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Test ID 11INE Factor XI Inhibitor Evaluation, Plasma


Advisory Information


This test is for factor XI inhibitors only. If the presence or type of inhibitor is unknown, order APROL / Prolonged Clot Time Profile, Plasma first, except for when screening studies are needed for patients with known hemophilia A or B.



Shipping Instructions


Send all vials in the same shipping container.



Necessary Information


If priority specimen, mark request form, give reason, and request a call-back.

Specimen Required


Patient Preparation:

1. Patient should not be receiving Coumadin (warfarin), heparin, direct thrombin inhibitors (argatroban, dabigatran), or direct factor Xa inhibitors (apixaban, rivaroxaban, and edoxaban).

2. Fasting preferred.

Specimen Type: Platelet-poor plasma

Collection Container/Tube: Light-blue top (3.2% sodium citrate)

Submission Container/Tube: 3 Plastic vials

Specimen Volume: 3 mL in 3 plastic vials, each containing 1 mL

Collection Instructions:

1. Specimen must be collected prior to factor replacement therapy.

2. For complete instructions, see Coagulation Guidelines for Specimen Handling and Processing in Special Instructions.

3. Centrifuge, transfer all plasma into a plastic vial, and centrifuge plasma again.

4. Aliquot plasma (1-2 mL per aliquot) into 3 separate plastic vials, leaving 0.25 mL in the bottom of centrifuged vial.

5. Freeze plasma immediately (no longer than 4 hours after collection) at -20° C or, ideally, ≤-40° C.

Additional Information:

1. Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.

2. Each coagulation assay requested should have its own vial.


Useful For

Detection and quantitation of inhibitor to coagulation factor XI

 

This test is not useful for the detection of a lupus-like circulating anticoagulant inhibitor, a nonspecific circulating anticoagulant, or other inhibitors that are not specific for coagulation factors.

Profile Information

Test ID Reporting Name Available Separately Always Performed
11INT FXI Inhib Profile Tech Interp No Yes
F_11 Coag Factor XI Assay, P Yes Yes

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
11AIH FXI Inhib Profile Prof Interp No No
11_IS Factor XI Inhib Scrn No No
GBETH General Factor Bethesda Units, P No No

Testing Algorithm

Testing begins with coagulation factor XI activity assay with dilutions to evaluate assay inhibition; if the factor XI activity assay is normal or increased, then a technical interpretation will be provided.

 

If the factor XI activity assay is decreased, then an inhibitor screen will be performed at an additional charge to look for specific factor XI inhibition and a professional interpretation will be provided. If specific inhibition is apparent, the titer of the inhibitor will be determined.

Method Name

Optical Clot-Based

Reporting Name

Factor XI Inhib Profile, P

Specimen Type

Plasma Na Cit

Specimen Minimum Volume

2 mL plasma in 2 plastic vials, 1 mL each

Specimen Stability Information

Specimen Type Temperature Time Special Container
Plasma Na Cit Frozen 14 days

Clinical Information

Factor XI inhibitors typically arise in patients with congenital XI deficiency (hemophilia C) or after infusion of fresh frozen plasma or factor XI concentrates. Acquired factor XI inhibitors rarely occur spontaneously.

Reference Values

FACTOR XI ACTIVITY ASSAY

Adults: 55-150%

Normal, full-term newborn infants or healthy premature infants may have decreased levels (≥10%) which may not reach adult levels for ≥180 days postnatal.*

*See Pediatric Hemostasis References section in Coagulation Guidelines for Specimen Handling and Processing in Special Instructions.

Interpretation

Normally, there is no inhibitor, ie, negative.

 

If the screening assays indicate the presence of an inhibitor, it will be quantitated and reported in Bethesda (or equivalent) units.

Clinical Reference

1. Hematology: Basic Principles and Practice. Seventh edition. Edited by R Hoffman, EJ Benz Jr, LE Silberstein, et al. Elsevier, 2018

2. Kasper CK: Treatment of factor VIII inhibitors. Prog Hemost Thromb 1989;9:57-86

3. Laboratory Hematology Practice. Edited by K Kottke-Marchant. Wiley Blackwell Publishing, 2012

Day(s) and Time(s) Performed

Monday through Friday

Analytic Time

1 day

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

85390-Factor XI Tech Interp

85270-Factor XI Assay

85335-Factor inhibitor Scrn (if appropriate)

85335-Bethesda units (if appropriate)

85390-Factor XI Professional Interp (if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
11INE Factor XI Inhib Profile, P In Process

 

Result ID Test Result Name Result LOINC Value
F_11 Coag Factor XI Assay, P 3226-8
11INT FXI Inhib Profile Tech Interp 69049-5

Forms

If not ordering electronically, complete, print, and send a Coagulation Test Request (T753) with the specimen.