Factor XIII Clot solubility(6).
Factor XIII, Qualitative
Fibrin Stabilizing Factor
This is a screening assay and will detect homozygous deficiency of factor XIII.
Factor XIII is a large (320 kilodalton) tetrameric molecule that is composed of two A-chains and two B-chains, A2B2. Factor XIII is activated by thrombin in the presence of calcium. The primary function of activated factor XIII (XIIIa) is to catalyze the formation of covalent bonds between fibrin molecules stabilizing the fibrin clot. Factor XIII converts loosely hydrogen-bonded monomers into covalently bonded fibrin polymer. The resultant clot has increased tensile strength and is resistant to fibrinolysis. Factor XIII deficiency should be considered when a patient with excessive bleeding has both normal protime (PT) and activated partial thromboplastin time (aPTT).
Congenital factor XIII deficiency is rare (less than one case per million individuals) and is inherited as an autosomal recessive trait. Individuals who are heterozygous for the deficiency are generally asymptomatic, although some cases of bleeding in heterozygotes have been reported with provocation. Homozygotes have symptoms than can present as umbilical stump bleeding, bleeding after circumcision, and excessive bleeding during teething.6 Intracranial hemorrhage can occur spontaneously in up to 30% of cases. The homozygous condition is associated with spontaneous abortions in females and infertility in males. Excessive bleeding can be observed after trauma or surgical procedures and wound healing can be delayed. Acquired deficiency can occur due to autoantibody production to factor XIII. Autoantibody development can sometimes occur in association with certain drugs, including isoniazid, penicillin, and phenytoin. Factor XIII levels can also become decreased in individuals with disseminated intravascular coagulation, severe liver disease, acute leukemia, Henoch-Schönlein purpura, Crohn’s disease, or ulcerative colitis.
Blue-top (sodium citrate) tube
Avoid warfarin (Coumadin®) therapy for two weeks and heparin therapy for two days prior to the test. Do not draw from an arm with a heparin lock or heparinized catheter.
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio. 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. 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. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.
Gross hemolysis; clotted specimen; frozen specimen thawed in transit; improper labeling