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HelpTest ID F_12 Coagulation Factor XII Activity Assay, Plasma
Reporting Name
Coag Factor XII Assay, PUseful For
Diagnosing deficiency of coagulation factor XII
Determining cause of prolonged activated partial thromboplastin time
Specimen Type
Plasma Na CitOrdering Guidance
Coagulation testing is highly complex, often requiring the performance of multiple assays and correlation with clinical information. For that reason, consider ordering a Coagulation Consultation.
Necessary Information
If priority specimen, mark request form, give reason, and request a call-back.
Specimen Required
Specimen Type: Platelet-poor plasma
Patient Preparation: Patient must not be receiving Coumadin (warfarin) or heparin therapy.
Collection Container/Tube: Light-blue top (3.2% sodium citrate)
Submission Container/Tube: Plastic vial
Specimen Volume: 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 into a plastic vial, 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, at or below -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.
Specimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Plasma Na Cit | Frozen | 14 days |
Reference Values
Adults: 55-180%
Normal, full-term newborn infants or healthy premature infants may have decreased levels (≥15% to 20%), which may not reach adult levels for 180 or more days postnatal.*
*See Pediatric Hemostasis References section in Coagulation Guidelines for Specimen Handling and Processing.
Day(s) Performed
Monday through Saturday
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 US Food and Drug Administration.CPT Code Information
85280
Clinical Information
Factor XII is synthesized in the liver. Its biological half-life is 40 to 50 hours. Factor XII is a component of the contact activation system and is involved in both intrinsic pathway and fibrinolytic system.
Factor XII deficiency is often discovered when activated partial thromboplastin time is found to be unexpectedly long. The deficiency does not cause a known bleeding disorder.
An association between severe factor XII deficiency and thrombosis risk has been proposed but not proven.
Interpretation
Acquired deficiency is associated with liver disease, nephritic syndrome, and chronic granulocytic leukemia.
Congenital homozygous deficiency: 20% activity
Congenital heterozygous deficiency: 20% to 50% activity
Cautions
Deficiencies of other contact activator proteins (prekallikrein, high molecular weight kininogen) can also cause prolonged activated partial thromboplastin time but do not cause clinical bleeding.
Clinical Reference
1. Renne T, Schmaier AH, Nickel KF, Blomback M, Maas C. In vivo roles of factor XII. Blood. 2012;120(22):4296-4303
2. Favaloro EJ, Lippi G, eds. Hemostasis and Thrombosis: Methods and Protocols. Humana Press; 2017
Method Description
The factor XII assay is performed on the Instrumentation Laboratory ACL TOP using the activated partial thromboplastin time (aPTT) method and a factor-deficient substrate. Patient plasma is combined and incubated with a factor XII-deficient substrate (normal plasma depleted of factor XII by immunoadsorption) and an aPTT reagent. After a specified incubation time, calcium is added to trigger the coagulation process in the mixture. Then the time to clot formation is measured optically at a wavelength of 671 nm.(Owen CA Jr, Bowie EJW, Thompson JH Jr. Diagnosis of Bleeding Disorders. 2nd ed. Little, Brown and Company; 1975; Cielsa B. Defects of plasma clotting factors. In: Hematology in Practice. 3rd ed. FA Davis; 2019:chap 17)
Report Available
1 to 3 daysReject Due To
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | Reject |
NY State Approved
YesMethod Name
Optical Clot-Based
Forms
If not ordering electronically, complete, print, and send a Coagulation Test Request (T753) with the specimen.