Test Catalog

Test ID: CH9    
Chromogenic Factor IX Activity Assay, Plasma

Useful For Suggests clinical disorders or settings where the test may be helpful

Monitoring coagulation factor replacement therapy of selected extended half-life coagulation factor replacements


Aiding in the diagnosis of hemophilia B using a 2-stage assay, especially when a 1-stage assay was normal

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

This assay is indicated in situations where there is a clinical suspicion of hemophilia B diagnosis, when the 1-stage assay is normal. However, this assay is also recommended for accurate classification of hemophilia B.


See Hemophilia Testing Algorithm in Special Instructions

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Factor IX (FIX) is a vitamin K-dependent serine protease synthesized in the liver and participates in the intrinsic coagulation pathway. Its biological half-life is 18 to 24 hours.


Congenital FIX deficiency is inherited as an X-linked recessive bleeding disorder (hemophilia B). Severe deficiency (<1%) characterized by hemarthroses, deep tissue bleeding, excessive bleeding with trauma, and ecchymoses.


Typically, these patients are tested using a 1-stage clotting assay. However, new treatment options using long-acting glycoPEGylated replacement products are being approved for clinical use. Pharmacokinetic studies for these products indicate ideal monitoring of patients should be performed by the 2-stage chromogenic assay.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.



Chromogenic Factor IX activity generally correlates with the one-stage FIX activity. In full term/premature neonates, infants, children, and adolescents the one-stage FIX activity* is similar to adults. However, no similar data for chromogenic FIX activity are available. (Appel JTH 2012; 10:2254)


*See Pediatric Hemostasis References section in Coagulation Guidelines for Specimen Handling and Processing in Special Instructions.

Interpretation Provides information to assist in interpretation of the test results

Factor IX deficiency may be acquired (eg, vitamin K deficiency, warfarin anticoagulation effect, liver disease, or a consumptive coagulopathy) or congenital (hemophilia B).


Optimal laboratory monitoring of selected extended half-life factor IX replacement therapy (eg, glycoPEGylated factor FIX) may be achieved with the chromogenic factor IX assay. Elevated factor IX levels may be associated with acute or chronic inflammation, excess factor IX replacement therapy, or as a result of a rare genetic variant, factor IX Padua.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Excess heparin and dilution contamination due to improper specimen collection through an intravenous access device may result in artifactually decreased results.


The 1-stage and chromogenic factor IX (FIX) assay results should correlate in the normal population, but may be discordant in the hemophilia population and when measuring factor replacement, especially with PEGylated recombinant FIX products.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Bowyer AE, Hillarp A, Ezban M, et al: Measuring factor IX activity of noacog beta pegol with commercially available one-stage clotting and chromogenic assay kits: a two-center study. J Thromb Haemost 2016 Jul;14(7 1428-1435 doi: 10.1111/jth.13348

2. Kitchen S, Signer-Romero K, Key NS: Current laboratory practices in the diagnosis and management of haemophilia: a global assessment. Haemophilia 2015 Jul;21(4)550-557

3. Sorensen MH, Anderson S, Ezban M: Factor IX-deficient plasma spiked with N9-GP behaves similarly to N9-GP post-administration clinical samples in N9-GP ELISA and FIX activity assays. Haemophilia 2015 Nov;21(6):832-836

4. Dodt J, Hubbard AR, Wicks SJ, et al: Potency determination of factor VIII and factor IX for new product labelling and postinfusion testing: challenges for caregivers and regulators. Haemophilia 2015 Jul;21(4):543-549

5. Wilmot HV, Hogwood J, Gray E: Recombinant factor IX: discrepancies between one-stage clotting and chromogenic assays. Haemophilia 2014 Nov;20(6):891-897

Special Instructions Library of PDFs including pertinent information and forms related to the test