Understanding of developmental haemostasis is critical to ensure optimal prevention, diagnosis, and treatment of haemorrhagic and thrombotic diseases in children. As coagulation test results are known to be dependent on the reagents/analysers used, it is recommended for each laboratory to define the age-dependent reference ranges by using its own technical condition. That study was carried out in seven centers to establish age-specific reference ranges using the same reagents and analyser. Plasma samples were obtained from 1437 paediatric patients from the following age groups: 15 days-4 weeks (n=36), 1-5 months (n=320), 6-12 months (n=176), 1-5 years (n=507), 6-10 years (n=132) and 11-17 years (n=262). Indication of coagulation testing was pre-operative screening for non-acute diseases in most cases. PT values were similar in the different age groups to those in adults, whereas longer aPTTs were demonstrated in the younger children. Plasma levels of all clotting factors, except for FV, were significantly decreased (p<0.0001) in the youngest children, adult values being usually reached before the end of the first year. The same applied to antithrombin, protein C/S, and plasminogen. In contrast, FVIII and VWF levels were elevated in the youngest children and returned to adult values within six months. The same applied to D-dimer levels, which were found elevated, particularly until six months of life, until puberty. These data suggest that most coagulation test results are highly dependent on age, mainly during the first year of life, and that age-specific reference ranges must be used to ensure proper evaluation of coagulation in children.

Introduction: One of the main advantages of using anti-Xa instead of activated partial thromboplastin time in monitoring of unfractionated heparin (UFH) therapy relies on its hypothesized standardization, with a unique therapeutic range defined to be 0.30 to 0.70 IU/mL. The aim of the present study was to compare the inter-reagent agreement of anti-Xa activity. Methods: Citrate tubes were obtained from 104 inpatients on UFH. Plasma samples were stored frozen in aliquots at −70°C before being shipped to three accredited coagulation laboratories to be evaluated for anti-Xa activity using their routine assay(s). Pooled normal plasmas spiked with dilutions of the 6th International Standard of UFH to achieve anti-Xa activities up to 1.0 IU/mL were evaluated using the same techniques. Results: In the plasmas from patients on UFH, the median anti-Xa activity ranged from 0.37 IU/mL with one reagent to 0.57 IU/mL with another; results were in between (0.45 IU/mL) using two other reagents. Comparisons of results obtained using the different reagents demonstrated unacceptable bias up to 0.24 IU/mL between some reagents (41% difference). The concordance as whether anti-Xa activities measured using different reagents were within or outside the therapeutic range was between 0.411 and 0.939 (kappa). Similar discrepancy was demonstrated for anti-Xa activities when evaluating normal plasma spiked with the International Standard. A discrepancy of the same order of magnitude was demonstrated in the 2017 External Quality Assessment Program provided by the External Quality Control in Assays and Tests exercises. Conclusions: The reported discrepancy between test results obtained using different anti-Xa assays clearly suggests a lack of standardization of that assay with potentially significant impact on the patients' anticoagulation.

Introduction: Unfractionated heparin (UFH) therapy is monitored by using the anti-activated factor X (anti-Xa) activity, or the activated partial thromboplastin time (APTT), which remains the most widely used assay. One of the main advantages of anti-Xa relies on its hypothesized standardization, with a unique therapeutic range (0.30-0.70 IU/ml) for all reagents, whereas APTT is influenced by numerous preanalytical and analytical parameters not related to the anticoagulant activity of UFH. Methods:The aim of this study was to compare the anti-Xa-correlated APTT therapeutic ranges calculated using different combinations of APTT (n = 4) and anti-Xa reagents (n = 4) in frozen citrated plasmas from 87 inpatients on UFH. Results:The median APTT ratio ranged from 2.19 for the less sensitive to 3.23 for the most sensitive reagent, whereas the median anti-Xa activity was between 0.37 IU/ml and 0.57 IU/ml. The APTT therapeutic ranges calculated to correlate with anti-Xa activities between 0.30 and 0.70 IU/ml were found to be highly different from one combination of APTT reagent and analyzer to another. The same applied to the therapeutic range of a single APTT reagent calculated using different anti-Xa assays performed on the same analyzer, leading to a lack of agreement as to whether a sample was classified as subtherapeutic, therapeutic or supratherapeutic in 8.0% to 23.0% of the patients, with kappa coefficients between 0.908 and 0.753. Conclusions:These results suggest that the APTT therapeutic range calculated to correlate with anti-Xa activities between 0.30 and 0.70 IU/ml is influenced not only by the APTT reagent, but also by the anti-Xa reagent used for calculation.

Background: As aging was found to be associated with increased D-dimer levels, the question arose whether D-dimer measurement was useful in the diagnostic strategy of venous thromboembolism (VTE) in elderly patients. Aim of the study:To compare retrospectively the performance of six diagnostic strategies based on the three-level Wells scores and various cut-off levels for D-dimer, evaluated using the HemosIL D-Dimer HS 500 assay, in a derivation cohort of 644 outpatients with non-high pretest probability (PTP) of VTE. The clinical usefulness of the best-performing strategy was then confirmed in a multicenter validation study involving 1255 consecutive outpatients with non-high PTP. Results:The diagnostic strategy based on the age-adjusted cut-off level calculated by multiplying the patient's age by 10 above 50 years was found to perform the best in the derivation study with a better sensitivity-to-specificity ratio than the conventional strategy based on the fixed cut-off level (500 ng/ml), a higher specificity and a negative predictive value (NPV) above 99%. Such an increase in test specificity was confirmed in the validation cohort, with the NPV remaining above 99%. Taking into account the local reimbursement rates of diagnostic tests, using this strategy led to a 6.9% reduction of diagnostic costs for pulmonary embolism and a 5.1% reduction for deep vein thrombosis, as imaging tests would be avoided in a higher percentage of patients. Conclusion:The diagnostic strategy of VTE based on the age-adjusted cut-off level for D-dimer in patients over 50 years was found to be safe, with NPV above 99%, and cost-effective.

Background D-dimer levels below a well-defined cut-off level enable to safely rule out VTE in patients with a low or intermediate pre-test probability (PTP), as the test negative predictive value (NPV) was high. As ageing is associated with increased D-dimer levels, the question was raised of the usefulness of their measurement to rule out VTE in elderly patients. Various attempts were made in the recent years to address that issue, particularly the use of age-adjusted cut-off values calculated by multiplying the patient's age by 10, in patients aged over 50. Aim of that study The aim of the study was to validate such a strategy, and to evaluate its economic impact in unselected outpatients referred to the emergency departments of 5 French centres (2 university hospitals, and 3 general hospitals). Patients, Materials and Methods After exclusion of those on anticoagulant treatment at the time of the diagnosis (n=23), a total of 1255 consecutive patients with a non-high PTP of VTE were included in the study. The same standardized procedure was used in the 5 centres, i.e. D-dimer measurement in patients with a non-high PTP, and imaging techniques (usually computed pulmonary angiography in case of suspected PE and Doppler ultrasonography in case of suspected DVT) only when D-dimer was above the cut-off level. D-dimer was evaluated using the same latex-based fully automated assay (HemosIL D-dimer HS500 assay, Instrumentation Laboratory). Test results were expressed in ng/mL fibrinogen equivalent units (FEU), and the traditional cut-off level for VTE exclusion was 500 ng/mL. Results VTE was diagnosed in 105 patients of the 1255 included patients (8.4%): 88 patients were diagnosed out of the 1082 patients referred for suspected PE and 27 out the 173 referred for suspected DVT. D-dimer levels were above 500 ng/mL in all patients with VTE and in 521 of the 1150 patients without VTE (45.3%). The test NPV was 100% as well as its sensitivity. If the overall test specificity was 54.7%, it significantly decreased in an age-dependent manner over 70 years, related to a high percentage of increased D-dimer levels in elderly patients, particularly in those above 80 years. Using age-adjusted cut-off levels, calculated by multiplying the patient's age by 10, induced a significantly improvement in test specificity, particularly in very old patients with an overall NPV=60.2% vs. 54.7% using the fixed cut-off value. The overall NPV remained high (99.9%), even if a 78 y-old female with a low PTP of PE would have been misdiagnosed as her D-dimer level (540 ng/mL) was above 500 ng/mL but below the age-adjusted cut-off value. Such an improvement in test performance was found both in patients with suspected PE and DVT (Table). As this increase in test specificity would have led to exclude VTE in a higher percentage of patients in the studied population, we evaluated the cost-effectiveness of that strategy, taking into account the local cost of D-dimer testing, angiography and Doppler US (16.20, 58.72, and 75.60 Euros respectively). In the case of suspected PE, the economic impact of the proposed diagnosis strategy was a decreased of 6.9% of total costs (45,023.4 vs. 48,356.4 Euros). In the case of DVT, the overall saving was 5.1% (9,909 vs. 10,438.2 Euros). If such an analysis was used in the US, where angiography and Doppler US were more expensive (648 and 226 US$ respectively), and D-dimer less costly (14 US$), the cost savings would have been even higher (-11.0% for PE, and -6.3% for DVT). Conclusions The use age-adjusted cut-off levels for D-dimer, in patients aged over 50 years old, leaded to a significant increase in the test specificity, but correlatively to slightly decreased NPV and sensitivity, as some patients with D-dimer levels above 500 ng/mL but below the age-adjusted cut-off value could be misdiagnosed. However such a strategy was found to be safe in our studied populations, as the NPV remained high (99.9%), and cost-effective. Table Table. Disclosures No relevant conflicts of interest to declare.