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HelpMayo 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.
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.
Special Instructions
Method Name
F_9, 9BETH, F9_IS: Optical Clot-Based
9INHT: Technical Interpretation
9AINH: Medical Interpretation
Reporting Name
Factor IX 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 |
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 daysSpecimen Retention Time
7 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
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)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| 9INHE | Factor IX Inhib Profile, P | 96459-3 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 9INHT | FIX Inhib Profile Tech Interp | 69049-5 |
| F_9 | Coag Factor IX Assay, P | 3187-2 |