Factor IX Assay
- Author: Bishnu Prasad Devkota, MD, MHI, FRCS(Edin), FRCS(Glasg), FACP; Chief Editor: Eric B Staros, MD more...
Factor IX (plasma thromboplastin component [PTC]) is produced in the liver. It is a single-chain zymogen with a molecular weight of 57 kd and a plasma half-life of 18-24 hours. It binds effectively to collagen not only in vitro but also, apparently, in vivo, and this may account for the finding that when factor IX is infused into hemophilia B patients, recovery is only 50% of what was expected.
The reference range for factor IX is between 70% and 120% of normal values.
Elevated factor IX concentrations are linked with an increased risk of thromboembolism. The following are associated with increases in factor IX:
Use of oral contraceptives
The following are associated with decreases in factor IX :
Use of vitamin K antagonists (eg, warfarin) or vitamin K deficiency
Alloantibodies in hemophilia B patients treated with factor IX infusions
Autoantibodies to factor IX in previously healthy individuals (extremely rare)
Collection and Panels
Collection approach and panels for factor IX are as follows:
Container: Blue-top vacuum tube
Collection method: Routine venipuncture
Packing: To comply with Occupational Safety and Health Administration (OSHA) safety standards, samples must be sent in a leakproof sealed container labeled with a biohazard sticker
Panels: Quantitative functional assays of coagulation factors
Factor IX is produced in the liver. It circulates as a single-chain zymogen with a molecular weight of 57 kd and a plasma half-life of 18-24 hours. It binds effectively to collagen not only in vitro but also, apparently, in vivo, and this may account for the finding that when factor IX is infused into hemophilia B patients, recovery is only 50% of what was expected. The physiologic relevance of this finding is not yet clear; there is some evidence that factor IX mutants lacking collagen-IV binding may exhibit greater recovery but may be associated with a mild bleeding tendency.[4, 5]
Either activated factor XI (XIa) or the activated factor VII (VIIa)–tissue factor complex may activate factor IX. Activated factor IX (IXa), complexed with activated factor VIII (VIIIa) on a phospholipid membrane surface, activates factor X, and activity normally expressed on the surface of activated platelets. Platelets express a receptor/binding protein for factor IXa that promotes assembly of the IXa/VIIIa complex.
Antithrombin (AT) is the primary inhibitor of factor IXa. Such inhibition, though notably slower than the inhibition of thrombin by AT, is enhanced in the presence of heparin.
The gene for factor IX is found on the X chromosome (on the tip of the long arm), indicating that factor IX deficiency is sex-linked. Christmas disease (hemophilia B) is caused by the deficiency of factor IX and is treated with factor IX replacement. Products available on the market include prothrombin complex concentrates (PCCs), which contain prothrombin, factors VII and X, and proteins C and S in addition to factor IX. PCCs may also contain small amounts of factors VIIa, IXa, and Xa. They may be less expensive than purified factor IX products.
Thromboembolism related to PCC use derives from contamination with activated components. In factor IX-deficient patients with liver dysfunction, inability of the diseased liver to clear the activated factors may lead to thrombosis. Large PCC doses have led to reports of deep vein thrombosis (DVT) and disseminated intravascular coagulation (DIC) in some cases. The preparations now available, however, are less likely to give rise to these complications. As a general rule, if PCCs are to be used for replacement therapy, factor IX levels should not exceed 50% of normal.
Some highly purified factor IX products are derived from human plasma. Although factor IX products synthesized via recombinant DNA technology prevent transmission of prion disease, they are generally associated with lower intravascular recovery of factor IX than purified factor IX products prepared from plasma are. Recombinant factor IX products appear not to give rise to thrombosis. With regard to transmission of hepatitis B and C viruses and HIV, currently available factor IX concentrates are safe, though transmission of these viruses may have occurred in patients treated before 1985.
Inhibitors may develop in factor IX –deficient patients exposed to factor concentrates early in life. In hemophilia B patients undergoing surgical procedures, tranexamic acid may help reduce the risk of perioperative bleeding.
Factor IX testing is indicated in the following situations:
Hemophilia B is suspected
The clinician needs to differentiate the effects of oral anticoagulants from those of liver disease
Of the more than 100 factor IX gene mutations that have been identified, many cause bleeding diatheses, though some do not give rise to significant symptoms; a few may result in thromboembolism.
Factor IX deficiency does not affect the prothrombin time (PT) appreciably; however, it does prolong the partial thromboplastin time (PTT) when the factor IX level falls to less than 40% of the normal value.
The following factors may decrease the accuracy of the PT :
Partial clotting of specimens, resulting from improper mixture of the anticoagulant (3:2 sodium citrate, as per the manufacturer’s blue-top tube)
Overfilling or underfilling of test tubes, either of which alters the blood-to-anticoagulant ratio (9:1)
Analytical errors (eg, lipemic, icteric, or hemolyzed plasma), which may interfere with photoelectric measuring instruments
Wolberg AS, Stafford DW, Erie DA. Human factor IX binds to specific sites on the collagenous domain of collagen IV. J Biol Chem. 1997 Jul 4. 272(27):16717-20. [Medline].
Williamson MA, Snyder LM, Wallach JB. Wallach's interpretation of diagnostic tests. 9th ed. Wolters Kluwer/Lippincott Williams & Wilkins Health: Philadelphia; 2011.
Cheung WF, van den Born J, Kuhn K, Kjellen L, Hudson BG, Stafford DW. Identification of the endothelial cell binding site for factor IX. Proc Natl Acad Sci U S A. 1996 Oct 1. 93(20):11068-73. [Medline].
Gui T, Lin HF, Jin DY, Hoffman M, Straight DL, Roberts HR. Circulating and binding characteristics of wild-type factor IX and certain Gla domain mutants in vivo. Blood. 2002 Jul 1. 100(1):153-8. [Medline].
Gui T, Reheman A, Ni H, Gross PL, Yin F, Monroe D. Abnormal hemostasis in a knock-in mouse carrying a variant of factor IX with impaired binding to collagen type IV. J Thromb Haemost. 2009 Nov. 7(11):1843-51. [Medline].
Monroe DM HM, Roberts HR. Molecular Biology and Biochemistry of the Coagulation Factors and Pathways of Hemostasis. Prchal JT KK, Lichtman MA, Kipps TJ, Seligsohn U, ed. Williams Hematology. 8th ed. McGraw-Hill: New York; 2010.
Camerino G, Grzeschik KH, Jaye M, De La Salle H, Tolstoshev P, Lecocq JP. Regional localization on the human X chromosome and polymorphism of the coagulation factor IX gene (hemophilia B locus). Proc Natl Acad Sci U S A. 1984 Jan. 81(2):498-502. [Medline].
Biggs R, Douglas AS, Macfarlane RG, Dacie JV, Pitney WR, Merskey. Christmas disease: a condition previously mistaken for haemophilia. Br Med J. 1952 Dec 27. 2(4799):1378-82. [Medline].
Roberts HR KN, Escobar MA. Hemophilia A and Hemophilia B. Prchal JT KK, Lichtman MA, Kipps TJ, Seligsohn U. Williams Hematology. McGraw-Hill: New York; 2010.
White GC 2nd, Beebe A, Nielsen B. Recombinant factor IX. Thromb Haemost. 1997 Jul. 78(1):261-5. [Medline].
Rossi M, Jayaram R, Sayeed R. Do patients with haemophilia undergoing cardiac surgery have good surgical outcomes?. Interact Cardiovasc Thorac Surg. 2011 Sep. 13(3):320-31. [Medline].
Simioni P, Tormene D, Tognin G, Gavasso S, Bulato C, Iacobelli NP. X-linked thrombophilia with a mutant factor IX (factor IX Padua). N Engl J Med. 2009 Oct 22. 361(17):1671-5. [Medline].