CDOS

Factor XI Activity

Test Code: 086314

Performing Lab: LabCorp

CPT Code: 85270 001

Test Link (Copy)

Synonym

Antihemophilic Factor C; Plasma Thromboplastin Antecedent (PTA)

Specimen Type

Plasma, FROZEN

Specimen Container

Blue-top (sodium citrate) tube

Volume

1 mL

Specimen Handling

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 evacutated 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. Print and use the Specimen Collection Bulletin as a tube-filling guide. specimens for each test requested. Print and use the Specimen Collection Bulletin as a tube-filling guide.

Patient Prep

Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadinr) 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.

Unacceptable Conditions

Severe hemolysis; improper labeling; clotted specimen; specimen diluted with I.V. fluids; samples thawed in transit; improper sample type; sample out of stability

Temperature

FREEZE

Methodology

The assay consists of the measurement of the clotting time, in the presence of cephalin and activator in a system in which all the factors are present and in excess except factor XI which is derived from the sample being tested. Testing coagulation factor activities requires that three diutions be assayed and analyzed to produce a single result. [10,11] The slope of the line created by plotting measured factor concentration against sample dilution is evaluated to discern the presence of inhibitors giving rise to nonparallelism.[11] Moreover, samples producing results on initial dilution falling outside the analytic measurement range of the assay are tested at additional dilutions to produce reportable results.[11]

Stability

Frozen: 28 days

Result Code	Result Name	LOINC
086314	Factor XI Activity	3226-8

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