Home
HelpOrder Code 11INE Factor XI Inhibitor Evaluation, Plasma
Ordering Guidance
This test is for factor XI inhibitors only. If the presence or type of inhibitor is unknown, first order APROL / Prolonged Clot Time Profile, Plasma, except for patients with known hemophilia A or B. When screening studies are needed for patients with known hemophilia A or B, order 8INHE / Factor VIII Inhibitor Evaluation, Plasma; or 9 INHE / Factor IX Inhibitor Evaluation, Plasma; respectively.
Shipping Instructions
Send all vials in the same shipping container.
Necessary Information
Specimen Required
Specimen Type: Platelet-poor plasma
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.
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.
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 at -20° C or, ideally, at -40° C or below.
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.
Special Instructions
Method Name
F_11, 11_IS, GBETH: Optical Clot-Based
11INT: Technical Interpretation
11AIH: Medical Interpretation
Reporting Name
Factor XI Inhib Profile, PSpecimen Type
Plasma Na CitSpecimen Minimum Volume
2 Plastic vials, each containing 1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Plasma Na Cit | Frozen | 14 days |
Reject Due To
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | Reject |
Reference Values
FACTOR XI ACTIVITY ASSAY
Adults: 55-150%
Normal, full-term newborn infants or healthy premature infants may have decreased levels (≥10%) that may not reach adult levels for 180 days or more postnatal.*
*See Pediatric Hemostasis References section in Coagulation Guidelines for Specimen Handling and Processing.
FACTOR XI INHIBITOR SCREEN:
Negative
GENERAL FACTOR BETHESDA UNITS:
≤0.5 Bethesda Units
Method Description
This assay consists of measuring the difference in factor XI activity (activated partial thromboplastin time-based assay) before and after incubation of a mixture of normal plasma and patient's plasma for 1 hour at 37° C. For optimal sensitivity, the factor XI value of the normal plasma is adjusted to approximately 20%, because the factor XI assay is more sensitive in this area of the curve. In addition, an excess of patient's plasma will make the test more sensitive to small amounts of inhibitors.(Owen CA Jr, Bowie EJW, Thompson JH Jr. The Diagnosis of Bleeding Disorders. 2nd ed. Little, Brown, and Company, 1975, pp 143-145; Cielsa B. Defects of plasma clotting factors. In: Hematology in Practice. 3rd ed. FA Davis; 2019:chap 17)
If the inhibitor screen is positive for an inhibitor of factor XI, the inhibitor will be quantitated by the Bethesda assay. In the Bethesda procedure, inhibitors are quantified by mixing equal volumes of serially diluted plasma with normal plasma. This mixture is incubated 2 hours at 37° C, and the factor XI activity is measured and compared to a control run at the same time. The difference between the factor XI activity of the patient's incubation mixture and that of the control is used to calculate titer. The residual factor XI activity is converted to Bethesda units: 50% residual factor XI is equal to 1 Bethesda unit.(Kasper CK, Aldedort LM, Counts RB, et al. A more uniform measurement of factor VIII inhibitors. Thromb Diath Haemorrh 1975;34:869-872; Cielsa B. Defects of plasma clotting factors. In: Hematology in Practice. 3rd ed. FA Davis; 2019:chap 17)
Day(s) Performed
Monday through Friday
Performing Laboratory
Mayo Clinic Laboratories in Rochester
CPT Code Information
85390
85270
85335 (if appropriate)
85335 (if appropriate)
85390 (if appropriate)
Forms
If not ordering electronically, complete, print, and send a Coagulation Test Request (T753) with the specimen.