Anti-factor Xa Assay Research Articles

In vitro and in vivo characterization of a reversible synthetic heparin analog

BackgroundThe global supply of unfractionated heparin (UFH) and all commercially available low molecular weight heparins (LMWH) remain dependent on animal sources, such as porcine intestine or bovine lung. Recent experience has shown that contamination of the supply chain (with over-sulfated chondroitin sulfates) can result in lethal toxicity. Fondaparinux is currently the only commercially available synthetic analog of heparin. We recently described a new class of chemoenzymatically synthesized heparin analogs. One of these compounds (S12-mer) is a dodecasaccharide consisting of an antithrombin-binding moiety with repeating units of IdoA2S-GlcNS6S and two 3-O-sulfate groups that confer the ability to bind protamine. Objective/methodsWe sought to further characterize this new compound in vitro using biochemical and global coagulation assays and in vivo using thrombosis and hemostasis assays. ResultsThe anticoagulant activities of the Super 12-mer (S12-mer) and Enoxaparin in anti-factor Xa and plasma-based thrombin generation assays were roughly equivalent with a 50% reduction in peak thrombin generation occurring at approximately 325nM. When protamine was titrated against a fixed concentration of S12-mer in plasma or blood, the S12-mer displayed a significant restitution of thrombin generation and clot formation. In vivo, S12-mer inhibited venous thrombosis to a similar extent as Enoxaparin, with similar bleeding profiles. ConclusionsThese data show that the S12-mer has almost identical efficacy to Enoxaparin in terms of FXa inhibition, while displaying significant reversibility with protamine. Taken together with the ability to ensure purity and homogeneity from batch to batch, the S12-mer is a promising new synthetic heparin analog with a potentially enhanced safety profile.

Circulation : Clinical Summaries

<i>Circulation</i> : Clinical Summaries

Clinical implication of monitoring rivaroxaban and apixaban by using anti-factor Xa assay in patients with non-valvular atrial fibrillation

BackgroundAlthough patients taking non-vitamin K antagonist oral anticoagulants (NOACs) do not require routine coagulation monitoring, high-risk patients require monitoring to assess pharmacodynamics. MethodsWe measured (1) anti-factor Xa activity (AXA), using chromogenic assay with the HemosIL Liquid Heparin kit, (2) prothrombin time (PT), and (3) activated partial thromboplastin time (aPTT) in 188 blood samples from 70 patients with non-valvular atrial fibrillation, of whom 36 received rivaroxaban once daily and 34 received apixaban twice daily. ResultsAfter the rivaroxaban therapy, AXA ranged from 0 to 3.65IU/mL; PT, from 9.6 to 44.5s; and APTT, from 19.3 to 69.7s. After the apixaban therapy, AXA ranged from 0.02 to 3.18IU/mL; PT, from 10.2 to 20.8s; and APTT, from 21.8 to 59.8s. At peak time, the AXA of patients who received rivaroxaban and apixaban were almost the same (2.08±0.91IU/mL vs. 1.71±0.57IU/mL), but the PT and APTT of patients who received rivaroxaban were more prolonged than those of patients who received apixaban (18.1±5.6s vs. 13.8±0.9s, p<0.001 and 40.9±7.3s vs. 35.5±7.5s, p<0.01, respectively). At trough time, the AXA and PT of patients who received rivaroxaban were respectively lower and shorter than those of patients who received apixaban (0.28±0.31IU/mL vs. 1.04±0.72IU/mL, p<0.001 and 11.9±2.0s vs. 13.7±2.4s, p<0.01, respectively), but the APTT of patients who received rivaroxaban and apixaban did not significantly differ (32.3±4.3s vs. 34.3±3.8s). ConclusionsMeasurement of AXA might be useful to assess the pharmacodynamics of high-risk patients, such as high age, low body weight, and/or low renal function, and to assess the intensity of anticoagulation by using different methods of administration, such as crushed tablet via the nasogastric tube.

Comparison of unfractionated heparin protocols using antifactor Xa monitoring or activated partial thrombin time monitoring.

To determine whether there is a difference between an activated partial thromboplastin time (aPTT) based unfractionated heparin (UFH) protocol versus an antifactor Xa based UFH protocol with respect to 24-hour attainment of therapeutic levels. This was an observational study performed at a 500 bed private, community hospital. The study included inpatients from January 2008 to December 2009 on our institution's aPTT UFH protocol and inpatients from July 2010 to March 2011 on our institution's antifactor Xa UFH protocol. The two groups were compared to determine whether a higher percentage of patients reached therapeutic goal within 24 hours of UFH initiation. Secondary outcomes evaluated the percentage of patients at therapeutic goal within 6 and 12 hours, incidence of bleeding, and number of UFH dosage adjustments within 24 hours between the two groups. One hundred twenty-one patients met inclusion criteria for this study; 79 in the aPTT group and 42 in the antifactor Xa group. At 24 hours, 74% of patients in the antifactor Xa group were at goal, versus 63% of patients in the aPTT group (p = 0.242). Nearly 57% of patients in the antifactor Xa group were at goal versus 27% in the aPTT group within 6 hours (p = 0.001). Subjects in the antifactor Xa group averaged 1.00 dosage adjustments per subject as compared to an 1.71 dosage adjustments per subject in the aPTT group within the first 24 hours (p = 0.003). The antifactor Xa assay should be used to monitor UFH versus aPTT due to less variability in measurements, the absence of a need for calibration with new reagents/coagulometers, quicker attainment of therapeutic levels, fewer dose adjustments, and similar bleeding rates.

Heparin-Calibrated Chromogenic Anti-Xa Activity Measurements in Patients Receiving Rivaroxaban: Can This Test Be Used to Quantify Drug Level?

Determination of plasma rivaroxaban concentration may be necessary in certain clinical situations. Rivaroxaban concentration can be accurately and rapidly determined using a chromogenic anti-activated factor X (factor Xa) assay with specific drug calibrator material. However, there are currently no Food and Drug Administration (FDA)-approved rivaroxaban calibrators available in the United States. To determine whether FDA-approved commercial kits for measuring heparin anti-factor Xa activity can be used to assess rivaroxaban concentrations when calibrated for unfractionated heparin or low-molecular-weight heparins. Trough and peak samples were taken from 30 patients taking rivaroxaban as part of their routine care for atrial fibrillation or venous thromboembolism. The samples were tested using 3 different FDA-approved commercial kits for measuring heparin anti-factor Xa activity. There was acceptable correlation between rivaroxaban levels and heparin anti-factor Xa activity using Berichrom and COAMATIC heparin kits. The STA liquid heparin method was the most sensitive to presence of rivaroxaban. This study demonstrates a strong correlation, but variability between kits, for assessing rivaroxaban concentrations using heparin anti-factor Xa assays. The extent of the heparin calibration curve significantly limits the measurable rivaroxaban range, and this application may be useful only for trough samples. The STA liquid heparin, being exquisitely sensitive to rivaroxaban, may be suitable for ruling out presence of the drug. The routine use of heparin-calibrated anti-factor Xa assays to quantify rivaroxaban is not advocated, and when applied, it must be used with caution and limitations clearly understood.

Using New Oral Anticoagulants in Patients Undergoing Major Orthopedic Surgery

Four new oral anticoagulants (NOAC), apixaban, rivaroxaban, edoxaban, and dabigatran, are now available in the USA; however, only apixaban and rivaroxaban are FDA approved for the prevention of venous thromboembolism following orthopedic surgery. Apixaban, rivaroxaban, and edoxaban's anticoagulant activity can be measured using a chromogenic anti-factor Xa assay but there is no widely available means of measuring dabigatran blood levels. None of the NOAC has an antidote. Dabigatran is 80% renally excreted, and patients with atrial fibrillation taking dabigatran for stroke prevention should stop the drug 4-5 days prior to major orthopedic surgery. Apixaban, rivaroxaban, and edoxaban should be held for 48 h preoperatively in this setting.

Measuring anti-factor xa activity to monitor low-molecular-weight heparin in obesity: a critical review.

The choice of whether to monitor anti-factor Xa (anti-Xa) activity in patients who are obese and who are receiving low-molecular-weight heparin (LMWH) therapy is controversial. To the authors' knowledge, no systematic review of monitoring of anti-Xa activity in such patients has been published to date. To systematically ascertain the utility of monitoring anti-Xa concentrations for LMWH therapy in obese patients. MEDLINE (1946 to September 2014), the Cochrane Database of Systematic Reviews, Embase (1974 to September 2014), PubMed (1947 to September 2014), International Pharmaceutical Abstracts (1970 to September 2014), and Scopus were searched using the terms obesity, morbid obesity, thrombosis, venous thrombosis, embolism, venous thromboembolism, pulmonary embolism, low-molecular weight heparin, enoxaparin, dalteparin, tinzaparin, anti-factor Xa, anti-factor Xa monitoring, anti-factor Xa activity, and anti-factor Xa assay. The reference lists of retrieved articles were also reviewed. English-language studies describing obese patients treated with LMWH or reporting anti-Xa activity were reviewed using a 9-step decision-making algorithm to determine whether monitoring of LMWH therapy by means of anti-Xa activity in obesity is warranted. Studies published in abstract form were excluded. The analysis showed that anti-Xa concentrations are not strongly associated with thrombosis or hemorrhage. In clinical studies of LMWH for thromboprophylaxis in bariatric surgery, orthopedic surgery, general surgery, and medical patients, and for treatment of venous thrombo embolism and acute coronary syndrome, anti-Xa activity can be predicted from dose of LMWH and total body weight; no difference in clinical outcome was found between obese and non-obese participants. Routinely determining anti-Xa concentrations in obese patients to monitor the clinical effectiveness of LMWH is not warranted on the basis of the current evidence. Circumstances where measurement of anti-Xa concentration may help in clinical decision-making in either obese or non-obese patients would be cases where elimination of LMWH is impaired or there is an unexpected clinical response, as well as to confirm compliance with therapy or to identify deviation from predicted pharmacokinetics.

Monitoring low molecular weight heparins at therapeutic levels: dose-responses of, and correlations and differences between aPTT, anti-factor Xa and thrombin generation assays.

BackgroundLow molecular weight heparins (LMWH’s) are used to prevent and treat thrombosis. Tests for monitoring LMWH’s include anti-factor Xa (anti-FXa), activated partial thromboplastin time (aPTT) and thrombin generation. Anti-FXa is the current gold standard despite LMWH’s varying affinities for FXa and thrombin.AimTo examine the effects of two different LMWH’s on the results of 4 different aPTT-tests, anti-FXa activity and thrombin generation and to assess the tests’ concordance.MethodEnoxaparin and tinzaparin were added ex-vivo in concentrations of 0.0, 0.5, 1.0 and 1.5 anti-FXa international units (IU)/mL, to blood from 10 volunteers. aPTT was measured using two whole blood methods (Free oscillation rheometry (FOR) and Hemochron Jr (HCJ)) and an optical plasma method using two different reagents (ActinFSL and PTT-Automat). Anti-FXa activity was quantified using a chromogenic assay. Thrombin generation (Endogenous Thrombin Potential, ETP) was measured on a Ceveron Alpha instrument using the TGA RB and more tissue-factor rich TGA RC reagents.ResultsMethods’ mean aPTT at 1.0 IU/mL LMWH varied between 54s (SD 11) and 69s (SD 14) for enoxaparin and between 101s (SD 21) and 140s (SD 28) for tinzaparin. ActinFSL gave significantly shorter aPTT results. aPTT and anti-FXa generally correlated well. ETP as measured with the TGA RC reagent but not the TGA RB reagent showed an inverse exponential relationship to the concentration of LMWH. The HCJ-aPTT results had the weakest correlation to anti-FXa and thrombin generation (Rs0.62–0.87), whereas the other aPTT methods had similar correlation coefficients (Rs0.80–0.92).ConclusionsaPTT displays a linear dose-respone to LMWH. There is variation between aPTT assays. Tinzaparin increases aPTT and decreases thrombin generation more than enoxaparin at any given level of anti-FXa activity, casting doubt on anti-FXa’s present gold standard status. Thrombin generation with tissue factor-rich activator is a promising method for monitoring LMWH’s.

The use of an extracorporeal membrane oxygenation anticoagulation laboratory protocol is associated with decreased blood product use, decreased hemorrhagic complications, and increased circuit life.

To determine if a comprehensive extracorporeal membrane oxygenation anticoagulation monitoring protocol results in fewer hemorrhagic complications, reduced blood product usage, and increased circuit life. In September 2011, we augmented our standard extracorporeal membrane oxygenation laboratory protocol to include anti-factor Xa assays, thromboelastography, and antithrombin measurements. We performed a retrospective chart review to determine outcomes for patients placed on extracorporeal membrane oxygenation prior to and after the initiation of our anticoagulation laboratory protocol. Tertiary care, academic children's hospital. All patients who were placed on extracorporeal membrane oxygenation at our institution from January 1, 2007, to September 30, 2013. None. There were 261 extracorporeal membrane oxygenation runs before the initiation of the protocol and 105 extracorporeal membrane oxygenation runs after the initiation of the protocol. There were no major changes to our extracorporeal membrane oxygenation circuit or changes to our transfusion threshold during the study period. The indication for extracorporeal membrane oxygenation, age, and severity of illness of the patients were similar before and after protocol initiation. Median blood product usage for packed RBCs, fresh frozen plasma, platelets, and cryoprecipitate decreased significantly after protocol initiation. The occurrence of cannula site bleeding decreased from 22% to 12% (p = 0.04), and surgical site bleeding decreased from 38% to 25% (p = 0.02). Median extracorporeal membrane oxygenation circuit life increased from 3.6 to 4.3 days (p = 0.02). A trend toward increased patient survival was noted, but it did not reach statistical significance. We demonstrate an association between an extracorporeal membrane oxygenation anticoagulation laboratory protocol using anti-factor Xa assays, thromboelastography, and antithrombin measurements and a decrease in blood product transfusion, a decrease in hemorrhagic complications, and an increase in circuit life. To our knowledge, this is the first study to demonstrate clinical benefit associated with the use of these laboratory values for patients on extracorporeal membrane oxygenation.

Direct oral anticoagulants: new drugs and new concepts.

Direct oral anticoagulants (DOACs) are approved for multiple thromboembolic disorders and provide advantages over existing agents. As with all anticoagulants, management protocols for the eventuality of bleeding are important. Randomized phase III studies generally show that DOACs have a similar risk of clinically relevant bleeding compared with standard anticoagulants, with reductions in major bleeding in some cases. This may be particularly important in patients with atrial fibrillation, for whom the rate of intracranial hemorrhage was approximately halved with DOACs compared with warfarin. Conversely, the risk of gastrointestinal bleeding may be increased. Specific patient characteristics, such as renal impairment, comedications, and particular aspects of each drug, including the proportion eliminated by the kidneys, must be taken into account when assessing the risk of bleeding. Although routine coagulation monitoring of DOACs is not required, it may be useful under some circumstances. Of the traditional clotting assays, a sensitive and calibrated prothrombin time may be useful for detecting the presence or absence of clinically relevant factor Xa inhibitor concentrations (rivaroxaban or apixaban), but specific anti-factor Xa assays can measure drug levels quantitatively. For dabigatran, the results of an activated partial thromboplastin time test may exclude a clinically relevant pharmacodynamic effect, but a calibrated dilute thrombin time assay can be used for quantification of drug levels. In the event of mild or moderate bleeding, normal hemostatic support measures are recommended. For life-threatening bleeding, use of nonspecific prohemostatic agents may be considered, although clinical evidence is scarce. Specific antidotes are in development.

Comparison of Methods to Determine Rivaroxaban anti-factor Xa activity

Background and ObjectivesRivaroxaban, a new oral anti-Xa agent, has been approved for use without routine monitoring, but the lack of a predictable drug level measurement may hinder the management of anticoagulated patients. The aims of the project were to correlate a Anti-Factor Xa assay using commercial calibrators and controls (Riva Activity) with serum drug levels analyzed by HPLC-MS/MS (Riva MS) in patients currently receiving rivaroxaban, and secondly, to correlate the PT/PTT, thrombin generation (CAT assay) and Thromboelastograph (TEG) with the Riva activity and Riva MS. MethodsRecruited patients receiving rivaroxaban prospectively had a total of 3 blood samples taken at least 2hours apart. Plasma was divided for measurement of PT/PTT, Riva activity, rivaroxaban HPCL-MS/MS, and thrombin generation. TEG activity was measured at one random time point for each patient. Correlation and linear regression evaluations were used to compare the different assays. ResultsThe cases were 22 patients on rivaroxaban, age 56+12.6, and 10 healthy controls. There was a strong correlation between Riva activity compared to serum Riva MS (r=0.99). We found a statistically significant correlation between PT/INR compared to serum measurements of Riva MS (r=0.68) and anti-Xa activity (r=0.69). The peak (r=-0.50) and lag time (r=0.57) CAT correlated with Riva MS measurements. There was no correlation between Riva MS and PTT, TEG R, TEG MA, Endogenous Thrombin potential. ConclusionRiva anti-factor Xa activity assay measured with commercial calibrators and controls provides a reliable assessment of rivaroxaban serum levels for patients requiring measurement of anticoagulant activity. Correlation with other coagulation tests is not sufficiently strong to be used clinically.

Correlation between aPTT and antifactor Xa to determine therapeutic ranges for unfractionated heparin

The therapeutic range (TR) of activated partial thromboplastin time (aPTT) for unfractionated heparin (UFH) dosing was established in the 1970 decade. Since then aPTT determination has changed. Current TR may be sub or supra-therapeutic depending on the reagents of the test, and therefore, responsible for complications of therapy. To establish the TR for UFH dosing in our institution using antifactor Xa analysis as reference standard. After obtaining an informed consent, 43 blood samples were obtained for aPTT determination and antifactor Xa assay in 23 patients treated with intravenous UFH. Samples were processed at Emergency and Hemostasis Labs. We excluded patients receiving other anticoagulants, with thrombophilia, pregnancy or liver disease. Mean aPTT values in the Hemostasis and Emergency labs ​​were 57.1 ± 18.9 and 56.6 ± 18.3 seconds, respectively (p = 0.77). The squared correlation coefficients between aPTT and antifactor Xa at hemostasis and emergency labs were R2 0.5 and 0.45 respectively, p < 0.001. Using a linear regression analysis, therapeutic aPTT range values ​​in our laboratory were established between 50 and 80 seconds, corresponding to antifactor Xa values of 0.3 to 0.7 IU/mL. According to current recommendations, validation of aPTT determination with reference techniques should be done in every institution.

The in-vitro anticoagulant effect of rivaroxaban in neonates

The use of anticoagulants in neonates is increasing because of the medical advances improving the long-term survival of very sick infants who are at risk of venous thromboembolism (VTE). Current anticoagulation therapy in neonates is less than ideal, because of the physiological differences compared to children and adults regarding the pathophysiology of thrombosis and pharmacology of the drug. Limitations associated with conventional anticoagulants have prompted the development of novel drugs that specifically target the key proteins in the coagulation system. Rivaroxaban is the first oral, direct Factor Xa inhibitor available for the prevention of VTE in adults. Its predictable pharmacokinetic profile, high oral bioavailability and once-daily dosing make rivaroxaban an optimal anticoagulant that warrants investigation in neonates. This study was designed to determine whether there are age-related differences in the pharmacodynamic effects of rivaroxaban in vitro amongst neonates. Neonatal and adult plasma pools were created and spiked with increasing concentrations of rivaroxaban (0-500 ng/ml). Commercially available prothrombin time (PT), activated partial thromboplastin time (aPTT) and anti-Factor Xa assays as well as a sub-sampling thrombin generation assay were used to measure the rivaroxaban effect. A dose-dependent response was observed for PT, aPTT and lag time in both the age groups. Rivaroxaban caused a significant increase in the clotting time for PT and aPTT as well as an increase in lag time (as measured by thrombin generation) in neonates when compared with adults. In-vivo studies are required to confirm the consistency of dose-response in neonates.

Anti-Factor Xa Assay Is a Superior Correlate of Heparin Dose Than Activated Partial Thromboplastin Time or Activated Clotting Time in Pediatric Extracorporeal Membrane Oxygenation*

To assess the utility of activated clotting time, activated partial thromboplastin time, and anti-Factor Xa assay for the monitoring and dosing of heparin in pediatric patients requiring support with extracorporeal membrane oxygenation. Retrospective chart review. PICU in a single, tertiary care, academic children's hospital. Seventeen patients (age 1 d to 13.9 yr, median 0.83 yr) managed on pulmonary and cardiac extracorporeal membrane oxygenation between March 2010 and August 2012 by a single surgeon. None. Twice daily measurements of anti-Factor Xa assay, activated clotting time, and activated partial thromboplastin time were determined from the same blood specimen. Data were analyzed using SAS system v9.2. Fourteen patients (82.4%) were successfully weaned from extracorporeal membrane oxygenation and 12 (70.6%) were discharged from the hospital. Pearson correlations were used to compare heparin dose and activated clotting time, activated partial thromboplastin time, and anti-Factor Xa assay. Analysis showed negative Pearson correlations in 11 of 17 patients between the activated clotting time and heparin, as compared with seven of 17 for activated partial thromboplastin time and only one for heparin and anti-Factor Xa assay. Only four patients had moderate to strong positive correlations between activated clotting time and heparin as compared with a moderate to strong positive correlation in 10 patients for anti-Factor Xa assay and heparin. The anti-Factor Xa assay correlated better with heparin dosing than activated clotting time or activated partial thromboplastin time. Activated clotting time has a poor correlation to heparin doses commonly associated with extracorporeal membrane oxygenation. In pediatric extracorporeal membrane oxygenation, anti-Factor Xa assay may be a more valuable monitor of heparin administration.

Performance of coagulation tests in patients on therapeutic doses of rivaroxaban

Knowledge of anticoagulation status during rivaroxaban therapy is desirable in certain clinical situations. It was the study objective to determine coagulation tests most useful for assessing rivaroxaban's anticoagulant effect. Peak and trough blood samples from 29 patients taking rivaroxaban 20 mg daily were collected. Mass spectrometry and various coagulation assays were performed. "On-therapy range" was defined as the rivaroxaban concentrations determined by LC-MS/MS. A "misprediction percentage" was calculated based on how often results of each coagulation assay were in the normal reference range, while the rivaroxaban concentration was in the "on-therapy" range. The on-therapy range was 8.9-660 ng/ml. The misprediction percentages for prothrombin time (PT) and activated partial thromboplastin time (aPTT), using multiple reagents and coagulometers, ranged from 10%-52% and 31%-59%, respectively. PT, aPTT and activated clotting time (ACT) were insensitive to trough rivaroxaban: 59%, 62%, and 80% of samples had a normal result, respectively. Over 95% of PT and ACT values were elevated at peak. Four different rivaroxaban calibrated anti-Xa assays had R² values >0.98, demonstrating strong correlations with rivaroxaban drug levels. In conclusion, PT, aPTT and ACT are often normal in patients on therapeutic doses of rivaroxaban. However, PT and ACT may have clinical utility at higher drug plasma levels. Rivaroxaban calibrated anti-factor Xa assays can accurately identify low and high on-therapy rivaroxaban drug levels and, therefore, have superior utility in all clinical situations where assessment of anticoagulation status may be beneficial.

Progressive chromogenic anti-factor Xa assay and its use in the classification of antithrombin deficiencies.

Antithrombin (AT) is a slow-acting progressive inhibitor of activated clotting factors, particularly thrombin and activated factor X (FXa). However, the presence of heparin or heparan sulfate accelerates its effect by several magnitudes. AT deficiency, a severe thrombophilia, is classified as type I (quantitative) and type II (qualitative) deficiency. In the latter case mutations may influence the reactive site, the heparin binding-site (HBS) and exert pleiotropic effect. Heterozygous type II-HBS deficiency is a less severe thrombophilia than other heterozygous subtypes. However, as opposed to other subtypes, it also exists in homozygous form which represents a very high risk of venous thromboembolism. A modified anti-FXa chromogenic AT assay was developed which determines both the progressive (p) and the heparin cofactor (hc) activities, in parallel. The method was evaluated and reference intervals were established. The usefulness of the assay in detecting type II-HBS AT deficiency was tested on 78 AT deficient patients including 51 type II-HBS heterozygotes and 18 homozygotes. Both p-anti-FXa and hc-anti-FXa assays showed excellent reproducibility and were not influenced by high concentrations of triglyceride, bilirubin and hemoglobin. Reference intervals for p-anti-FXa and hc-anti-FXa AT activities were 84%-117% and 81%-117%, respectively. Type II-HBS deficient patients demonstrated low (heterozygotes) or very low (homozygotes) hc-anti-FXa activity with normal or slightly decreased p-anti-FXa activity. The p/hc ratio clearly distinguished wild type controls, type II-HBS heterozygotes and homozygotes. Concomitant determination of p-anti-FXa and hc-anti-FXa activities provides a reliable, clinically important diagnosis of type II-HBS AT deficiency and distinguishes between homozygotes and heterozygotes.

Fondaparinux in an Obese Child with Heparin-Induced Thrombocytopenia and a History of Renal Failure

A 9-year-old obese child with a history of ulcerative colitis was admitted to the intensive care unit for significant blood loss, hemorrhagic shock, and acute renal failure. Following complications from total colectomy secondary to multiple perforations, the patient developed heparin-induced thrombocytopenia (HIT) and subsequent portal vein thrombosis. Subcutaneous (SQ) fondaparinux therapy was initiated because the patient was unable to transition to oral anticoagulation. An anti-factor Xa assay was developed and used to adjust his fondaparinux therapy. Based on hemorrhagic complications and fondaparinux-based anti-factor Xa assay results, the fondaparinux was adjusted to a final dosage of 4.5 mg (0.066 mg/kg) SQ daily. In children unable to transition to oral anticoagulation, fondaparinux may be an alternative for the treatment of thrombosis associated with HIT. We noted that our patient required a lower dose per kilogram of fondaparinux than described in previous published reports. Despite this lower dosage per kilogram, our patient developed bleeding despite dosage reductions; subsequently, a few doses were held. It is unclear if this was related to his obesity, history of renal failure, or a combination of factors. Future studies should determine the optimal dose for special populations of children (e.g., those with obesity and renal failure). Until then, clinicians should routinely monitor and titrate fondaparinux therapy, ideally using a fondaparinux-specific anti-factor Xa assay.

Gerinnungsmonitoring der direkten oralen Antikoagulanzien

The introduction of the new oral direct anticoagulants dabigatran, rivaroxaban and apixaban within the past few years has changed clinical practice as these drugs do not need routine laboratory testing compared to the traditional vitamin K antagonists. However, in specific clinical situations such as invasive emergency procedures, severe haemorrhage or deteriorating renal function measurement of the anticoagulatory effect may be required. The effects of the intake of an oral direct inhibitor on readily available qualitative laboratory tests such as prothrombin time (PT), activated partial thromboplastin time (aPPT) and thrombin time (TT) depend on which oral direct inhibitor the patient has taken, the dose and the time the drug was last taken and the sensitivity of the test reagents. A quantitative determination of the Xa-inhibitors rivaroxaban and apixaban plasma concentration is possible using a specifically calibrated anti-factor Xa assay. The diluted thrombin time test (Hemoclot) is useful for measuring the plasma concentration of the thrombin inhibitor dabigatran. When interpreting global coagulation tests of patients on direct oral inhibitors one should be aware that these new anticoagulants can affect screening and diagnostic clotting tests.

Case Scenario: Management of Trauma-induced Coagulopathy in a Severe Blunt Trauma Patient

Case Scenario: Management of Trauma-induced Coagulopathy in a Severe Blunt Trauma Patient

Ion exchange chromatographic separation and isolation of oligosaccharides of intact low-molecular-weight heparin for the determination of their anticoagulant and anti-inflammatory properties

It is well known that enoxaparin, a widely used anticoagulant and low-molecular-weight heparin containing a large number of oligosaccharides, possesses anti-inflammatory activity. Whilst enoxaparin has shown promising results in various inflammatory disorders, some of its oligosaccharides have anti-inflammatory properties and others increase the risk of bleeding due to their anticoagulant effects. The aim of this study was to develop an effective ion exchange chromatographic (IC) technique which allows the separation, isolation and, consequently, the identification of different oligosaccharides of enoxaparin with or without anticoagulant activity. The developed method utilises a semi-preparative CarboPac PA100 (9 × 250mm) ion exchange column with sodium chloride gradient elution and UV detection at 232nm. The method successfully resolved enoxaparin into more than 30 different peaks. IC-derived oligosaccharides with high, moderate, low or no anticoagulant activity were identified using an anti-factor Xa assay. The anti-inflammatory activity of selected oligosaccharides was investigated using the Griess assay. Using this technique, the oligosaccharides of enoxaparin with low or no anticoagulant activity, whilst exhibiting significant anti-inflammatory activity, could be fractionated. This technique can provide a platform to identify the oligosaccharides which are devoid of significant anticoagulant activity and are responsible for the therapeutic effects of enoxaparin that have been observed in various inflammatory conditions.