Test Overview
Test Methodology

Chromogenic Substrate Assay

Test Usage

Monitoring warfarin anticoagulant therapy in patients whose plasma contains lupus anticoagulants and in patients receiving direct thrombin inhibitors.

Reference Range *

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
Days Set Up
Daily, 24 hours.
Analytic Time

2 hours

Soft Order Code
MiChart Code
Factor X Chromogenic Activity
  • Factor 10 Chromogenic
  • Chromogenic Factor X Activity
  • CFX
  • Factor 10 Activity, Chromogenic
  • Factor 10 Chromogenic
  • INR Alternative
  • Factor 10 Chromogenic Activity
Specimen Requirements
Collection Instructions

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.

Normal Volume
Full 2.7 mL tube or 1 mL plasma aliquot
Minimum Volume
Full 1.8 mL tube or 1 mL plasma aliquot
Storage Temperature
Room temperature for whole blood or frozen aliquot of citrated plasma.
Rejection Criteria
Specimens will be rejected if not properly filled, clotted, grossly hemolyzed, or contaminated with heparin.
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.

CPT Code
Fee Code