Test Details
Methodology
Factor X is activated by Russell viper venom which, in turn, hydrolyzes a chromogenic substrate to produce color.
Result Turnaround Time
2 - 3 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Use
The chromogenic factor X activity test can be useful in monitoring patients on vitamin K antagonist therapy where baseline PT is prolonged.
Special Instructions
If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted. Refer to Coagulation Collection Procedures for directions.
Limitations
This assay should not be used for monitoring heparin or oral direct factor Xa inhibitors such as rivaroxaban (Xarelto), apixaban (Eliquis) or edoxaban (Savaysa).
Custom Additional Information
Lupus anticoagulants (LAC) can be associated with a prothrombotic disorder termed the antiphospholipid syndrome. LAC are autoantibodies that interfere with phospholipid-dependent clotting tests and most commonly cause prolongation of the activated partial thromboplastin time (APTT). LAC occasionally may cause prolongation of the baseline prothrombin time, rendering the INR system inaccurate for monitoring the intensity of oral anticoagulant therapy.1 Warfarin inhibits hepatic synthesis of factor X and the measurement of this factor by a chromogenic assay (CFX) is insensitive to LAC because the assay is not dependent on thromboplastin or fibrinogen. The CFX assay can be used to indirectly measure warfarin-associated anticoagulation in circumstances in which the interaction with thromboplastin or fibrinogen would render INR results unreliable.2-11 This assay is unaffected by LAC because the assay end point is not a phospholipid-dependent clotting time. There is an inverse linear relationship between CFX and INR.12,13 Recent publications have suggested that a CFX range of 20% to 40% corresponds to an INR range of 2.0 to 3.0.8-11
Specimen Requirements
Specimen
Plasma, frozen
Volume
1 mL
Container
Blue-top (sodium citrate) tube
Collection Instructions
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.14 Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio.15,16 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. With a winged blood collection set a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacuated tube.17,18 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternative anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentifuge for 10 minutes. Use a second plastic pipette to remove plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a Labcorp PP transpak frozen purple tube with screw cap (Labcorp No. 49482). Freeze immediately and maintain frozen until tested. To avoid delays in turnaround time when, please submit separate frozen specimens for each test requested.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
Stability Requirements
| Temperature | Period |
|---|---|
| Frozen | 28 days |
| Freeze/thaw cycles | Stable x3 |
Reference Range
• Nonanticoagulated subjects: 82% to 151%
• Anticoagulant therapeutic range: 20% to 40% corresponds to an INR range of 2.0−3.0
Storage Instructions
Freeze.
Causes for Rejection
Gross hemolysis; clotted specimen; frozen specimen thawed in transit; improper labeling
Footnotes
1. Robert A, Le Querrec A, Delahousse B, et al. Control of oral anticoagulation in patients with the antiphospholipid syndrome−influence of the lupus anticoagulant on International Normalized Ratio. Groupe Méthodologie en Hémostase du Groupe d'Études sur l'Hémostases et la Thrombose. Thromb Haemost. 1998 Jul;80(1):99-103. PubMed 9684793
2. Sanfelippo MJ, Zinsmaster W, Scherr DL, Shaw GR. Use of chromogenic assay of factor X to accept or reject INR results in warfarin treated patients. Clin Med Res. 2009 Sep;7(3):103-105. PubMed 19625497
3. Thom J, Ivey L, Gilmore G, Eikelboom JW. Evaluation of the phospholipid-rich dilute Russell’s viper venom assay to monitor oral anticoagulation in patients with lupus anticoagulant. Blood Coagul Fibrinolysis. 2004 Jun;15(4):353-357. PubMed 15166923
4. Arpino PA, Demirjian Z, Van Cott EM. Use of the chromogenic factor X assay to predict the international normalized ratio in patients transitioning from argatroban to warfarin. Pharmacotherapy. 2005 Feb;25(2):157-164. PubMed 15767231
5. Trask AS, Gosselin RC, Diaz JA, Dager WE. Warfarin initiation and monitoring with clotting factors II, VII, and X. Ann Pharmacother. 2004 Feb;38(2):251-256. PubMed 14742761
6. McGlasson DL, Romick BG, Rubal BJ. Comparison of a chromogenic factor X assay with international normalized ratio for monitoring oral anticoagulation therapy. Blood Coagul Fibrinolysis. 2008 Sep;19(6):513-517. PubMed 18685434
7. Moll S, Ortel TL. Monitoring warfarin therapy in patients with lupus anticoagulants. Ann Intern Med. 1997 Aug 1;127(3):177-185. PubMed 9245222
8. Mittal P, Sayar Z, Cohen H. Warfarin and heparin monitoring in antiphospholipid syndrome. Hematology Am Soc Hematol Educ Program. 2024 Dec 6;2024(1):192-199. PubMed 39644000
9. Cohen H, Efthymiou M, Devreese KMJ. Monitoring of anticoagulation in thrombotic antiphospholipid syndrome. J Thromb Haemost. 2021 Apr;19(4):892-908. PubMed 33325604
10. Greenmyer JR, Niaz T, Kohorst MA, Stephens EH, Anderson JH. Chromogenic Factor X Assay for Monitoring Warfarin Anticoagulation in a Child With a Prosthetic Mitral Valve. Mayo Clin Proc Innov Qual Outcomes. 2021 Aug 10;5(5):811-816. PubMed 34430797
11. Baumann Kreuziger LM, Datta YH, Johnson AD, Zantek ND, Shanley R, Reding MT. Monitoring anticoagulation in patients with an unreliable prothrombin time/international normalized ratio: factor II versus chromogenic factor X testing. Blood Coagul Fibrinolysis. 2014 Apr;25(3):232-236. PubMed 24681704
12. Efthymiou M, Lawrie AS, Mackie I, et al. Thrombin generation and factor X assays for the assessment of warfarin anticoagulation in thrombotic antiphospholipid syndrome. Thromb Res. 2015 Jun;135(6):1191-1197. PubMed 25895847
13. Tripodi A, Chantarangkul V, Clerici M, Negri B, Galli M, Mannucci PM. Laboratory control of oral anticoagulant treatment by the INR system in patients with the antiphospholipid syndrome and lupus anticoagulant. Results of a collaborative study involving nine commercial thromboplastins. Br J Haematol. 2001 Dec;115(3):672-678. PubMed 11736953
14. Adcock DM, Kressin DC, Marlar RA. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol. 1997 Jan;107(1):105-110. PubMed 8980376
15. Reneke J, Etzell J, Leslie S, Ng VL, Gottfried EL. Prolonged prothrombin time and activated partial thromboplastin time due to underfilled specimen tubes with 109 mmol/L (3.2%) citrate anticoagulant. Am J Clin Pathol. 1998 Jun;109(6):754-757. PubMed 9620035
16. Clinical and Laboratory Standards Institute (CLSI). Collection, Transport and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays. 6th ed. CLSI guideline H21. Clinical and Laboratory Standards Institute; 2024.
17. Gottfried EL, Adachi MM. Prothrombin time and activated partial thromboplastin time can be performed on the first tube. Am J Clin Pathol. 1997 Jun;107(6):681-683. PubMed 9169665
18. McGlasson DL, More L, Best HA, Norris WL, Doe RH, Ray H. Drawing specimens for coagulation testing: Is a second tube necessary? Clin Lab Sci. 1999 May-Jun;12(3):137-139. PubMed 10539100
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 117904 | Factor X, Chromogenic | 28657-5 | 117908 | Factor X, Chromogenic | % | 28657-5 |
| Order Code | 117904 | |||||
| Order Code Name | Factor X, Chromogenic | |||||
| Order Loinc | 28657-5 | |||||
| Result Code | 117908 | |||||
| Result Code Name | Factor X, Chromogenic | |||||
| UofM | % | |||||
| Result LOINC | 28657-5 |