Test Overview
Chromogenic Substrate Assay
Monitoring warfarin anticoagulant therapy in patients whose plasma contains lupus anticoagulants and in patients receiving direct thrombin inhibitors.
A chromogenic factor X activity of approximately 20-40% corresponds to a 2.0-3.0 INR warfarin therapeutic range.
* Reference ranges may change over time. Please refer to the original patient report when evaluating results.
Test Details
2 hours
- Factor 10 Chromogenic
- Chromogenic Factor X Activity
- CFX
- Factor 10 Activity, Chromogenic
- Factor 10 Chromogenic
- INR Alternative
- Factor 10 Chromogenic Activity
Specimen Requirements
Collect specimen in a blue top (citrate 3.2%) tube. Mix by inversion. Specimen should arrive at lab within 3 hours of collection; transport at room temperature. Alternatively, centrifuge, aliquot plasma into a polypropylene plastic vial, and freeze the specimen within 4 hours of collection. Transport frozen specimen on dry ice. Collection of the blood through lines that have been previously flushed with heparin should be avoided. If the blood must be drawn through a VAD (vascular access device), the line should be flushed with 5 mL of saline and the first 5 mL of blood or six dead space volumes of the VAD discarded.
Additional Information
In most patients, the INR is used to monitor coumadin (warfarin) therapy. Lupus anticoagulants and direct thrombin inhibitors (e.g., argatroban, hirudin, dabigatran, bivalirudin) may produce prolonged prothrombin times which result in an INR that does not accurately reflect the level of anticoagulation. The chromogenic Factor X assay may be used to more accurately monitor warfarin therapy in these patients.