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.

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.

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.

A Comparative Study of Point-of-Care Prothrombin Time in Cardiopulmonary Bypass Surgery.

OBJECTIVE: Point-of-care (POC) devices allow for prothrombin time/international normalized ratio (PT/INR) testing in whole blood (WB) and timely administration of plasma or prothrombin complex concentrate during cardiopulmonary bypass surgery. This study evaluated the sensitivities of a new POC PT test, a dry-hematology method with heparin neutralization technology (DRIHEMATO PT-S [DRI PT-S]; A&T Corporation, Kanagawa, Japan), and compared it with other POC tests currently available. DESIGN: Prospective, observational study. SETTING: University hospital, single center. PARTICIPANTS: Healthy volunteers and warfarin-treated and cardiac surgical patients. MEASUREMENT AND MAIN RESULTS: In WB samples obtained from 6 healthy volunteers, PT-INR results of DRI PT-S were not affected by an in vitro addition of heparin <6.0 U/mL. In warfarin-treated samples (n = 88, PT/INR 0.98-3.87), PT-INR with DRI PT-S showed acceptable correlation with the laboratory method (r2 = 0.85, p < 0.001). In blood samples obtained from cardiac surgical patients (n = 72), heparin prolonged the PT/INR with the laboratory assay, dry-hematology method with non heparin neutralization technology (DRI PT), Coaguchek XS (Roche Diagnostics, Basel, Switzerland), and Hemochron Jr. (Accriva Diagnostics, Edison, NJ), but DRI PT-S was not affected by heparin anticoagulation. In nonheparinized samples, different methods between DRI PT-S and the laboratory method yielded acceptable correlations (r2 = 0.76, p < 0.0001). There was a moderate correlation between factor levels and the PT-INR with DRI PT-S (factor [F]II: r2 = 0.63, FVII: r2 = 0.47, FX: r2 = 0.67; p < 0.0001). CONCLUSIONS: This study demonstrated that PT/INR can be accurately assessed using the dry-hematology method in WB under therapeutic heparin levels. Currently available other POC PT/INR tests are affected by heparin, and thus they are not recommended for coagulation monitoring during cardiopulmonary bypass.

The impact of frequency of patient self-testing of prothrombin time on time in target range within VA Cooperative Study #481: The Home INR Study (THINRS), a randomized, controlled trial.

Anticoagulation (AC) is effective in reducing thromboembolic events for individuals with atrial fibrillation (AF) or mechanical heart valve (MHV), but maintaining patients in target range for international normalized ratio (INR) can be difficult. Evidence suggests increasing INR testing frequency can improve time in target range (TTR), but this can be impractical with in-clinic testing. The objective of this study was to test the hypothesis that more frequent patient-self testing (PST) via home monitoring increases TTR. This planned substudy was conducted as part of The Home INR Study, a randomized controlled trial of in-clinic INR testing every 4 weeks versus PST at three different intervals. The setting for this study was 6 VA centers across the United States. 1,029 candidates with AF or MHV were trained and tested for competency using ProTime INR meters; 787 patients were deemed competent and, after second consent, randomized across four arms: high quality AC management (HQACM) in a dedicated clinic, with venous INR testing once every 4 weeks; and telephone monitored PST once every 4 weeks; weekly; and twice weekly. The primary endpoint was TTR at 1-year follow-up. The secondary endpoints were: major bleed, stroke and death, and quality of life. Results showed that TTR increased as testing frequency increased (59.9 ± 16.7 %, 63.3 ± 14.3 %, and 66.8 ± 13.2 % [mean ± SD] for the groups that underwent PST every 4 weeks, weekly and twice weekly, respectively). The proportion of poorly managed patients (i.e., TTR <50 %) was significantly lower for groups that underwent PST versus HQACM, and the proportion decreased as testing frequency increased. Patients and their care providers were unblinded given the nature of PST and HQACM. In conclusion, more frequent PST improved TTR and reduced the proportion of poorly managed patients.

The Quick Test: 80 years on.

Few procedures have lasted as long as the Quick Test and its later variants, but cardiologists should not accept anticoagulation data without first checking that reliable methods are being used, according to haematologist Prof. Leon Poller MD, Faculty of Life Sciences, Manchester, UK.

Local verification and assignment of mean normal prothrombin time and International Sensitivity Index values across various instruments: recent experience and outcome from North America.

Warfarin dosing relies on accurate measurements of international normalized ratio (INR), which is calculated from the prothrombin time (PT), International Sensitivity Index international sensitivity index (ISI) of the thromboplastin, and the geometric mean of normal PT (MNPT). However, ISI assignments of certain reagent/instrument combinations are frequently unavailable, especially when the reagent and instrument are not from the same manufacturer. The effort to be in compliance with widely endorsed Clinical and Laboratory Standards Institute (CLSI) guidelines by locally verifying or assigning an ISI to an unsupported reagent/instrument combination is further hindered by the lack of US Food and Drug Administration (FDA)-approved certified plasmas designated for a particular reagent/instrument combination. The objectives of the study include development of a process to verify/assign ISI and MNPT of a single thromboplastin reagent from one manufacturer across multiple instruments including several from another manufacturer and across several campuses of a single institution, the Mayo Clinic. In this study, RecombiPlasTin 2G (R2G), was evaluated on the ACL TOP 700 (IL), STA-R Evolution, STA Compact, and STA Satellite. Random normal donor samples (n = 25) were used to verify/assign MNPT. A subset of the normal donors (n = 8) and 13 warfarin pools (INR range: 1.3-3.9), created from stable warfarin patient plasma, were used for ISI verification/assignment. The manufacturer's assigned ISI was first verified on the ACL TOP 700 (reference method), then assigned on three unsupported instruments using orthogonal regression analysis. The MNPT and manufacturer assigned ISI (11.0, 0.95) were verified on the ACL TOP 700 and subsequently assigned on the STA-R Evolution (11.6, 1.04); STA Compact (11.5, 1.02); and STA Satellite (10.9, 0.99). Linear correlations of the INR results from all the four instruments demonstrated an r2 > 0.99. This process provides a reproducible approach to assigning ISIs on unsupported reagent/instrument combinations. Our data also confirm that ISIs of the same PT reagent differ significantly on different instruments, thus confirming the requirement for evaluations and validation of ISIs for different reagent/instrument combinations.

International normalized ratio testing with point-of-care coagulometer in healthy term neonates.

BACKGROUND: Neonates routinely receive vitamin K to prevent vitamin K deficiency bleeding, which is associated with a high mortality rate and a high frequency of neurological sequelae. A coagulation screening test might be necessary to detect prophylactic failure or incomplete prophylaxis. However, venous access and the volume of blood required for such testing can be problematic. CoaguChek XS is a portable device designed to monitor prothrombin time while only drawing a small volume of blood. Although the device is used in adults and children, studies have not been performed to evaluate its clinical utility in neonates, and the reference value is unknown in this population. The objectives of the present study were to determine the reference intervals (RIs) for international normalized ratio (INR) using the CoaguChek XS by capillary puncture in healthy term neonates, to evaluate factors that correlate with INR, and to evaluate the device by assessing its ease of use in clinical practice. METHODS: This study included 488 healthy term neonates born at a perinatal center between July 2012 and June 2013. The INRs determined by CoaguChek XS were measured in 4-day-old neonates. RESULTS: The enrolled neonates were orally administered vitamin K 6-12 h after birth. A RI for INRs in 4-day-old neonates was established using the CoaguChek XS with a median value of 1.10 and a range of 0.90-1.30. A significant difference in the INR was noted between male (median value, 1.10; RI, 0.90-1.30) and female (median value, 1.10; RI, 0.90-1.24) neonates (p = 0.049). The INR was found to correlate with gestational age, birth weight, and hematocrit value. CONCLUSIONS: The CoaguChek XS device is safe, fast, and convenient for performing INR assays in neonates. Our study is the first to establish a RI for INRs that were measured using the CoaguChek XS in healthy term neonates.

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.

Do elevated hematocrits prolong the PT/aPTT?

The Clinical and Laboratory Standards Institute guidelines require special processing of whole blood specimens with hematocrits greater than 55% due to the possibility of spurious prolongation of routine coagulation studies (PT, aPTT). As samples with hematocrits above 60% are rare at our institution, our study seeks to determine the effect of relative citrate excess on routine coagulation studies in samples with hematocrits of 60% to determine whether special processing is necessary. A calculated volume of 3.2% citrate was added to 1 mL aliquots of 40 whole blood samples in citrated tubes from adult patients to simulate a hematocrit of 60%. A dilutional control was created by adding an equivalent volume of saline to a separate 1 mL aliquot. Routine coagulation studies (PT, aPTT) were run on both samples on the STA Compact Analyzer in accordance with manufacturer instructions. While a paired Student's t-test demonstrated a clinically significant change in both PT and aPTT with the addition of citrate (p = 0.0002 for PT and p = 0.0234 for aPTT), clinical management would not have been altered by any observed change. More interestingly, we observed a shortening of 27/40 PTs and 23/40 aPTTs rather than the expected prolongation. Based on our data, no adjustment of citrate volume appears to be necessary in samples with hematocrits less than or equal to 60%.

Quality standards for sample collection in coagulation testing.

Preanalytical activities, especially those directly connected with blood sample collection and handling, are the most vulnerable steps throughout the testing process. The receipt of unsuitable samples is commonplace in laboratory practice and represents a serious problem, given the reliability of test results can be adversely compromised following analysis of these specimens. The basic criteria for an appropriate and safe venipuncture are nearly identical to those used for collecting blood for clinical chemistry and immunochemistry testing, and entail proper patient identification, use of the correct technique, as well as appropriate devices and needles. There are, however, some peculiar aspects, which are deemed to be particularly critical when collecting quality specimens for clot-based tests, and these require clearer recognition. These include prevention of prolonged venous stasis, collection of nonhemolyzed specimens, order of draw, and appropriate filling and mixing of the primary collection tubes. All of these important preanalytical issues are discussed in this article, and evidence-based suggestions as well as recommendations on how to obtain a high-quality sample for coagulation testing are also illustrated. We have also performed an investigation aimed to identify variation of test results due to underfilling of primary blood tubes, and have identified a clinically significant bias in test results when tubes are drawn at less than 89% of total fill for activated partial thromboplastin time, less than 78% for fibrinogen, and less than 67% for coagulation factor VIII, whereas prothrombin time and activated protein C resistance remain relatively reliable even in tubes drawn at 67% of the nominal volume.

Quality standards for sample processing, transportation, and storage in hemostasis testing.

Samples for hemostasis testing drawn into sodium citrate anticoagulant are vulnerable to the effects of preanalytical variables associated with sample processing, transportation, and storage. These variables include the temperature at which samples are transported and stored; the stability of the samples once processed; whether maintained at room temperature, refrigerated, or frozen; methods of centrifugation; as well as the potential impact of using an automated line. Acknowledgment of these variables, as well as understanding their potential impact on assay results, is imperative to the reporting of high quality and accurate results. This article discusses the preanalytical issues associated with sample processing, transportation, and storage and also presents the ideal conditions for sample handling.

Approaches to investigating common bleeding disorders: an evaluation of North American coagulation laboratory practices.

Bleeding disorders commonly result from deficiencies or defects in von Willebrand factor (VWF), platelets, coagulation factors, or fibrinolytic proteins. The primary goal of our study was to assess current North American coagulation laboratory practices for diagnosing bleeding disorders, using an on-line patterns-of-practice survey of diagnostic laboratory members of the North American Specialized Coagulation Laboratory Association. The survey examined laboratory approaches to evaluating bleeding disorders, with specific questions about the tests and test panels offered and compliance to recent guideline recommendations on diagnosing von Willebrand disease (VWD) and platelet function disorders. All laboratories responding to the survey performed a prothrombin time/international normalized ratio, an activated partial thromboplastin time, and coagulation factor assays, and many tested for VWD and platelet disorders. However, few laboratories had test panels that evaluated the more common bleeding disorders and few performed some assays, including VWF multimer assessments and assays for fibrinolytic disorders. Additionally, the cutoffs used by laboratories to diagnose type 1 VWD varied considerably, with only a minority following the National Heart Lung Blood Institute recommendations. In contrast, laboratories that tested for platelet function disorders mostly complied with aggregation testing recommendations, as published in the recent North American guidelines. Our results indicate that there are some gaps in the strategies used by laboratories to diagnose bleeding disorders that might be addressed by development of further guidelines and test algorithms that emphasize evaluations for common bleeding disorders. Laboratories may also benefit from guidelines on test interpretation, and external evaluation of their bleeding disorder testing strategies.

On the value of routine prothrombin time screening in elective neurosurgical procedures.

OBJECT: The authors performed a study to evaluate whether preoperative assessment of prothrombin time (PT) is mandatory in patients undergoing routinely planned neurosurgical procedures. METHODS: The charts of all patients admitted to general wards of the authors' department for routinely planned surgery (excluding trauma and ICU patients) between 2006 and 2010 were retrospectively reviewed. The authors assessed preoperative PT and the clinical courses of all patients, with special consideration for patients receiving coagulation factor substitution. All cases involving hemorrhagic complications were analyzed in detail with regard to pre- and postoperative PT abnormalities. Prothrombin time was expressed as the international normalized ratio, and values greater than 1.28 were regarded as elevated. RESULTS: Clinical courses and PT values of 4310 patients were reviewed. Of these, 33 patients (0.7%) suffered hemorrhagic complications requiring repeat surgery. Thirty-one patients (94%) had a normal PT before the initial operation, while 2 patients had slightly elevated PT values of 1.33 and 1.65, which were anticipated based on the patient's history. In the latter 2 cases, surgery was performed without prior correction of PT. Preoperatively, PT was elevated in 78 patients (1.8%). In 73 (93.6%) of the 78 patients, the PT elevation was expected and explained by each patient's medical history. In only 5 (0.1%) of 4310 patients did we find an unexpected PT elevation (mean 1.53, range 1.37-1.74). All 5 patients underwent surgery without complications, while 2 had received coagulation factor substitution preoperatively, as requested by the surgeon, because of an estimated risk of bleeding complications. None of the 5 patients received coagulation factor substitution postoperatively, and later detailed laboratory studies ruled out single coagulation factor deficiencies. There was no statistically significant association between preoperatively elevated PT levels and the occurrence of hemorrhagic complications (p = 0.12). Before the second procedure but not before the initial operation, 4 (12%) of the 33 patients had elevated PT. CONCLUSIONS: The findings suggest that the value of preoperative PT testing is limited in patients in whom a normal history can be ascertained. Close postoperative PT control is necessary in every neurosurgical patient, and better tests need to be developed to identify patients who are prone to hemorrhagic complications.