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HelpTest Code FXCH Coagulation Factor X Chromogenic Activity Assay, Plasma
Reporting Name
Factor X Chromogenic Activity AssayUseful For
Monitoring warfarin anticoagulant therapy, especially in patients whose plasma contains lupus anticoagulants that interfere with baseline prothrombin time/international normalized ratio and in patients receiving the drug Argatroban who are being transitioned to warfarin
This assay should not be used for monitoring heparin, or oral direct factor Xa inhibitors such as rivaroxaban (Xarelto), apixaban (Eliquis), or edoxaban (Savaysa).
Method Name
Chromogenic
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Plasma Na CitSpecimen Required
Patient Preparation: Fasting preferred
Collection Container/Tube: Light-blue top (citrate)
Submission Container/Tube: Polypropylene vial
Specimen Volume: 1 mL
Collection Instructions:
1. For complete instructions see Coagulation Guidelines for Specimen Handling and Processing
2. Spin down, remove plasma, and spin plasma again.
3. Freeze plasma immediately (no longer than 4 hours after collection) at -20° C or, ideally, at or below -40° C.
Additional Information:
1. Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.
2. Each coagulation assay requested should have its own vial.
3. If priority specimen, mark request form, give reason, and request a call-back.
Specimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Plasma Na Cit | Frozen | 14 days |
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | Reject |
Special Instructions
Reference Values
≥18 years of age: 60%-140%
Chromogenic Factor X activity generally correlates with the one-stage factor X activity. In full term or premature neonates, infants, and children, the one-stage factor X activity* is lower than adult reference range and progressively rises to the adult reference range by adolescence. However, no similar data for the chromogenic factor X activity have been published.
*See Pediatric Hemostasis References section in Coagulation Guidelines for Specimen Handling and Processing.
Day(s) Performed
Monday through Friday
CPT Code Information
85260
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| FXCH | Factor X Chromogenic Activity Assay | 33984-6 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| FXCH | Factor X Chromogenic Activity Assay | 33984-6 |
Clinical Information
The antithrombotic effect of oral vitamin K antagonists (eg, warfarin) is mediated by reduction in the plasma activity of vitamin K-dependent procoagulant factors II (prothrombin) and X. The intensity of oral anticoagulation therapy with vitamin K antagonists must be monitored and adjusted to a narrow therapeutic range; under medicating increases the risk of thrombosis, while overmedicating increases the risk of bleeding. Such therapy typically is monitored with the prothrombin time/international normalized ratio (INR) system.
Lupus anticoagulants (LAC) are autoantibodies that interfere with phospholipid-dependent clotting tests and most commonly cause prolongation of the activated partial thromboplastin time (APTT). LAC can be associated with a prothrombotic disorder termed the antiphospholipid syndrome. LAC occasionally may cause prolongation of the baseline prothrombin time, rendering the INR system inaccurate for monitoring the intensity of oral anticoagulant therapy. LAC-induced prolongation of the prothrombin time is most commonly seen with recombinant human tissue factor thromboplastins (ie, prothrombin time reagents) with a low international sensitivity index (ISI) such as Innovin or RecombiPlasTin 2G (ISI = 1.0). The chromogenic factor X activity is an alternative assay for monitoring oral anticoagulant therapy. This assay is unaffected by LAC because the assay end point is not a phospholipid-dependent clotting time.
Argatroban is a parenteral direct thrombin inhibitor that is approved for treatment of heparin-induced thrombocytopenia (HIT), an antibody-mediated prothrombotic disorder. Argatroban therapy prolongs the prothrombin time, which also renders the INR inaccurate for monitoring the warfarin effect while transitioning from Argatroban to oral anticoagulant therapy. The chromogenic coagulation factor X activity assay may be used as an alternative to the INR for monitoring and adjusting the warfarin dose during this transition.
Interpretation
A chromogenic factor X activity of approximately 20% to 40% corresponds to the usual warfarin international normalized ratio range (ie, 2.0-3.0).
Cautions
Liver disease and vitamin K deficiency may lower factor X levels. If factor X deficiency is suspected, order F_10 / Coagulation Factor X Activity Assay, Plasma.
Method Description
The chromogenic factor X assay is performed on the Instrumentation Laboratory ACL TOP. In this 2-stage assay, an incubated dilution of the patient's plasma is combined in equal volumes with a chromogenic substrate and a Russell's viper venom/calcium chloride reagent. The patient's plasma factor X is activated in the presence of calcium by the activator Russell's viper venom, which then hydrolyzes the chromogenic substrate creating 2 products, peptide and pNA (paranitroaniline). The pNA is then measured at 405 nm and is proportional to the amount of factor X in the patient's plasma.(Package insert: Diapharma Factor X Kit. DiaPharma Group, Inc., Rev 06/2006)