBJECTIVE: The primary objective of this study was to evaluate the time to therapeutic anticoagulation of a calculation-free weight-based UFH nomogram integrated with anti-Xa monitoring versus a historical control of aPTT monitoring utilizing manual dose calculations. METHODS: This was a retrospective analysis of patients with anti-Xa monitoring and a novel calculation-free weight-based UFH nomogram compared with a historical control with aPTT monitoring and manual calculations. RESULTS: A total of 103 patients in the aPTT cohort and 100 patients in the anti-Xa cohort were analyzed. The anti-Xa cohort achieved goal therapeutic target 3.8 hours sooner than the aPTT cohort (P = 0.03). Patients with anti-Xa monitoring required 1 fewer adjustment per 2.5 patient-days of UFH with the venous thromboembolism nomogram (P = 0.02). Patients in the aPTT cohort required more infusion interruptions because of supratherapeutic values (P = 0.007) and boluses because of subtherapeutic values (P = 0.044). There were no differences in rates of thromboembolism, major bleeding, or clinically relevant nonmajor bleeding between the cohorts. CONCLUSION AND RELEVANCE: This study demonstrated that anti-Xa UFH monitoring integrated with a calculation-free nomogram results in faster time to therapeutic anticoagulation and fewer dose adjustments compared with aPTT monitoring with manual calculations.

Unexpected, isolated activated partial thromboplastin time prolongation: A practical mini-review.

A common inquiry in coagulation laboratories is how to interpret an unexpected, isolated prolonged activated partial thromboplastin time (APTT). In this context, isolated means together with a normal prothrombin time (PT) and/or normal international normalized ratio (INR). This finding may lead to contact with laboratory doctors for further advice on a diagnostic strategy. Occasionally, the need for a diagnostic algorithm can be subacute, where surgery has to be postponed until an explanation for the isolated, prolonged APTT has been established. Activated partial thromboplastin time as a coagulation test was developed to monitor patients with hemophilia. Different APTT reagents display considerable differences in their sensitivity to deficiencies of coagulation factors. An isolated, prolonged APTT is seen in (a) individuals/patients with lupus anticoagulants, (b) patients in treatment with anticoagulants, mainly heparin, and (c) patients with deficiencies of specific coagulation factors. In this tutorial review, we summarize what may cause an isolated prolonged APTT and we present a simple diagnostic algorithm to differentiate between lupus anticoagulants (common) and factor deficiencies (rare). The identification of an isolated prolonged APTT as well as the underlying cause can be of the utmost importance in ensuring the correct therapeutic follow-up.

Emergency medicine misconceptions: Utility of routine coagulation panels in the emergency department setting.

BACKGROUND: Coagulation panels are ordered for a variety of conditions in the emergency department (ED). OBJECTIVE: This narrative review evaluates specific conditions for which a coagulation panel is commonly ordered but has limited utility in medical decision-making. DISCUSSION: Coagulation panels consist of partial thromboplastin time (PTT) or activated partial thromboplastin time (aPTT), prothrombin time (PT), and international normalized ratio (INR). These tests evaluate the coagulation pathway which leads to formation of a fibrin clot. The coagulation panel can monitor warfarin and heparin therapy, evaluate for vitamin K deficiency, evaluate for malnutrition or severe systemic disease, and assess hemostatic function in the setting of bleeding. The utility of coagulation testing in chest pain evaluation, routine perioperative assessment, prior to initiation of anticoagulation, and as screening for admitted patients is low, with little to no change in patient management based on results of these panels. Coagulation testing should be considered in systemically ill patients, those with a prior history of bleeding or family history of bleeding, patients on anticoagulation, or patients with active hemorrhage and signs of bleeding. Thromboelastography and rotational thromboelastometry offer more reliable measures of coagulation function. CONCLUSIONS: Little utility for coagulation assessment is present for the evaluation of chest pain, routine perioperative assessment, initiation of anticoagulation, and screening for admitted patients. However, coagulation panel assessment should be considered in patients with hemorrhage, patients on anticoagulation, and personal history or family history of bleeding.

Clinical utility and impact of the use of the chromogenic vs one-stage factor activity assays in haemophilia A and B.

Treatment of haemophilia A/B patients comprises factor VIII (FVIII) or factor IX (FIX) concentrate replacement therapy, respectively. FVIII and FIX activity levels can be measured in clinical laboratories using one-stage activated partial thromboplastin time (aPTT)-based clotting or two-stage chromogenic factor activity assays. We discuss strengths and limitations of these assays, providing examples of clinical scenarios to highlight some of the challenges associated with their current use for diagnostic and monitoring purposes. Substantial inter-laboratory variability has been reported for one-stage assays when measuring the activity of factor replacement products due to the wide range of currently available aPTT reagents, calibration standards, factor-deficient plasmas, assay conditions and instruments. Chromogenic activity assays may avoid some limitations associated with one-stage assays, but their regulatory status, perceived higher cost, and lack of laboratory expertise may influence their use. Haemophilia management guidelines recommend the differential application of one or both assays for initial diagnosis and disease severity characterisation, post-infusion monitoring and replacement factor potency labelling. Efficient communication between clinical and laboratory staff is crucial to ensure application of the most appropriate assay to each clinical situation, correct interpretation of assay results and, ultimately, accurate diagnosis and optimal and safe treatment of haemophilia A or B patients.

[Clinical laboratory criteria and its utility as predictive of diagnosis of the cardiopulmonary syndrome by hantavirus]. / Criterios de laboratorio clínico y su utilidad como predictores del diagnóstico de síndrome cardiopulmonar por hantavirus.

BACKGROUND: The hantavirus infection is an emerging zoonotic disease, endemic in Chile, generating the hantavirus cardiopulmonary syndrome (HCPS), characterized by cardiopulmonary dysfunction with rapidly progressive respiratory failure and high lethality. For an early clinical orientation of HCPS, due to its non-specificity in symptoms and to help the differential diagnosis, some laboratory parameter that may be useful have been studied. AIM: To identify laboratory criteria as predictive factors of HCPS in patients with suspected hantavirus infection. METHODOLOGY: Retrospective cohort study of 71 patients admitted to the Hospital Guillermo Grant Benavente Emergency. We determined discriminative capacity of laboratory's parameters at the time of admission: platelets recount, hematocrit, inmunoblasts, activated partial thromboplastin time (aPTT) and aspartate aminotransferase (AST/GOT). RESULTS: Were found significant differences in all parameters studied between confirmed patients (22) with respect to unconfirmed (49). Hematocrit, inmunoblasts, AST/GOT and aPTT had a OR > 1 and platelets count had a OR < 1. The best combination for predict HCPS was hematocrit, platelets count and AST/GOT with 90,01% sensibility and 81,63% specificity. CONCLUSION: The five parameters studied are good predictors of HCS in suspicious patients and they would may be useful in low complexity hospitals for quick transfer a center with critical care units.

Application of thrombelastography in primary total knee and total hip replacement: a prospective 87 patients study.

: Thrombelastography (TEG) parameters and prothrombin time (PT), activated partial thromboplastin time (APTT) are compared and analysed. According to change of TEG parameters and assessment of haemostatic state of each patient, we try to explore the feasibility of individualized anticoagulant therapies. 87 people with hip or knee diseases awaiting arthroplasty were recruited. Haemoglobin levels and TEG parameters including R, K, α-angle, maximum amplitude, coagulation index were assessed in perioperative period. PT and APTT were assessed preoperatively. For 65 patients with normal TEG parameters, PT and APTT, we use tranexamic acid (TXA) to reduce blood loss during operation. As hypercoagulability group, 12 patients awaiting unilateral total knee arthroplasty with hypercoagulable state assessed by TEG parameters or risks for venous thromboembolism received daily 10-mg rivaroxaban until 24 h preoperatively and did not receive TXA during operation. All patients received intravenous administration of argatroban after 8 h postoperatively until day 3 and oral administration of rivaroxaban (10 mg) subsequently to prevent deep vein thrombosis or/and pulmonary embolism until 35 days postoperatively. TEG parameters have significant relationships with fibrinogen, platelet and APTT. The number of patients with abnormal haemostatic state assessed by TEG parameters is higher than that assessed by PT, APTT. TEG show hypercoagulability develops throughout perioperative period. There was no significant difference in haemoglobin concentration between hypercoagulability group and normal group in patients receiving unilateral total knee arthroplasty. TEG have higher sensitivity of perioperative abnormal haemostatic state than PT, APTT in primary arthroplasty. For patients with hypercoagulability, individualized anticoagulant therapies such as preoperative administration of rivaroxaban and not using TXA in operation is safe and effective.

Criterios de laboratorio clínico y su utilidad como predictores del diagnóstico de síndrome cardiopulmonar por hantavirus / Clinical laboratory criteria and its utility as predictive of diagnosis of the cardiopulmonary syndrome by hantavirus

Resumen Introducción: La infección por hantavirus es una zoonosis emergente, endémica en Chile, generando el síndrome cardiopulmonar por hantavirus (SCPH), caracterizado por disfunción cardiopulmonar con falla respiratoria rápidamente progresiva y altamente letal. Para una orientación clínica precoz del SCPH, debido a su poca especificidad en síntomas y ayudar al diagnóstico diferencial, se han estudiado algunos parámetros de laboratorio que puedan ser de utilidad. Objetivo: Identificar criterios del laboratorio como factores predictores del diagnóstico de SCPH en pacientes con sospecha de enfermedad por hantavirus. Metodología. Estudio de cohorte retrospectiva de 71 pacientes que ingresaron a Urgencia del Hospital Guillermo Grant Benavente. Se determinó la capacidad discriminativa de parámetros de laboratorio al momento de ingreso: recuento de plaquetas, hematocrito, inmunoblastos, TTPa y GOT. Resultados: Se encontraron diferencias significativas en los parámetros estudiados entre pacientes confirmados (n: 22) con respecto a los no confirmados (n: 49). Hematocrito, inmunoblastos, GOT y TTPa tuvieron un OR > 1 y las plaquetas un OR < 1. La mejor combinación para predecir SCPH fue hematocrito, plaquetas y GOT con sensibilidad 90,9% y especificidad 81,6%. Conclusión: Los cinco parámetros estudiados son buenos predictores de SCPH en pacientes con sospecha del mismo y podrían ser útiles en hospitales de baja complejidad para rápido traslado a centro que cuente con unidad de pacientes crítico.

Background. The hantavirus infection is an emerging zoonotic disease, endemic in Chile, generating the hantavirus cardiopulmonary syndrome (HCPS), characterized by cardiopulmonary dysfunction with rapidly progressive respiratory failure and high lethality. For an early clinical orientation of HCPS, due to its non-specificity in symptoms and to help the differential diagnosis, some laboratory parameter that may be useful have been studied. Aim: To identify laboratory criteria as predictive factors of HCPS in patients with suspected hantavirus infection. Methodology: Retrospective cohort study of 71 patients admitted to the Hospital Guillermo Grant Benavente Emergency. We determined discriminative capacity of laboratory's parameters at the time of admission: platelets recount, hematocrit, inmunoblasts, activated partial thromboplastin time (aPTT) and aspartate aminotransferase (AST/GOT). Results: Were found significant differences in all parameters studied between confirmed patients (22) with respect to unconfirmed (49). Hematocrit, inmunoblasts, AST/GOT and aPTT had a OR > 1 and platelets count had a OR < 1. The best combination for predict HCPS was hematocrit, platelets count and AST/GOT with 90,01% sensibility and 81,63% specificity. Conclusion: The five parameters studied are good predictors of HCS in suspicious patients and they would may be useful in low complexity hospitals for quick transfer a center with critical care units.

Comparison of clot-based and chromogenic assay for the determination of protein c activity.

: Activated protein C inactivates factor Va and VIIIa. Deficiency of this natural anticoagulant may result in recurrent venous thrombosis. Performance characteristics of clot-based and chromogenic protein C activity assays are different. The clot-based assay has limitations because of interference with coagulation inhibitors resulting in spuriously increased protein C levels or underestimation because of elevated levels of factor VIII and Factor V-Leiden mutation. The chromogenic assay is not influenced by such interferences but only detects functional defects of protein C that involve the active site rendering it insensitive to rare mutations. To compare two methods, we conducted a retrospective study from January 2015 to June 2017. Our results showed a good correlation between clot-based and chromogenic assay (R = 0.94 and r = 0.88). The study of agreement between the two methods by the Bland-Altman method showed that chromogenic method on an average measures 7.8% more protein C than that of clot-based. The results also showed that the bias between the two methods is significant. The positive trend noted was contributed by the values of less than 20% of protein C. Both clot-based and chromogenic assays had high sensitivity; however, the chromogenic assay showed better specificity (97%) as compared with the clot-based assay (93%). In conclusion, we recommend the chromogenic method as the assay of choice, which is also recommended by the College of American Pathologist Consensus Study over activated partial thromboplastin time-based assay. We have shown here that despite a good correlation between the two techniques, there is a difference as highlighted by the difference plots.

Laboratory assay measurement of modified clotting factor concentrates: a review of the literature and recommendations for practice.

Over the past several years, novel modified clotting factor concentrates (CFCs) have been introduced into practice and are now widely prescribed in the countries where they are licensed. These products allow for less frequent infusions of CFC, thereby providing improved convenience and/or higher trough levels. They have been extensively studied for prophylaxis, episodic treatment of bleeding and for surgical prophylaxis. One issue that has emerged regarding the clinical application of these products revolves around the measurement of infused CFC in the clinical coagulation laboratory. Recent studies have demonstrated significant problems with the measurement of correct FVIII/IX levels following infusion of novel CF VIII/IX concentrates. The source of this problem appears to be related to the tremendous variability of the APTT reagents that are used in the one-stage clotting assay, the most commonly used assay for determining factor levels. More specifically, the issue is related to the type of activator used in the reagents. Depending on the combination of the CFC and the APTT activator, the observed results may be either under- or overestimated to degrees that would be clinically relevant. Recommendations based on a review of published information regarding the potential for incorrect measurements of factor VIII/IX levels following infusion of recently developed, novel factor VIII/IX CFCs are presented for the clinician to use in clinical practice.

Evolution of haemostatic parameters and risk of bleeding during treatment with cefazolin.

In 2017, five cases of severe haemorrhages during treatment with cefazolin occurred in France. The aim of this study was to assess the risk of haemorrhage related to treatment with cefazolin by evaluating haemostatic parameters and bleeding events. A retrospective study was conducted from January 2016 to December 2017. Two populations were analysed: (i) overall population, which included all patients treated with cefazolin during this period and (ii) coagulation study population, which included all patients treated with cefazolin with available coagulation parameters (activated partial thromboplastin time (aPTT) and international normalised ratio (INR) at baseline and at the end of treatment or EoT). Values of either aPTT or INR at baseline and at EoT were compared. Cases of severe haemorrhages were reported and correlated with values of aPTT and INR. Overall, 132 patients received cefazolin and 59/132 (45%) were included in the coagulation study group. A significant increase of median aPTT was observed from baseline to EoT (39.5 and 44.3 sec; p = 0.004, respectively). Overall, severe haemorrhage occurred in 7/132 (5%) patients. Coagulation parameters were available in three of them, and no correlation was observed between bleeding events and aPTT increase. This study showed that bleeding is probably more frequent than ever reported before during cefazolin treatment. The significant increase of aPTT observed during cefazolin treatment was not correlated with risk of haemorrhage. Further studies are needed to explore the possible physio-pathological pathways behind the modification of haemostatic parameters and risk of haemorrhage.

Performance of a recombinant fusion protein linking coagulation factor IX with recombinant albumin in one-stage clotting assays.

Essentials Performance of the one-stage clotting (OSC) assay varies with the clotting activator used. Recombinant FIX-albumin fusion protein (rIX-FP) was reliably monitored with most OSC reagents. rIX-FP shows comparable reagent-dependent variability to other rFIX products in the OSC assay. Actin® FS and kaolin-based reagents underestimated rIX-FP activity by around 50% in the OSC assay. SUMMARY: Background Measuring factor IX activity (FIX:C) with one-stage clotting (OSC) assays, based on the activated partial thromboplastin time (APTT), is the current mainstay of diagnostic techniques for hemophilia B. Assessing the performance of new recombinant FIX (rFIX) products in OSC assays is essential, as APTT reagents from different manufacturers yield different potency estimates for rFIX. Objectives To evaluate the extent to which choice of reagent composition influences rFIX potency measurements of recombinant FIX-albumin fusion protein (rIX-FP, IDELVION) activity in OSC assays. Methods rIX-FP was added to FIX-deficient plasma, and FIX:C was assessed centrally and locally in a multicenter international field study with a variety of commercial OSC APTT reagents. Paired sample analysis of clinical samples was performed to compare values of FIX:C from local and central laboratories. In-house bioanalytical investigations with spiked samples were conducted to compare the APTT-reagent dependent variability of rIX-FP with unmodified rFIX and rFIX Fc fusion protein (rFIXFc). Results Central and local assessments of FIX:C from 10 countries and 21 participating centers showed comparable results to those from the central laboratory across the majority of 18 different APTT reagents from both clinical and spiked samples. There was a consistent underestimation of rIX-FP activity of ≈ 50% with OSC assays using Actin FS or kaolin-based APTT reagents. In the bioanalytical study, rIX-FP showed comparable variability in OSC assays to unmodified rFIX and rFIXFc. Conclusions rIX-FP activity can be accurately measured by the use of OSC assays with the majority of commercial reagents. Actin FS or kaolin-based reagents will probably lead to a 50% underestimation of activity.

Reliability of the portable coagulometer qLabs to accurately measure the activated thromboplastin time and international normalized ratio: a prospective study in critically ill patients.

: The current prospective study was aimed at investigating whether a portable coagulometer (qLabs) can be used to reliably monitor activated thromboplastin time (aPTT) and international normalized ratio (INR) in critically ill patients, as compared with standard central laboratory measurement. Both precision and accuracy of INR and aPTT measured by qLabs were assessed in this observational study by finger prick group (N = 30 patients) and blood droplet group from central venous catheter drawn (N = 60). For accuracy, clinical agreement percentage was ±0.3 for INR and ±10 s for aPTT. Precision of INR measurement in qLabs showed excellent intraclass correlation coefficient (ICC > 90%). Precision of aPTT measurement in qLabs was less acceptable for both finger prick [ICC: 0.70; Bland-Altman plot: 2.2 s (-19.8, 24.2)] and blood droplet [ICC: 0.50; Bland-Altman plot: 0.4 s (-70.9, 71.8)] groups. Accuracy of qLabs was acceptable for INR assessment (clinical agreement 90 and 81%, for finger prick and blood droplet groups, respectively), but not for aPTT (clinical agreement 55 and 68%, respectively). Accuracy of finger prick and blood droplet measurements in qLabs was better for INR and aPTT values near-to-normal (1.2 and 37 s, respectively). INR values from qLabs were consistent with the 'gold standard'. qLabs measurement is only reliable for aPTT values near-to-normal.