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Evaluate isolated aPTT prolongation and to document specific factor deficiency.6-8
Factor XI activity is determined utilizing an aPTT-based one-stage clotting time assay. Factor XI-depleted plasma is used as the substrate, and the clotting time with the patient plasma is compared to the clotting time of normal pooled plasma.
Factor XI is a 160 kilodalton glycoprotein proenzyme that is produced by the liver and megakaryocytes.6-8 Factor XI's plasma concentration is 4-6 mg/mL and half-life is about 60 hours.6 Hereditary factor XI deficiency, referred to as hemophilia C, is transmitted as an autosomal recessive mutation.6-8 This condition affects both males and females and the majority of reported cases have been diagnosed in Ashkenazi Jews.6,7 As many as 11% of Ashkenazi Jews will be heterozygous for factor XI deficiency and up to 0.3% will be homozygous.8 Individuals who are heterozygous for factor XI deficiency mutation typically have levels between 30% to 60% and homozygotes have levels <20%.8 The bleeding associated with factor XI deficiency is generally not as severe as that found with hemophilia A or B.7 Severity of bleeding does not always correlate with the plasma level of factor XI.6,7 Individuals with factor XI deficiency can suffer from easy bruising, epistaxis, hematuria, and menorrhagia.6,7 Excessive bleeding postpartum and after oral cavity surgery can occur.7
Acquired inhibitors of factor XI are very rare.6 Spontaneous autoantibodies are more common and generally occur in patients with underlying autoimmune disorders or in patients treated with chlorpromazine.6
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, 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
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. Roberts HR, Escobar MA. Less common congenital disorders of hemostasis. In: Kitchens CS, Alving BM, Kessler CM, eds. Consultative Hemostasis and Thrombosis. Philadelphia, Pa: WB Saunders Co; 2002: 57-71.
8. Triplett DA. Coagulation abnormalities. In: McClatchey KD, ed. Clinical Laboratory Medicine. 2nd ed. Philadelphia, Pa: Lippincott Williams and Wilkins; 2002:1033-1049.
