Guidelines on preparation, certification, and use of certified plasmas for ISI calibration and INR determination.

Reliable international normalized ratio (INR) determination depends on accurate values for international sensitivity index (ISI) and mean normal prothrombin time (MNPT). Local ISI calibration can be performed to obtain reliable INR. Alternatively, the laboratory may determine INR directly from a line relating local log(prothrombin time [PT]) to log(INR). This can be done by means of lyophilized or frozen plasmas to which certified values of PT or INR have been assigned. Currently there is one procedure for local calibration with certified plasmas which is a modification of the WHO method of ISI determination. In the other procedure, named 'direct' INR determination, certified plasmas are used to calculate a line relating log(PT) to log(INR). The number of certified plasmas for each procedure depends on the method of preparation and type of plasma. Lyophilization of plasma may induce variable effects on the INR, the magnitude of which depends on the type of thromboplastin used. Consequently, the manufacturer or supplier of certified plasmas must assign the values for different (reference) thromboplastins and validate the procedure for reliable ISI calibration or 'direct' INR determination. Certification of plasmas should be performed by at least three laboratories. Multiple values should be assigned if the differences between thromboplastin systems are greater than 10%. Testing of certified plasmas for ISI calibration may be performed in quadruplicate in the same working session. It is recommended to repeat the measurements on three sessions or days to control day-to-day variation. Testing of certified plasmas for 'direct' INR determination should be performed in at least three sessions or days. Correlation lines for ISI calibration and for 'direct' INR determination should be calculated by means of orthogonal regression. Quality assessment of the INR with certified plasmas should be performed regularly and should be repeated whenever there is a change in reagent batch or in instrument. Discrepant results obtained by users of certified plasmas should be reported to manufacturers or suppliers.

Field study of lyophilized calibrant plasmas for fresh plasma INR determination.

An alternative approach to INR estimation is for laboratories to calibrate their own local system using calibrant plasmas supplied by manufacturers or reference laboratories. The purpose of the present study was to investigate the within-laboratory variability of a calibrant plasma procedure using various sets of lyophilized plasmas. INR had been assigned to 13 calibrant plasmas in a previous multi-center study. Each of 10 other ("field") laboratories measured PTs in the 13 calibrant plasmas and in 15 local fresh coumarin plasmas, using three different thromboplastin reagents. Each fresh coumarin PT was converted to INR using a calibration procedure with a set of 4 calibrants (1 normal + 3 abnormals). The abnormals of each set were either coumarin or artificial and were used with different assigned INR. When the INR had been assigned with a thromboplastin brand identical to the thromboplastin in the field laboratory, the procedure was named "reagent-specific" calibration. Otherwise the procedure was named "dissimilar" calibration. Using "reagent-specific" calibration procedures, relatively homogeneous INR were obtained for the fresh coumarin plasmas, whatever type of calibrant was used. In contrast, discrepant INR were obtained when "dissimilar" cross-species calibration procedures were used. The study was limited to 9 laboratories using the same type of coagulometer and one using a different type.

Preliminary evaluation of two new rapid immunoturbidimetric D-dimer assays in patients with clinically suspected venous thromboembolism (VTE).

The practical utility and diagnostic accuracy of two new rapid, automated and quantitative immunoturbidimetric D-dimer methods have been evaluated in a population of 123 randomly selected patients with suspected VTE. The STA Liatest D-dimer and MDA D-dimer methods are based on the photo-optical measurement of the rate of agglutination of antibody-coated latex particles. The VIDAS D-dimer automated Elisa was used as the reference method. Diagnosis was confirmed in 51 patients (29 PE, 19 DVT, 3 DVT+PE). The immunoturbidimetric methods compared favorably with the VIDAS Elisa as judged from the correlation coefficients of linear regression lines (r = 0.82, MDA vs VIDAS; r = 0.75, STA vs VIDAS) and areas under the curve of ROC plots (VIDAS 0.83; STA 0.83; MDA 0.81). At a discriminant value of 500 ng/mL, all three D-dimer assays showed high sensitivity (96-98%), high NPV (93-97%) and moderate specificity (39-42%). Reproducibility of results around the cut-off is an important aspect of the diagnostic utility of D-dimer assays. CV's of duplicate determinations in this critical zone showed average values of 5.4% and 17.0% for MDA and STA, respectively. These data demonstrate that such rapid and automated latex-based methods for the quantitative measurement of D-dimer hold promise as reliable and cost-efficient approaches for the exclusion of VTE. Prospective patient management studies will be required to confirm this.

Molecular bases of antithrombin deficiency in French families: identification of seven novel mutations in the antithrombin gene.

We have investigated the molecular bases of familial antithrombin deficiency in eight French families. Eight mutations in the antithrombin coding exons were identified, seven of which were novel mutations. In all cases, individuals were heterozygous for the mutation. We found two small frameshift deletions in exon 3a, leading to type I deficiency. Five missense mutations in exons 3b or 5 also caused type I deficiency and their potential consequences on the antithrombin three-dimensional structure were analysed. The last mutation in exon 4 was associated with a type II 'reactive site' deficiency: a dysfunctional antithrombin that is affected in its interaction with thrombin was present in circulation.

[Interest in variations in soluble ICAM-1 plasma levels. From physiology to clinical applications]. / Intérêt des variations plasmatiques d'ICAM-1 soluble. De la physiologie à l'application clinique.

Intracellular adhesion molecule 1 (ICAM-1) is an adhesion-related molecule belonging to the immunoglobulin superfamily. This molecule is found on the cell membrane of endothelial cells. When activated ICAM-1 allows stable leukocyte adhesion to the endothelial surface. ICAM-1 is found not only in the membrane form but also circulating in serum. ICAM-1 (extracellular part of ICAM-1). This enables ICAM-1s to bind leukocyte integrin receptors such as LFA-1 (CDI1a/CD18) and Mac-1 (CDI1b/CD18) and therefore provide adaptive changes in the adhesion process between circulating cells and the endothelium.

Multicenter evaluation of lyophilized and deep-frozen plasmas for assignment of the International Normalized Ratio.

The interlaboratory variation of the International Normalized Ratio (INR) in various external quality assessment schemes is still relatively high. This is partly caused by inaccuracy of manufacturers' stated International Sensitivity Index (ISI) and/or local instrumentation effects. The interlaboratory variation and accuracy of INR determinations may be improved by a local calibration procedure based on lyophilized plasmas with assigned INRs. The purpose of the present study was to determine INR values for different types of lyophilized plasmas to be used for local calibration. A total of 13 lyophilized plasmas (one normal, six from coumarin-treated patients, six artificially depleted) were analyzed by 10 laboratories, each using five calibrated prothrombin time (PT) systems. INRs were calculated for each plasma using each laboratory's specific ISI and mean normal prothrombin time values. In the same way, five deep-frozen pooled plasmas from coumarin-treated patients were analyzed. There were significant INR differences for the lyophilized plasmas between the prothrombin time systems. The differences were relatively small for the deep-frozen coumarin plasmas (CV 2.6-3.3%) and three lyophilized coumarin plasmas from one manufacturer (CV 3.7-4.8%). Important INR differences were observed for three lyophilized coumarin plasmas from another manufacturer (CV 9.5-14.1%) and several artificially depleted plasmas (CV 5.3-12.8%). The citrate concentrations in the artificially depleted plasmas were lower than those in the normal and coumarin plasmas. These differences should be considered in the selection and certification of plasmas as calibrants for local calibration of PT systems. The lyophilized plasmas' INR values obtained in the present study will be used for a field study of local PT calibration to assess their efficacy.