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The Diapharma Factor X Kit is an in vitro diagnostic test kit for the quantitative determination of Factor X activity in human citrated plasma. Factor X activity is useful for monitoring patients on oral anticoagulant therapy (warfarin) where baseline INR values are prolonged and INR results are not reliable, such as in OAC patients with lupus inhibitors. The DiaPharma Factor X Kit is also useful for screening for factor X deficiencies.

The Diapharma Factor X chromogenic assay kit allows labs to accurately predict therapeutic warfarin when INR values are unreliable, such as in the presence of lupus anticoagulants or when direct thrombin inhibitors are discontinued (bridging from DTI to warfarin).

  • Solution to dealing with unstable INRs in warfarin patients with lupus inhibitors
  • Eliminates the issues of varying sensitivities of different thromboplastins
  • Reliable, readily available, and easy to use assay
  • Applications for automated coagulation analyzers

Chromogenic Factor X assay test kit

  • Chromogenic Substrate Preparation 25 mg lyophilized FXa chromogenic substrate with mannitol added as a bulking agent. Reconstitute substrate with 20 ml sterile water. Storage & Stability The reconstituted substrate is stable for 6 months at 2 – 8°C.
  • Russell’s Viper Venom Preparation FX activating protein from Russell’s Viper Venom. Reconstitute the RVV with 15 ml sterile water. Storage & Stability The reconstituted activator is stable for 1 month at 2 – 8°C.
  • CaCl2 Preparation 20 ml of 0.1 mol/L calcium chloride solution. Before use, mix 1 volume of RVV with 1 volume of CaCl2. The mixture is stable for 48 hours at 2 – 8°C. Storage & Stability The solution is stable at 2 – 8°C until the expiry date printed on the label.
  • Buffer Preparation 100 ml buffer solution containing 0.05 mol/L Tris, pH 7.8 and 20 mg/L Polybrene® (hexadimethrine bromide). Ready for use. Storage & Stability The buffer is stable at 2 – 8°C until the expiry date printed on the label.

 

 

1

RVV
 FXFXa
Ca+2

2

Chromogenic SubstratePeptide + pNA (color)
FXa

The method is based on a two-stage principle. In stage one, Factor X is activated in the presence of calcium to Factor Xa (FXa) by the activator Russell’s Viper Venom (RVV). In stage two, the generated FXa hydrolyses the chromogenic substrate, thus liberating the chromophoric group, pNA. The color is then read with a spectrophotometer at 405 nm. The generated FXa and thus the intensity of color is proportional top the FX activity in the sample.

Coagulation Factor X (Stuart Prower Factor, FX) is a vitamin K dependent protein produced by the liver. It has a central position in the coagulation cascade. Factor X is activated both by the extrinsic and intrinsic systems before exerting its effect on the conversion of prothrombin to thrombin.

Patients who need anticoagulation therapy can be treated with warfarin, which is a vitamin K antagonist. This treatment leads to a decrease in all vitamin K dependent clotting factors and thus a prolonged clotting time of blood. The therapy requires careful monitoring since it is essential to find an optimal balance between risk of thrombosis and risk of bleeding for each patient. The DiaPharma Factor X kit is a useful tool in the management of patients with lupus inhibitors receiving warfarin therapy.

Factor X or anti-Xa Assay. Which Do I Use?
Factor X or anti-Xa Assay. Which Do I Use?

David L. McGlasson, MS, MLS(ASCP)cm, GA Fritsma, MS, MLS(ASCP)cm
59th Clinical Research Division
JBSA Lackland, TX

What is the therapeutic range for Factor X?
Each lab must determine its own reference range. Studies have shown that normal FX levels are about 70 – 130%, and therapeutic range is about 20 – 40%. A list of reference ranges found in the literature and at various reference laboratories can be obtained from DiaPharma.
What CPT code should I use for Factor X?
You can bill to CPT Code 85260
What can I use for calibrators & controls for Factor X?
Currently there are no calibrators or controls on the market that are assayed for chromogenic FX, just clotting FX. Most labs use normal plasma calibrators and controls. If you calibrate your assay using normal plasma, you can determine the % of normal FX in your patient sample. Calibration and control plasma is available from DiaPharma that are traceable to the International Standards supplied by NIBSC in accordance with WHO recommendations.
Do you have applications for the DiaPharma Factor X kit on automated coagulation analyzers?
Yes, we have applications for the ACL Advance, AMAX, BCS, STA, STA Compact, STA-R, and SysmexCA 1500, as well as for microplates. Our applications library is growing, so please check with DiaPharma for the latest updates.
Why can’t I just use a FX clotting assay?
Presence of a lupus inhibitor or thrombin inhibitor can interfere with the clotting assay. LA patients can produce antibodies that interfere with the phospholipid-dependent clotting reactions that are part of most PT assays. In contrast, the chromogenic factor X reaction does not require a phospholipid membrane surface, and the presence of an LA or DTI does not affect the chromogenic factor X assay.
What is the utility of the DiaPharma Factor X kit? Am I expected to use this on ALL my Coumadin patients?
No, only for those where the INR is unreliable and unstable. For example, it is useful in patients with lupus anticoagulant where the LA falsely prolongs the PT, therefore giving unreliable INRs. Also, Argatroban has been shown to prolong the PT, so patients being bridged from Argatroban to warfarin can be monitored using the DiaPharma Factor X kit.
What is the DiaPharma Factor X kit?
The DiaPharma Factor X Kit is an in vitro diagnostic test kit for the quantitative determination of Factor X activity in human citrated plasma. Factor X activity is useful for monitoring patients on oral anticoagulant therapy (warfarin) where baseline INR values are prolonged and INR results are not reliable, such as in OAC patients with lupus inhibitors. The DiaPharma Factor X Kit is also useful for screening for factor X deficiencies.
If I want to determine FX in plasma, but do not want to buy a kit, what other options are there?
S-2337™ was previously included in the now discontinued Chromogenix Coatest® FX kit, so another substrate must be employed. S-2765™, which is also a substrate for FXa, can therefore be used, and a method based on the activation of FX in the presence of calcium using Russell’s Viper Venom (RVV) as the activator is described in the Chromogenix catalog. DiaPharma has composed a new DiaPharma Factor X kit based on S-2765™.
Protein concentrations in plasma
ComponentMolecular
Weight kDa
Plasma
Concentration
mg/l
Plasma
Concentration
μmol/l
Fibrinogen33030009
Prothrombin721502
Factor V330200.05
Factor VII500.50.01
Factor VIII3300.10.0003
Factor IX5650.09
Factor X5980.13
Factor XI16050.03
Factor XII80300.4
Factor XIII320100.03
Protein C6240.06
Protein S7010 (free)0.14
Protein Z6220.03
Prekallikrein86500.6
HMW kininogen120700.6
Fibronectin4503000.7
Plasminogen922002
t-PA600.0050.0001
Urokinase530.0040.0001
Antithrombin581452.5
Heparin Cofactor II66801.2
Plasmin Inhibitor63601
Protein C Inhibitor5740.07
α2-Macroglobulin72520003