Are tube fill volumes below 90% a rejection criterion for all coagulation tests?

BACKGROUND: Rejected samples lead to prolonged turnaround time and delayed diagnosis and treatment of patients. This study was conducted to determine minimum acceptable sample volume in Sarstedt brand coagulation tubes to reduce high sample rejection rate. METHODS: Blood samples were drawn from 20 participants (10 healthy volunteers and 10 patients receiving oral anticoagulant) into coagulation tubes. Six samples were taken from each participant, with tube fill volumes of 100%, 90%, 80%, 70%, 60%, and 50%. Prothrombin time (PT), active partial thromboplastin time (aPTT), and fibrinogen tests were analyzed. RESULTS: According to quality performance specifications, the tube fill volume must be at least 70% for PT and aPTT and 50% for fibrinogen. There was no statistical difference in samples from healthy volunteers for PT, aPTT, and fibrinogen tests when the minimum tube fill volume was at least 80%, 90%, and 50%, respectively. These percentages were 50%, 70%, and 60%, respectively, in patients receiving oral anticoagulant. CONCLUSIONS: Sarstedt tubes meet quality standard specifications at a 70% fill rate for PT and aPTT and a 50% fill rate for fibrinogen. Comprehensive studies with larger populations are needed to accept these values as sample acceptance criteria for the laboratory.

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.

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.

Standardization of Prothrombin Time/International Normalized Ratio (PT/INR).

The prothrombin time (PT) represents the most commonly used coagulation test in clinical laboratories. The PT is mathematically converted to the international normalized ratio (INR) for use in monitoring anticoagulant therapy with vitamin K antagonists such as warfarin in order to provide test results that are adjusted for thromboplastin and instrument used. The INR is created using two major PT 'correction factors', namely the mean normal PT (MNPT) and the international sensitivity index (ISI). Manufacturers of reagents and coagulometers have made some efforts to harmonizing INRs, for example, by tailoring reagents to specific coagulometers and provide associated ISI values. Thus, two types of ISIs may be generated, with one being a 'general' or 'generic' ISI and others being reagent/coagulometer-specific ISI values. Although these play a crucial role in improving INR results between laboratories, these laboratories reported INR values are known to still differ, even when laboratories use the same thromboplastin reagent and coagulometer. Moreover, ISI values for a specific thromboplastin can vary among different models of coagulometers from a manufacturer using the same method for clot identification. All these factors can be sources of error for INR reporting, which in turn can significantly affect patient management. In this narrative review, we provide some guidance to appropriate ISI verification/validation, which may help decrease the variability in cross laboratory reporting of INRs.

Evaluation of STA-NeoPTimal, an extraction thromboplastin reagent with ISI close to 1.

INTRODUCTION: The prothrombin time (PT) is the most requested test to investigate patients with congenital or acquired coagulopathies or to monitor oral anticoagulant therapy. However, thromboplastins can show markedly different responsiveness to the defects induced by vitamin K antagonist (VKA) therapy and are thus characterized by their ISI (International Sensitivity Index). INR results are optimal for patients under VKA but for patients screened for other reasons expressing PT results as ratio can be more appropriate. As it is very difficult to define the PT results reporting unit from the PT testing request, it would be ideal to use a thromboplastin with ISI = 1. The study aims to compare our reference PT reagent with two candidate thromboplastins with ISI close to 1. METHODS: We compared 3 different thromplastins: two rabbit brain extracted based reagents (STA-Neoplastine CI Plus, with ISI = 1.26, routinely used in our laboratory and STA-NeoPTimal with ISI = 1.01) and a recombinant thromboplastin (STA-Neoplastine R with ISI = 0.97). The comparison was done on 175 samples: 75 from individuals without coagulation defects and 100 from patients under VKA. RESULTS: STA-NeoPTimal and STA-Neoplastine R well correlate to our reference, STA-Neoplastine CI Plus: regression equations are y = 1.186x-0.1351, r2  = .9454 and y = 1.1432x-0.1554, r2  = .9951, respectively. The lowest bias on INR results was obtained with STA-NeoPTimal reagent (interval: -0.7/+0.4). CONCLUSION: We conclude that STA-NeoPTimal can be used in the laboratory as it gives results comparable to those obtained with STA-Neoplastine CI Plus. Besides, thanks to its ISI = 1, it guarantees reporting a PT ratio equal to INR which avoids errors.

Evaluation of a new thromboplastin reagent STA-NeoPTimal on a STA R Max analyzer for the measurement of prothrombin time, international normalized ratio and extrinsic factor levels.

INTRODUCTION: We aimed at evaluating the performance of a new prothrombin time (PT) reagent (STA-NeoPTimal) with two other PT reagents (STA-Neoplastine R and STA-Neoplastine CI Plus) and the reference PT reagent used in our laboratory (ReadiPlasTin). METHODS: Evaluation consisted in intra- and interassay precision assessment, determination of sensitivity to unfractionated heparin (UFH) or enoxaparin in spiked samples and to direct oral anticoagulants (DOACs) in patients (n = 43). Method comparison of the 4 PT reagents, factor II, V, VII and X assays was tested on normal (n = 20) and abnormal samples: VKA (n = 47), preoperative (n = 23), liver failure (n = 12) and burned patients (n = 37). RESULTS: Analytical performance met manufacturers' criteria for all reagents. All PT reagents gave correlation coefficients >0.8 and even >0.9 in many situations. In some VKA samples, differences ≥ 0.5 INR units were found in samples within and above therapeutic ranges. For burned patients, PT correlations were good but with some minimal bias (<5.0%) while factor assays gave very consistent results (R > .8 and mainly >0.9). As expected, poor responsiveness of the PT to DOAC concentrations was observed with all four assays. CONCLUSION: The STA-NeoPTimal showed comparable performance to ReadiPlasTin, making it suitable for VKA control, detection of factors II, V, VII, X deficiency and assessment of liver disease coagulopathy. However, for patients receiving VKA, some significant differences were observed. We confirmed the inability of the PT assay to detect residual DOAC concentrations. Finally, burned patients results showed that recombinant thromboplastins were less sensitive to factor deficiencies in comparison to extraction thromboplastins.

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.

Determination of the cut-off prothrombin time to estimate plasma rivaroxaban overdose status.

Laboratory monitoring of rivaroxaban (RIV) is required under certain conditions. Mass spectrometry and anti-factor Xa assays are the recommended methods, which may not be readily available. Prothrombin time (PT) is the most widely used and simple coagulation assay. To set the cutoff PT and international normalized ratio (INR) to estimate RIV overdose status. RIV-spiked pooled normal plasma was used. PT test was performed using a CA-7000 coagulometer and Thromborel S reagent. The precise measurement of RIV concentration at the cut-off PT was evaluated according to the Clinical and Laboratory Standard Institute (CLSI) EP12-A2 guideline. The RIV concentration at 275 ng/mL was analyzed using 40 replicates. Receiver operating characteristic (ROC) analysis was performed to determine the cutoff value for the determination of RIV potential overdose status. An imprecision estimation of PT was conducted with 220.00 ng/mL, 247.50 ng/mL, 261.25 ng/mL, 288.75 ng/mL, 302.50 ng/mL and 330.00 ng/mL concentrations of RIV in 60 replicates. According to the ROC analysis, the cutoff clotting times and INR values to determine the overdose status of RIV were 13.45 s and 1.39. With these values, there was a 92.6% probability that plasma samples with RIV concentration ≤ 247.50 ng/mL yielded consistently negative (on-therapy dose) results, and those with ≥ 302.50 ng/mL yield consistent positive (potential overdose) results using our PT assay. PT with a reliable cutoff clotting time and INR can be used to determine the potential overdose status of RIV to facilitate the diagnosis and treatment by controlling the dose.

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.

Comparison of real world and core laboratory lupus anticoagulant results from the Antiphospholipid Syndrome Alliance for Clinical Trials and International Networking (APS ACTION) clinical database and repository.

BACKGROUND: Variability remains a challenge in lupus anticoagulant (LA) testing. OBJECTIVE: To validate LA test performance between Antiphospholipid Syndrome Alliance for Clinical Trials and International Networking (APS ACTION) Core laboratories and examine agreement in LA status between Core and local/hospital laboratories contributing patients to this prospective registry. METHODS: Five Core laboratories used the same reagents, analyzer type, protocols, and characterized samples for LA validation. Non-anticoagulated registry samples were retested at the corresponding regional Core laboratories and anticoagulated samples at a single Core laboratory. Categorical agreement and discrepancies in LA status between Core and local/hospital laboratories were analyzed. RESULTS: Clotting times for the reference/characterized plasmas used for normalized ratios were similar between Core laboratories (CV <4%); precision and agreement for LA positive/negative plasma were similar (all CV ≤5%) in the four laboratories that completed both parts of the validation exercise; 418 registry samples underwent LA testing. Agreement for LA positive/negative status between Core and local/hospital laboratories was observed in 87% (115/132) non-anticoagulated and 77% (183/237) anticoagulated samples. However, 28.7% (120/418) of samples showed discordance between the Core and local/hospital laboratories or equivocal LA results. Some of the results of the local/hospital laboratories might have been unreliable in 24.7% (41/166) and 23% (58/252) of the total non-anticoagulated and anticoagulated samples, respectively. Equivocal results by the Core laboratory might have also contributed to discordance. CONCLUSIONS: Laboratories can achieve good agreement in LA performance by use of the same reagents, analyzer type, and protocols. The standardized Core laboratory results underpin accurate interpretation of APS ACTION clinical data.

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

Background Correct handling and storage of blood samples for coagulation tests are important to assure correct diagnosis and monitoring. The aim of this study was to assess the pre-analytical practices for routine coagulation testing in European laboratories. Methods In 2013-2014, European laboratories were invited to fill in a questionnaire addressing pre-analytical requirements regarding tube fill volume, citrate concentration, sample stability, centrifugation and storage conditions for routine coagulation testing (activated partial thromboplastin time [APTT], prothrombin time in seconds [PT-sec] and as international normalised ratio [PT-INR] and fibrinogen). Results A total of 662 laboratories from 28 different countries responded. The recommended 3.2% (105-109 mmol/L) citrate tubes are used by 74% of the laboratories. Tube fill volumes ≥90% were required by 73%-76% of the laboratories, depending upon the coagulation test and tube size. The variation in centrifugation force and duration was large (median 2500 g [10- and 90-percentiles 1500 and 4000] and 10 min [5 and 15], respectively). Large variations were also seen in the accepted storage time for different tests and sample materials, for example, for citrated blood at room temperature the accepted storage time ranged from 0.5-72 h and 0.5-189 h for PT-INR and fibrinogen, respectively. If the storage time or the tube fill requirements are not fulfilled, 72% and 84% of the respondents, respectively, would reject the samples. Conclusions There was a large variation in pre-analytical practices for routine coagulation testing in European laboratories, especially for centrifugation conditions and storage time requirements.

Characteristics of scrub typhus, murine typhus, and Q fever among elderly patients: Prolonged prothrombin time as a predictor for severity.

BACKGROUND/PURPOSE: The clinical manifestations of scrub typhus, murine typhus and acute Q fever in the elderly are not clear. METHODS: We conducted a retrospective study to identify the characteristics of the elderly aged ≥65 years with a comparison group aged 18-64 years among patients with scrub typhus, murine typhus, or acute Q fever who were serologically confirmed at three hospitals in Taiwan during 2002-2011. RESULTS: Among 441 cases, including 187 cases of scrub typhus, 166 acute Q fever, and 88 murine typhus, 68 (15.4%) cases were elderly patients. The elderly had a higher severe complication rate (10.3% vs. 3.5%, p = 0.022), but did not have a significantly higher mortality rate (1.47% vs. 0.54%, p = 0.396). Compared with those without severe complications, we found the elderly (p = 0.022), dyspnea (p = 0.006), less relative bradycardia (p = 0.004), less febrile illness (p = 0.004), prolonged prothrombin time (PT) (p = 0.002), higher levels of initial C-reactive protein (p = 0.039), blood leukocyte counts (p = 0.01), and lower platelet counts (p = 0.012) are significantly associated with severe complications. Only prolonged prothrombin time was associated with severe complications in multivariate analysis (p = 0.018, CI 95% 0.01-0.66). Among clinical symptoms and laboratory data, multivariate analysis revealed chills was less frequently occurred in the elderly (p = 0.012, 95% confidence interval [CI]: 1.33-9.99). CONCLUSION: The elderly cases with scrub typhus, murine typhus, or acute Q fever would be more likely to have severe complications, for which prothrombin time prolongation is an important predictor for severe complications.

Dilute Russell viper venom time interpretation and clinical correlation: A two-year retrospective institutional review.

INTRODUCTION: The dilute Russell viper venom time (dRVVT) detects lupus anticoagulant (LA). International Society for Thrombosis and Haemostasis (ISTH) guidelines specify positivity criteria, which differ from the assay manufacturer's criteria. METHODS: Two years of dRVVT testing at our institution were reviewed. For patients with prolonged dRVVT screening times, we evaluated dRVVT results by ISTH and manufacturer's criteria and correlated with the results of other antiphospholipid syndrome (APS) testing (LA-sensitive activated partial thromboplastin time and antiphospholipid antibodies) and with history of thromboembolism and other APS manifestations. RESULTS: Approximately one-fifth of dRVVTs exhibited a prolonged screening time. Among first prolonged dRVVTs, 35% were positive by both ISTH and manufacturer criteria, 44% met neither criteria, and 20% were equivocal (positive by only ISTH or manufacturer). Positivity by ISTH guidelines alone correlated better with other positive APS tests than manufacturer criteria positivity. Positive dRVVTs by both criteria correlated even more strongly with other positive APS assays. We investigated the likelihood of eventual APS diagnosis depending on the testing indication. No patient tested for LA solely for prolonged screening aPTT was subsequently diagnosed with APS. In patients with thrombosis, prolonged dRVVT clotting time not meeting both ISTH and manufacturer criteria was rarely associated with eventual APS diagnosis. CONCLUSION: We examined the correlation of dRVVT results with other APS testing and clinical outcomes. Interpretation method impacted how dRVVT results related to other APS testing, and, in limited data, to clinical findings. Patients with prolonged dRVVTs meeting only one set of positivity criteria rarely received an APS diagnosis.

Biological variation estimates of prothrombin time, activated partial thromboplastin time, and fibrinogen in 28 healthy individuals.

BACKGROUND: Although tests of global hemostasis prothrombin time (PT) and activated partial thromboplastin time (aPTT) should not be used for prediction of bleeding risk, these tests are often used by many clinicians in daily practice particularly as a preoperative screening test. Robust biological variation (BV) data are needed for safe clinical applications of these tests. In this study, a stringent protocol was followed to estimate the BV's for PT, aPTT, and fibrinogen levels. METHODS: Weekly blood samples were obtained from 28 healthy individuals (18 females, 10 males) during 10 weeks study period. All measurements were performed with Stago STA-R coagulation analyzer. Prior to coefficient of variation (CV)-analysis of variance (ANOVA), the data were assessed for normality, trends, outliers, and variance homogeneity. Sex-stratified within-individual (CVI ) and between-individual (CVG ) BV estimates were determined for PT, aPTT, and fibrinogen tests. RESULTS: No difference was found between male and female estimates of BV. The observed CVI and CVG estimates were found to be lower than those previously published. Only for fibrinogen, CVI was higher than CVG . CONCLUSION: Following a meticulous protocol, our study results provide up-to-date and more stringent BV estimates of global hemostasis tests.