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Test ID 9INHE Factor IX Inhibitor Evaluation, Plasma


Ordering Guidance


This test is for factor IX inhibitors only. If the patient is known to have hemophilia B, this is the correct test to order. If the presence or type of inhibitor is unknown, first order APROL / Prolonged Clot Time Profile, Plasma. When screening studies are needed for patients with known hemophilia A, order 8INHE / Factor VIII Inhibitor Evaluation, Plasma.



Shipping Instructions


Send all vials in the same shipping container.



Necessary Information


 



Specimen Required


Specimen Type: Platelet-poor plasma

Patient Preparation:

1. Patient must not be receiving Coumadin (warfarin) or heparin therapy

2. Fasting preferred

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

Submission Container/Tube: 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 (no longer than 4 hours after collection) 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 titering of coagulation inhibitor to the specific factor requested, primarily factor IX in patients with hemophilia B

 

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.

Disease States

  • Hemophilia B

Profile Information

Test ID Reporting Name Available Separately Always Performed
9INHT FIX Inhib Profile Tech Interp No Yes
F_9 Coag Factor IX Assay, P Yes Yes

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
9AINH FIX Inhib Profile Prof Interp No No
9BETH FIX Bethesda Units, P No No
F9_IS Factor IX Inhib Scrn No No

Testing Algorithm

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

 

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

Method Name

F_9, 9BETH, F9_IS: Optical Clot-Based

9INHT: Technical Interpretation

9AINH: Medical Interpretation

Reporting Name

Factor IX Inhib Profile, P

Specimen Type

Plasma Na Cit

Specimen 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

Clinical Information

Factor IX inhibitors arise in patients with severe hemophilia B after factor IX transfusion. Patients with factor IX inhibitors may also develop anaphylactic reactions in response to factor IX infusions. Acquired factor IX inhibitors, occurring in previously healthy people, are exceedingly rare.

Reference Values

FACTOR IX ACTIVITY ASSAY

Adults: 65-140%

Normal, full-term newborn infants or healthy premature infants may have decreased levels (≥20%) 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 IX INHIBITOR SCREEN:

Negative

 

GENERAL FACTOR BETHESDA UNITS:

≤0.4 Bethesda Units

Interpretation

Normally, there is no inhibitor (ie, negative result).

 

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

Cautions

Occasionally, a potent lupus-like anticoagulant may cause false-positive testing for a specific factor inhibitor (eg, factor VIII or IX).

Clinical Reference

1. Hoffman R, Benz Jr EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Elsevier; 2018

2. Chitlur M, Warrier I, Rajpurkar M, et al. Inhibitors in factor IX deficiency a report of the ISTH-SSC international FIX inhibitor registry (1997-2006). Haemophilia. 2009;15(5):1027-1031. doi:10.1111/j.1365-2516.2009.02039.x

Method Description

This assay consists of measuring the difference in factor IX activity (partial thromboplastin time 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 IX value of the normal plasma is adjusted to approximately 20%, because the factor IX 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; 1975:143-145; 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 IX, 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 its factor IX activity is measured and compared to a control run at the same time. The difference between the factor IX activity of the patient's incubation mixture and that of the control is used to calculate the titer. The residual factor IX activity is converted to Bethesda units: 50% residual factor IX is equal to 1 Bethesda unit. Assays using the same basic principle as the Bethesda assay are used to quantitate the inhibitors of other coagulation factors.(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

Report Available

1 to 3 days

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

85390

85250

85335 (if appropriate)

85335 (if appropriate)

85390 (if appropriate)

NY State Approved

Yes

Forms

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