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- Fitzgerald Factor
Useful in the evaluation of an elevated aPTT. Measurement of high molecular weight kininogen concentration
High molecular weight kininogen (HMWK) is a 110 kilodalton single-chain nonenzymatic cofactor synthesized in the liver which is central to contact activation reactions.6 It forms a complex with prekallikrein and factor XI. HMWK's plasma concentration is 70 mg/mL and its plasma half-life is approximately 144 hours. Factors VIII, IX, XI, XII, prekallikrein, and HMWK are the coagulation factors of the intrinsic coagulation pathway. Factor XII, high molecular weight kininogen, and prekallikrein are also called the “contact” factors. Factor XI is sometimes included in this designate of “contact” factors because of its interaction with others listed. Factor XI is activated by factor XIIa formed through activation of XII by HMWK-prekallikrein complex on endothelial cells. HMWK proteolysis leads to the production of bradykinin, a mediator of vasodilation, smooth muscle contractions, and increased vascular permeability. Other functions of HMWK include inhibition of thrombin-induced platelet aggregation, participant in fibrinolysis, as well as having surface-binding antiadhesive properties. Contact factor deficiencies have no hemorrhagic consequence; however, the contact factors are necessary for normal aPTT clot formation in the laboratory. Deficiency of HMWK produces markedly prolongs aPTT results. Hereditary HMWK deficiency conditions are inherited through an autosomal recessive pattern. Although the aPTT is prolonged in deficiencies of factor XII, prekallikrein, and high molecular weight kininogen, there is generally no clinical evidence of bleeding unless other contributing factors are present. These deficiencies are generally diagnosed when evaluating a prolonged aPTT with no other explanation (ie, other screening tests) and clinical history is negative for a bleeding disorder.
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, except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used.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 alternate 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 and carefully remove the plasma using a plastic transfer pipette, being careful not to disturb the cells. Transfer the plasma into a LabCorp PP transpak frozen purple tube with screw cap (LabCorp N° 49482). Freeze immediately and maintain frozen until tested. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
|Order Code||Order Code Name||Order Loinc||Result Code||Result Code Name||UofM||Result LOINC|
|500460||High Molecular Weight||500461||Kininogen Activity||%||52754-9|
|500460||High Molecular Weight||500998||HMWK||N/A|