Chromogenix Coamatic® Factor VIII is a chromogenic assay kit for the photometric determination of factor VIII activity in plasma, such as when identifying factor VIII deficiency or monitoring patients on replacement therapy as well as for potency estimation of FVIII concentrates. This Factor VIII test kit fulfills the requirements of the European Pharmacopoeia for factor VIII concentrate testing. Co-lyophilization of reagents for convenient handling. Reliable tool for hemophilia classification. No interference from heparin levels up to 1.5 IU/ml. The Factor VIII kit has two measuring ranges.
|FIXa, Ca2+, phospholipid
|Peptide + pNA
In the presence of calcium ions and phospholipids, factor X is activated to factor Xa by factor IXa. This activation is greatly stimulated by factor VIII which acts as a cofactor in this reaction. By using optimal amounts of Ca2+, phospholipid and factor IXa, and an excess of factor X, the rate of activation of factor X is linearly related to the amount of factor VIII. Factor Xa hydrolyses the chromogenic substrate S-2765™ thus liberating the chromophoric group, pNA. The colour is then read photometrically at 405 nm. The generated factor Xa and thus the intensity of colour is proportional to the factor VIII activity in the sample. Hydrolysis of S-2765™ by thrombin formed is prevented by the addition of the synthetic thrombin inhibitor I-2581 together with the substrate.
PRECISE. SENSITIVE. ACCURATE. Coamatic® Factor VIII for better hemophilia testing.
The Chromogenix Coamatic® Factor VIII assay kit provides reagents and chromogenic methods for determining factor VIII activity in human plasma and in factor VIII concentrates. Factor VIII is a high molecular weight plasma protein which serves as a cofactor to factor IXa in its activation of factor X to Xa. Deficiency of factor VIII causes a severe bleeding disorder, hemophilia A. The severity of this bleeding disorder is inversely related to the factor VIII concentration. Hemophilia A patients are generally classified according to their factor VIII activity into three categories: <0.01 IU/mL = severe, 0.01-0.04 IU/mL =moderate and 0.05-0.25 IU/mL = mild hemophilia.
|What is the Chromogenix Coamatic® Factor VIII measurement principle?
|What is the function of von Willebrand Factor? Briefly describe von Willebrand disease.
|von Willebrand factor (vWf) is a glue-like adhesive protein that is responsible for the adhesion of platelets to damaged vascular endothelium. It also carries and protects factor VIII. von Willebrand disease is a hereditary bleeding disorder caused by moderate-to-severe factor VIII deficiency and low-levels of factor VIII-related antigen (substances necessary for blood clotting). Additionally, there is insufficient von Willebrand factor which also helps blood clot. The von Willebrand factor helps platelets to stick to the blood vessel wall and to each other, which is necessary for normal blood clotting.
Visit the vWF product pages for available kits to measure vWF antigen, activity, and collagen binding.
|We know that low levels of factor VIII activity constitutes hemophilia A, but are there any clinical manifestations of elevated factor VIII levels? How can a researcher measure elevated FVIII levels?
|There is evidence that a high level of factor VIII is a risk factor for venous thrombosis. There are two articles in Thrombosis and Haemostasis 2000; volume 83:
1.Kraaijenhagen et al. High plasma concentration of factor VIII:c is a major risk factor for venous thromboembolism (p. 5-9)
An adaptation of Chromogenix Coamatic® FVIII has been developed to allow accurate determination of elevated factor VIII levels. The method is for research use only.
|What are FVIII inhibitors, and how can I measure them?
|FVIII inhibitors appear in about 25% of severe hemophilia A patients. They are most common in patients with inversions, large deletions and nonsense mutations. Inhibitor titer varies 1000-fold; high titer seriously impairs treatment efficacy. Inhibitors can be transient or persistent. and appear irrespective of which FVIII concentrate is selected. High titer patients are treated with high doses of human or porcine concentrate. View the FVIII product pages for kits and assays for FVIII Inhibitor measurements.
|Sometimes when I run the Chromogenix Coamatic® FVIII assay, I see an upward drift in my activity from the first to the last samples. Why is this?
|Thrombin, 1 NIH unit, is included in the factor reagent. It has been shown that thrombin can activate FX, and over time you will see an increase of up to 5% activity. If you are doing numerous samples at once on an automated instrument, you might want to consider Coatest® FVIII.
|Is it OK to use glass tubes for the Chromogenix Factor VIII assay?
|No, glass surfaces may interfere with the generation of FXa. Use plastic tubes for the manual method.
|If thrombin is formed, will it hydrolyze the substrate S-2765™ when using Chromogenix Coamatic®, Coatest® SP, or Coatest® SP4 FVIII kits?
|No, hydrolysis of S-2765™ by thrombin is prevented by the addition of the synthetic thrombin inhibitor I-2581.
|Who can benefit from using chromogenic factor VIII assays?
|Clinicians or researchers interested in determining FVIII levels in patients with hemophilia A or with elevated factor VIII levels, which may be associated with thrombotic risk. Also, manufacturers interested in determining factor VIII potencies. The chromogenic FVIII activity method has been selected as the reference method by the EP for potency estimation of VIII concentrates, and it is a valuable tool for diagnosis an monitoring of hemophilia and for thrombophilia screening.
|What is the advantage of using the Chromogenix Coamatic® FVIII over a clotting test?
|While clotting assays are cheap, rapid, and simple to perform, they are sensitive to pre-activation, show interferences in the assays, and can give overestimation of FVIII concentrates. They also require a considerable amount of FVIII deficient plasma.
Coamatic® FVIII is also rapid and simple, and has additional benefits. It is suited for a wide range of automated instrument applications, there is no heparin influence, and it is highly sensitive, precise and accurate. The low measurement range provides a reliable tool for the classification of bleeders.
|What is the difference between Chromogenix Coamatic® FVIII, Coatest® SP FVIII, and Coatest® SP FVIII?
|All of these kits measure the same thing — factor VIII activity in plasma and potency estimation of FVIII concentrates. Coamatic® FVIII includes the FXa substrate S-2765™, and the factor reagent FIXa + FX and thrombin colyophilized with CaCl2 and phospholipid. The Coatest® SP FVIII includes the FXa substrate S-2765™, and the FIXa + FX reagent, CaCl2, and phospholipid are all separate components in the kit. Incubation times are a little longer, and the reagent prep is less simple. Coatest® SP4 FVIII is exactly the same as Coatest® SP FVIII, but the FIXa + FX reagent is divided into 4 vials of 1.8 U (reconstituted with 3 ml) instead of 1 vial of 6 U (reconstituted with 10 ml).
|What should I do for standards and controls for Factor VIII?
|DiaPharma has calibrators, normal and abnormal controls available. Clinicians can also use their own pooled normal plasma; however, it must be calibrated against an international standard to be sure what concentration the plasma has. If the normal plasma does not contain exactly 1 IU/ml ( which corresponds to 100%) factor VIII, the values of the standards must be recalculated in order to obtain a correct factor potency assignment. Reference plasma is available from the National Institute for Biological Standards and Controls (NBSB). The calibration should be performed by running complete standard curves on two or more independent occasions. Industrial manufacturers, in contrast, use for their standard Mega-2, which is a compilation of factor VIII concentrate.
|What is the measurement principle behind the FVIII chromogenic kits?
|First, factor VIII circulates in the plasma bound to von Willebrand factor (vWf). Thrombin cleaves and activates factor VIII and releases vWf. The vWf is then free to bind to ruptured endothelial cell surfaces where it activates platelet aggregation. The released FVIIIa acts as a cofactor of factor IXa to generate factor Xa. In the presence of Ca2+ and phospholipids, FX is activated to FXa by FIXa (look at the coagulation cascade for a better understanding). Since FVIIIa is a cofactor to FIXa, it greatly stimulates the reaction. By using optimal amounts of Ca2+, phospholipid, and FIXa, and an excess of FX, the rate of activation of FX is linearly related to the amount of FVIII. FXa hydrolyses the chromogenic substrate S-2765™ which releases the chromophoric group pNA. The color is read at 405 nm, and generated FXa and thus the intensity of color, is proportional to the FVIII activity in the sample.
|What are the latest recommendations for measuring potentcies of high purity factor VIII concentrates?
|Why is thrombin added in the Chromogenix Coamatic® FVIII factor reagent?
|Thrombin activates FX, and this happens when the reagent is reconstituted. An incubation step is required in the Chromogenix Coatest® FVIII kit.
|Protein concentrations in plasma