Factor IX Activity (Antihemophilic Factor B)

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Turnaround Time: 2 - 3 days
CPT Code:


Test Type: 1 mL Plasma, frozen


Evaluate an isolated, prolonged aPTT and to document specific factor IX deficiency6-9.

Direct Xa or thrombin inhibitor therapy may cause factitiously low results. Factor IX levels can be diminished in severe liver disease and in vitamin K-deficient patients. This can affect the accuracy of the test in diagnosing hemophilia. Factor IX levels should not be used to determine the carrier status of females. Genetic testing should be used for this purpose. Factor IX inhibitors (both alloantibodies that develop after replacement therapy and autoantibodies that develop spontaneously) can result in falsely low factor IX levels.10,11

Factor IX is a 72 kilodalton vitamin K-dependent glycoprotein proenzyme that is produced by the liver.6 Factor IX's plasma concentration is 3-5 mg/mL and half-life is about 24 hours.6 Factor IX deficiency should be suspected when a patient with excessive bleeding has a normal protime (PT) and an extended activated partial thromboplastin time (aPTT). Hemophilia B, or Christmas disease, occurs as the result of congenital deficiency of factor IX.6,7 Clinical features of hemophilia B are the same as for hemophilia A which is caused by factor VIIIdeficiency (see Factor VIII Activity [086264]).

Hemophilia B is less common than hemophilia A, occurring in approximately 1 of every 30,000 live male births.7 The prevalence is significantly higher in Amish and East Indian populations.8 This condition is transmitted as an X chromosome-linked hereditary disorder.7 The majority of cases occur in men whose mothers are carriers of the genetic defect. A subtype of hemophilia B, hemophilia B Leiden, is characterized by altered developmental expression of factor IX such that plasma factor IX levels may be <1% of normal during childhood, but after puberty may gradually rise to a maximum of 70% of normal.12 Hemophilia B can also occur as the result of spontaneous mutations of the factor IX gene locus.7 Female carriers of hemophilia B may rarely present with excessive bleeding.7 Hemophilia symptoms can also occur in female carriers that have a high degree of lyonization of the factor X alleles.7 Females with Turner syndrome, karyotype XO, can also be symptomatic.7

The severity of hemophilia B can be defined by the level of factor IX activity.7,8 Severe hemophilia is associated with a factor IX level of <1%. Moderate hemophilia B occurs with factor IX levels of 1% to 5% and mild hemophilia has factor IX levels >5%.

Patients with hemophilia B can present with any of a number of bleeding manifestations.6,7 Often, infants with severe hemophilia are first diagnosed during the neonatal period because of excessive bleeding after circumcision or due to cord necrosis.7 Hemophilic infants also frequently suffer from intracranial hemorrhage or scalp hematomas. Spontaneous hemarthroses, a common symptom of hemophilias, typically do not occur until the child starts walking.7,8 Hematomas can often be observed at the sites of intramuscular injections for vaccination or medication. The most common sites of spontaneous bleeding in patients with severe hemophilia are involve the joints and muscles. Recurrent bleeding leads to chronic muscle injury and degeneration of the joint tissue.6,7 Gastrointestinal bleeding can occur in approximately 10% of hemophiliacs.7 Males with mild to moderate hemophilia and female carriers may have an increased bleeding tendency, especially following surgery or trauma.8

Acquired factor IX deficiency can occur as the result of oral anticoagulant therapy or with vitamin K deficiency.6,8 Individuals with advance liver disease can have a generalized decrease in coagulation factors, including factor IX.

Elevation of factor IX, if persistent, has been associated with approximately a twofold increased risk for venous thrombosis.9 The basis for this increased risk is not well understood and the clinical cutoff for risk assessment has yet to be established.9

Hemophilia B patients receiving replacement products can develop inhibitors to factor IX in approximately 3% of cases, due to the production of alloantibodies.6,10 Acquired hemophilia caused by the development of autoantibodies to factor IX can also occur.11 This rare condition can occurs most often in individuals with autoimmune disorders. These patients have bleeding symptoms similar to those seen in congenital hemophilia B.

1. 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

2. Reneke J, Etzell J, Leslie S, et al. 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

3. National Committee for Clinical Laboratory Standardization. Collection, Transport, and Processing of Blood Specimens for Coagulation Testing and General Performance of Coagulation Assays; Approved Guideline. 5th ed. Villanova, Pa: NCCLS; 2008. Document H21-A5:28(5)

4. 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

5. 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

6. Adcock DM, Bethel MA, Macy PA. Coagulation Handbook. Aurora, Colo: Esoterix-Colorado Coagulation; 2006.

7. Cohen AJ, Kessler CM. Hemophilia A and B. In: Kitchens CS, Alving BM, Kessler CM, eds. Consultative Hemostasis and Thrombosis. Philadelphia, Pa: WB Saunders Co; 2002: 43-56.

8. Triplett DA. Coagulation abnormalities. In: McClatchey KD, ed. Clinical Laboratory Medicine. 2nd ed. Philadelphia, Pa: Lippincott Williams and Wilkins; 2002:1033-1049.

9. Chandler WL, Rogers GM, Sprouse JT, Thompson AR. Elevated hemostatic factor levels as potential risk factors for thrombosis. Arch Pathol Lab Med. 2002 Nov; 126(11):1405-1414. PubMed 12421150

10. Dimichele D. Inhibitors: Resolving diagnostic and therapeutic dilemmas. Haemophilia. 2002 May; 8(3):280-287. PubMed 12010424

11. Boggio LN, Green D. Acquired hemophilia. Rev Clin Exp Hematol. 2001 Dec; 5(4):389-404. PubMed 11844135

Adcock DM, Gosselin R. Direct oral anticoagulants (DOACs) in the laboratory: 2015 review. Thromb Res. 2015 Jul; 136(1):7-12. PubMed 25981138

Reijnen MJ, Sladek FM, Bertina RM, Reitsma PH. Disruption of a binding site for a hepatic nuclear factor 4 results in hemophilia B Leyden. Proc Natl Acad Sci USA. 1992 Jul 15; 89(14):6300-6303. PubMed 1631121

Collection Details:

Patient Preparation:

Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa, and thrombin inhibitor therapies for about three days prior to testing. Do not draw from an arm with a heparin lock or heparinized catheter.

Collection Instructions:

If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted.

Blue-top (sodium citrate) tube.

Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio.2,3 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.4,5 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.