Summarymedium may produce false positive results (11). In this report, we describe two modifications of the original Bethesda assay which result Antibodies against factor VIII coagulant activity can appear in in markedly increased specificity and allowed us to diagnose and monihaemophiliacs who are treated with factor VIII preparations but also tor the presence of factor VIII :C inhibitors, spontaneously in non-haemophiliacs. The Bethesda assay is the most commonly used method to detect these antibodies, but it lacks specificity especially in the lower range resulting in unreliable data.Two modifications are proposed and tested to resolve the imper fections: 1. Buffering the normal plasma used in the assay-and control mixture with 0.1 M imidazole to pH 7.4. p 2. Replacing the imidazole buffer in the control mixture by immunodepleted factor VIII deficient plasma. These modifications allow better discrimination between positive and negative samples and improve reliability.

Electrowetting-on-dielectric (EWOD) lab-on-a-chip systems have already proven their potential within a broad range of bio-assays. Nevertheless, research on the analytical performance of those systems is limited, yet crucial for a further breakthrough in the diagnostic field. Therefore, this paper presents the intrinsic possibilities of an EWOD lab-on-a-chip as a versatile platform for homogeneous and heterogeneous bio-assays with high analytical performance. Both droplet dispensing and splitting cause variations in droplet size, thereby directly influencing the assay's performance. The extent to which they influence the performance is assessed by a theoretical sensitivity analysis, which allows the definition of a basic framework for the reduction of droplet size variability. Taking advantage of the optimized droplet manipulations, both homogeneous and heterogeneous bio-assays are implemented in the EWOD lab-on-a-chip to demonstrate the analytical capabilities and versatility of the device. A fully on-chip enzymatic assay is realized with high analytical performance. It demonstrates the promising capabilities of an EWOD lab-on-a-chip in food-related and medical applications, such as nutritional and blood analyses. Further, a magnetic bio-assay for IgE detection using superparamagnetic nanoparticles is presented whereby the nanoparticles are used as solid carriers during the bio-assay. Crucial elements are the precise manipulation of the superparamagnetic nanoparticles with respect to dispensing and separation. Although the principle of using nano-carriers is demonstrated for protein detection, it can be easily extended to a broader range of bio-related applications like DNA sensing. In heterogeneous bio-assays the chip surface is actively involved during the execution of the bio-assay. Through immobilization of specific biological compounds like DNA, proteins and cells a reactive chip surface is realized, which enhances the bio-assay performance. To demonstrate this potential, on-chip adhesion islands are fabricated to immobilize MCF-7 human breast cancer cells. Viability studies are performed to assess the functionalization efficiency.

The detection and quantification of factor VIII (FVIII) inhibitors is clinically important both for the identification of hemophilia A patients with inhibitors and for the management of immune tolerance treatment. Only limited data are available on the between-laboratory variation of FVIII inhibitor testing. This report describes the evaluation of the results of the large-scale external quality assessment program of the European Concerted Action on Thrombosis Foundation. This study includes the results of six different surveys for the period 2006 to 2008 with 100 to 170 participating laboratories. The overall between-laboratory variation ranged from 28% to 52% with a slightly lower variation for the Nijmegen assay (approximately 39%) on average than for the Bethesda assay (approximately 45%). The use of buffered normal pooled plasma as FVIII source showed better performance compared with the use of nonbuffered pooled plasma; likewise the use of FVIII-deficient plasma compared with the use of imidazole buffer. However, the combination of both was essential for lowest between-laboratory variation. The Nijmegen assay also showed better performance with respect to specificity and sensitivity than the Bethesda assay, although the results for neither were entirely satisfactory. In general, it can be concluded that the measurement of FVIII inhibitory antibodies with the Nijmegen assay should be favored over the use of the Bethesda assay. However, further improvement of the laboratory test for FVIII inhibitors is urgently needed.

Thrombin and plasmin are the key enzymes involved in coagulation and fibrinolysis. A novel hemostasis assay (NHA) was developed to measure thrombin and plasmin generation in a single well by a fluorimeter. The NHA uses two fluorescent substrates with non-interfering fluorescent excitation and emission spectra. The assay was tested in vitro using modulators like heparin, hirudin, epsilon-aminocaproic acid, gly-pro-arg-pro peptide and reptilase and validated by measurement of prothrombin fragment 1+2 and plasmin-alpha2-antiplasmin levels. Intra- and inter-assay coefficients of variation were < 9% and 6-25%, respectively. Interplay between coagulation and fibrinolysis was demonstrated by the effect of tissue-type plasminogen activator on thrombin generation and by the different responses of activated protein C and thrombomodulin on fibrinolysis. The last responses showed the linkage between coagulation and fibrinolysis by thrombin activatable fibrinolysis inhibitor. In conclusion, this strategy allows detection of coagulation, fibrinolysis and their interplay in a single assay.

No abstract

Summary Thrombocytopenia develops early in malaria, but the underlying mechanisms remain incompletely understood. We studied the aetiology of malaria‐associated thrombocytopenia in volunteers experimentally infected with Plasmodium falciparum malaria, in Indonesian malaria patients and in ex vivo studies. In experimental human malaria, the decrease in platelet counts was associated with a concurrent rise in young platelets (immature platelet fraction) and thrombopoietin. D‐dimer concentrations were moderately elevated without a prolongation in the activated partial thromboplastin time or decrease in fibrinogen. There was no increase in expression of the platelet surface markers CD62P, PAC‐1 and CD63 and in plasma concentrations of the platelet factors P‐selectin, CXCR4, CXCL7, RANTES and CD40L. In contrast, concentrations of soluble glycoprotein‐1b (sGP1b), the external domain of the platelet receptor for von Willebrand factor (VWF), increased early. Indonesian malaria patients also had elevated concentrations of sGP1b, which correlated with VWF concentrations. Finally, incubation of platelets with parasitized erythrocytes in vitro failed to induce platelet aggregation or activation. We concluded that neither compromised platelet production nor platelet activation or consumptive coagulopathy were responsible for the early thrombocytopenia in malaria. We hypothesize that the increase in sGP1b concentrations results from VWF‐mediated GP1b shedding; a process that may prevent excessive adhesion of platelets and parasitized erythrocytes.

All methods for the detection of factor VIII (FVIII) inhibitors are based on the measurement of inactivation of FVIII in a mixture of the test plasma containing the putative inhibitor and an exogenous source of FVIII. Various types of assays have been developed since the first inhibitor was described in 1941. Nowadays, two methods are preferably used, the Bethesda assay and the Nijmegen assay. Although the Nijmegen assay shows a better specificity and intra- and interlaboratory variation, it is still hampered by several limitations related to assay characteristics (pH, temperature, and time of incubation), type of control sample, and the von Willebrand factor content of the assay mixture. Epitope specificity plays an important role in the reliability of functional assays because inhibitors against the C2 domain are more difficult to quantify compared with inhibitors against the A2 domain. Finally, lupus anticoagulants can interfere with inhibitor assays, resulting in aberrant results. This report describes in detail the various problems encountered with the assays used in the quantification of functional FVIII inhibitors.

A randomised clinical trial was conducted to establish the effects of oral and intramuscular administration of vitamin K at birth on plasma concentrations ofvitamin K1, proteins induced by vitamin K absence (PIVKA-II), and clotting factors. Two groups of about 165 healthy breast fed infants who received at random 1 mg vitamin K1 orally or intramuscularly after birth were studied at 2 weeks and 1 and 3 months of age. Although vitamin K1 concentrations were statistically significantly higher in the intramuscular group, blood coagulability, activities of factors VII and X and PIVKA-II concentrations did not reveal any difference between the two groups. At 2 weeks of age vitamin K, concentrations were raised compared with reported unsupplemented concentrations and no PIVKA-II was detectable. At 3 months vitamin K1 concentrations were back at unsupplemented values and PIVKA-II was detectable in 11.5% of infants. Therefore, a repeated oral prophylaxis will be necessary to completely prevent (biochemical) vitamin K deficiency beyond the age of 1 month.