In vitro sensitivity of different activated partial thromboplastin time reagents to mild clotting factor deficiencies.

INTRODUCTION: Activated partial thromboplastin time (aPTT) is a routine clotting assay that is widely used to globally screen for coagulation abnormalities. It is commonly admitted that a prolonged test result, may trigger the need for specific assays to be performed, particularly factor measurement. However, the sensitivity of aPTT reagents to deficiencies of clotting factors varies. METHODS: We evaluated, according to the recommendation of the CLSI H47-A2 guideline, the responsiveness to single factor levels of five aPTT reagents by using factor-deficient plasmas spiked with a calibration plasma to produce individual factor activities ranging from <1 to ~100 Unit (U)/dL. Test results were expressed as the sample-to-control ratio, the latter was defined as the clotting time obtained in the calibration plasma containing ~100 U/dL factor activity. The factor activity producing a prolongation of aPTT above the upper limit of its specific normal range (in ratio) was assigned as the factor responsiveness in U/dL to that reagent. RESULTS: Responsiveness ranged from 34 to 47 U/dL to FVIII: C, from 18 to 57 U/dL to FIX, from 38 to 52 U/dL to FXI, from 29 to 50 U/dL to FXII, from 40 and 59 U/dL to FV, from 7.5 to 49 U/dL to FX, and from 9.1 to 10.5 U/dL to FII. CONCLUSIONS: These results suggest that the sensitivity of the tested aPTT reagents to single factor deficiency is highly variable. Moreover, for one given aPTT reagent, its sensitivity was very different depending on the deficient factor. This must be considered when analyzing clinical materials.

[Activated partial thromboplastin time prolongation in paediatrics. Retrospective monocentric study at the Nice University Hospital]. / Allongement isolé du temps de céphaline activé en pédiatrie. Étude rétrospective monocentrique au CHU de Nice.

UNLABELLED: The study of hemostasis often arises in paediatrics. Evidence of activated partial thromboplastin time (aPTT) prolongation sometime due to the presence of a circulating anticoagulant (antiphospholipid syndrome [APS]) may be embarrassing for the physician. AIM OF THE STUDY: To evaluate the prevalence of this situation, to identify the leading indicators and assess their impact. PATIENTS AND METHOD: All children aged 1 to 18 years old undergoing blood sample whatever was the reason, at the Nice University Hospital with existing isolated aPTT prolongation, were included. The assessment was completed by a mixing test, calculation of Rosner's index as well as the study of an APS and the measurement of factor VIII, IX, XI, XII. RESULTS: Between July 2006 and March 2008, 27 of 1845 children observed (1.5%) were selected for further study. Mean age was 6.17 years old. For 16 of the patients, aPTT prolongation was fortuitously discovered. Symptomatic subjects were older (9.8 vs. 5.2 years of age; P = 0.03). A significantly higher aPTT was indicative of an APS and predicted a positive Rosner Test outcome. A prolongated kaolin clotting time, observed among the younger subjects (3.45 vs. 8.88 years of age; P = 0.0011), was associated with a high aPTT prolongation (57.3 vs. 42.6s; P = 0.0009). CONCLUSION: In our study, the discovery of a prolongated aPTT is most often incidental and tends to occur during winter. The presence of a highly prolongated aPTT, abnormal kaolin clotting time and positive Rosner Test are strong predictors of the existence of an APS, especially in very young children. These antibodies are nonpathogenic and transitional.

Measurement of factor VIII activity using one-stage clotting assay: a calibration curve has not to be systematically included in each run.

Coagulation factor VIII (FVIII) is usually evaluated using activated partial thromboplastin time-based one-stage clotting assays. Guidelines for clotting factor assays indicate that a calibration curve should be included each time the assay is performed. Therefore, FVIII measurement is expensive, reagent- and time-consuming. The aim of this study was to compare FVIII activities obtained using the same fully automated assay that was calibrated once (stored calibration curve) or each time the assay was performed. Unique lots of reagents were used throughout the study. We analysed 255 frozen plasma samples from patients who were prescribed FVIII measurement including treated and untreated haemophilia A patients. Twenty-six runs were performed on a 28-week period, each including four lyophilized control and at most 10 patient plasma samples. In control samples, FVIII activities were not significantly different when the assay was performed using the stored calibration curve or was daily calibrated. The same applied to FVIII activities in patient plasma samples that were not significantly different throughout the measuring range of activities [68.3% (<1-179) vs. 67.6% (<1-177), P=0.48] and no relevant bias could be demonstrated when data were compared according to Bland and Altman. These results suggest that in the studied technical conditions, performing the FVIII assay using a stored calibration curve is reliable, for at least 6 months. Therefore, as far as the same lots of reagents are used, it is not mandatory to include a calibration curve each time the FVIII assay was performed. However, this strategy has to be validated if the assay is performed in different technical conditions.

[Type 2N von Willebrand disease (Normandy)]. / La maladie de Willebrand de type 2N "Normandie". À propos d'une observation.

Willebrand disease is the most common constitutional abnormality of hemostasis. It reflects a qualitative or quantitative abnormality of von Willebrand factor (vWF) responsible for hemorrhagic syndrome, mainly mucosal, of variable expression. Type 2N (Normandy) is a rare form of von Willebrand disease due to a qualitative abnormality of vWF that disrupts its ability to bind to factor VIII. The disease biologically combines APTT prolongation, a lower level of factor VIII, and a normal or subnormal rate of vWF, which may suggest a mild form of hemophilia A. This confusion can lead not only to a misdiagnosis but also to inappropriate treatment.

[Cerebral vascular complication of hyperhomocysteinemia. Controlling thromboembolic complications with folates]. / Accident vasculaire cérébral avec hyperhomocystéinémie. Arrêt des accidents thromboemboliques sous folates.

BACKGROUND: Young patients who experience cardiovascular events may have raised levels of homocysteine. There may be several causes for this hyperhomocysteinemia. CASE REPORT: Cerebrovascular disease occurred in a 40-year-old female smoker with hyperhomocysteinemia. This patient subsequently had several episodes of thromboembolism involving the brain and lower limb arteries. Prothrombin concentration was difficult to control with antivitamin K anticoagulants. Investigations to identify a genetic cause of hyperhomocysteinemia revealed that she was homozygous for the C677T mutation on the methylenetetrahydrofolate reductase gene. There was no G1691A mutation of the factor V gene, a risk factor for familial thrombosis. Supplementation with folic acid successfully halted episodes of thromboembolism (follow-up 2 years) and prothrombin levels stabilized under treatment. DISCUSSION: The C677T mutation, which is common in the general population (15.7%), cannot explain the effect of folate supplementation alone. Other mutations affecting homocysteine metabolism could have a potentializing effect on vascular events.