Test Details
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 dilutions 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
Result Turnaround Time
2 - 3 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Use
This test is used to valuate isolated aPTT prolongation and to document specific factor deficiency.6-8
Special Instructions
If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted. Refer to Coagulation Collection Procedures for directions.
Limitations
Direct Xa or thrombin inhibitor therapy may cause factitiously low results.
Custom Additional Information
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
Specimen Requirements
Specimen
Plasma, frozen
Volume
1 mL
Container
Blue-top (sodium citrate) tube
Collection Instructions
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.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
Stability Requirements
| Temperature | Period |
|---|---|
| Frozen | 28 days |
| Freeze/thaw cycles | Stable x3 |
Reference Range
| Age | Range |
| 1 d | 7–41% |
| 3 d | 24–79% |
| 1 to 11 m | 62–125% |
| 1 to 10 y | 65–162% |
| 11 to 16 y | 65–139% |
| >16 y | 60–150% |
Storage Instructions
Freeze.
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.
Causes for Rejection
Severe hemolysis; improper labeling; clotted specimen; specimen diluted with IV fluids; samples thawed in transit; improper sample type; sample out of stability
References
Footnotes
10. Castellone DD, Castillo R, Depasse F et al. Determination of Coagulation Factor Activities Using the One-Stage Clotting Assay. CLSI Guideline H48. 2nd ed. Wayne, PA: Clinical and Laboratory Standards Institute (CLSI); 2016.
11. Riley PW, Gallea B, Valcour A. Development and Implementation of a Coagulation Factor Testing Method Utilizing Autoverification in a High-volume Clinical Reference Laboratory Environment. J Pathol Inform. 2017 Jun 19;8:25. PubMed 28706751
12. Monagle P, Barnes C, Ignjatovic V, et al. Developmental haemostasis. Impact for clinical haemostasis laboratories. Thromb Haemost. 2006 Feb;95(2):362-372. PubMed 16493500
13. Summerhayes R, et al. J Thromb Haemost. 2007;5(Supp 2):P-S-397.
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 086314 | Factor XI Activity | 3226-8 | 086314 | Factor XI Activity | % | 3226-8 |
| Order Code | 086314 | |||||
| Order Code Name | Factor XI Activity | |||||
| Order Loinc | 3226-8 | |||||
| Result Code | 086314 | |||||
| Result Code Name | Factor XI Activity | |||||
| UofM | % | |||||
| Result LOINC | 3226-8 |