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Test Code LAB309 Factor XI Assay, Blood or Plasma

Important Note

Please see the Coagulation Limitations under resources for effect of Anticoagulant drugs in this test.

Additional Codes


Reporting Title

Factor XI (11) Assay


End point Clot Detection

Used to detect factor XI deficiency.

Performing Laboratory

OhioHealth Laboratory Services-RMH Core Coagulation

Specimen Requirements

Submit only 1 of the following specimens:


Riverside Inpatients and Riverside Campus draw sites:

Testing must be performed within 4 hours of draw if submitting unprocessed whole blood.

Draw a full, light blue-top (citrate) tube; and send citrated whole blood. Invert several times to mix blood. Forward unprocessed whole blood promptly at ambient temperature only. Do not refrigerate. 


1. This assay requires its own specimen.

2. Gross hemolysis, icterus, and lipemia may affect results.

3. Indicate whole blood on request form.

4. Label specimen appropriately (whole blood).


Outpatients/Outreach Clients


Draw a full, light blue-top (citrate) tube. Spin down, remove plasma, spin plasma again, and place 1 mL of citrated platelet-poor plasma in plastic vial. (Glass vial is not acceptable.) Pour-off vial should be no more than 2/3 full. Send specimen frozen.

Note: 1. This assay requires its own specimen.

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


3. Gross hemolysis, icterus, and lipemia may affect results.

4. Indicate plasma on request form.

5. Label specimen appropriately (plasma).

Specimen Transport Temperature

Ambient/Refrigerate NO/Frozen NO-Blood

Frozen/Refrigerate NO/Ambient NO-Plasma

Reference Values


Critical value: <5%

Alerting category: First instance within 1 hour (initial result only, routine on results thereafter)

Day(s) Test Set Up

Monday through Friday

Test Classification and CPT Coding