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Factor XI Activity

Plasma Thromboplastin Antecedent, Factor 11 Assay, Factor XI Assay

Test Codes

Antrim #26155, EPIC: LAB5186, FXI

Department

Coagulation

Instructions

Specimens with hematocrit values greater than 55% must have anticoagulant adjusted. Specimens must be re-collected using a specified whole blood to sodium citrate ratio. Contact the performing Laboratory for specific instructions.

Specimen Collection Criteria

Collect: One Light Blue-top 3.2% Sodium Citrate tube.

TUBE MUST BE FULL.

Physician Office/Draw Specimen Preparation

For optimal results, maintain whole blood specimen at room temperature (20-26°C or 68-78.8°F) prior to transport. Transport whole blood to the Laboratory within 4 hours of collection. If transport within 4 hours is not possible, the following procedure must be followed for accurate results:

1. Centrifuge the capped tube at 1500 x g for 15 minutes.
2. Transfer plasma with a plastic pipette into a plastic polypropylene centrifuge tube, cap and centrifuge an additional 15 minutes at 1500 x g to obtain platelet poor plasma (PPP) which has a platelet count less than 10 bil/L. Plasma with a platelet count of less than 10 bil/L is critical for accurate results.
3. Immediately remove only the top two-thirds of the PPP and transfer it into a screw cap, 5 ml, 75 x 13 mm, round base, polypropylene tube.
4. Freeze (-20°C/-4°F or below) the PPP immediately.
5. Transport frozen on DRY ICE. Specimen must remain frozen during transport.   

Preparation for Courier Transport

Transport: Whole blood at room temperature (20-25°C or 68-77°F), or plasma obtained through the process listed above, frozen (-20°C/-4°F or below).

Rejection Criteria

• Glass tubes and 3.8% Sodium Citrate tubes.
• Specimens that are clotted or grossly hemolyzed.
• Inappropriate specimen volume.
• Thawed or partially thawed specimens.

In-Lab Processing

Whole blood specimens must be processed as follows upon receipt in the Laboratory:

1. Centrifuge the capped tube at 1500 x g for 15 minutes.
2. Transfer plasma with a plastic pipette into a plastic polypropylene centrifuge tube, cap and centrifuge an additional 15 minutes at 1500 x g to obtain platelet poor plasma (PPP) which has a platelet count less than 10 bil/L. Plasma with a platelet count of less than 10 bil/L is critical for accurate results.
3. Immediately remove only the top two-thirds of the PPP and transfer it into a plastic tube.

4. Test or freeze specimen according to lab protocol.

Storage

Specimen Stability for Testing:

Whole Blood
Room Temperature (20-26°C or 68-78.8°F): 4 hours
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): Unacceptable

Plasma Aliquot
Room Temperature (20-26°C or 68-78.8°F): Unacceptable
Refrigerated (2-8°C or 36-46°F): Unacceptable
Frozen (-20°C/-4°F or below): 30 days

Specimen Storage in Department Prior to Disposal:

Frozen (-20°C/-4°F or below): 30 days

Laboratory

Royal Oak Coagulation Laboratory

Performed

Monday – Friday, 7:00 am – 3:30 pm.
Results available the next business day.

Reference Range

65-150%.

Test Methodology

Change in Optical Absorbance (IL ACL TOP Series).

Interpretation

Low levels may indicate Factor XI deficiency.

Clinical Utility

This assay aids in the diagnosis of Factor XI deficiency, and in the investigation of prolonged aPTT. There is a relatively high incidence of congenital deficiency among people of Ashkenazi Jewish descent (hemophilia C).

CPT Codes

85270

Contacts

Last Updated

4/10/2023