Test Details
Methodology
See individual activity test information for method information. The Bethesda titer measures the amount (titer) of an inhibitor antibody against a specific clotting factor.1 The test uses dilutions of the patient's plasma and determines the amount of antibody needed to neutralize 50% of the factor activity provided by pooled normal plasma with results expressed in Bethesda units (BUs). One Bethesda Unit (BU) is defined as the amount of an inhibitor that will neutralize 50% of one unit of the factor in normal plasma after 120 minutes incubation at 37°C. A higher titer indicates a stronger inhibitor, which can significantly impact treatment. A Bethesda titer assay is not performed when factor level exceeds 40% (i.e., in the absence of measurable factor activity inhibition).
Result Turnaround Time
5 - 7 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Test Includes
This test includes factor IX Activity with reflex to factor IX inhibitor (Bethesda titer) when activity is less than or equal to 40%.
Use
This profile measures factor IX activity and reflexes to a measurement of factor IX inhibitor level (Bethesda titer) when the activity level is diminished to 40% or less.
Special Instructions
If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted. Refer to Coagulation Collection Procedures for directions.
Specimen Requirements
Specimen
Plasma, frozen
Volume
2.0 mL
Minimum Volume
1.0 mL (Note: This volume does not allow for repeat testing.)
Container
Blue-top (sodium citrate) tube
Collection Instructions
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.2 Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio.3,4 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. With a winged blood collection set a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacuated tube.5,6 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternative anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
Stability Requirements
| Temperature | Period |
| Frozen | 28 days |
| Freeze/thaw cycles | Stable x3 |
Reference Range
| Age | Range |
| 1 d | 35–56% |
| 3 d | 44–97% |
| 1 to 11 m | 43–121% |
| 1 to 5 y | 44–127% |
| 6 to 10 y | 48–145% |
| 11 to 16 y | 64–216% |
| >16 y | 59–143% |
Storage Instructions
Freeze.
Patient Preparation
Ideally, the patient should not be on anticoagulant therapy. Avoid warfarin (Coumadin®) therapy for two weeks prior to the test and heparin, direct Xa and thrombin inhibitor therapies for about three days prior to testing. Do not draw from an arm with a heparin lock or heparinized catheter.
Causes for Rejection
Severe hemolysis; improper labeling; clotted specimen; specimen diluted with IV fluids; samples thawed in transit; improper sample type; sample out of stability
References
Collins PW, Chalmers E, Hart DP, et al. Diagnosis and treatment of factor VIII and IX inhibitors in congenital haemophilia: (4th edition). UK Haemophilia Centre Doctors Organization. Br J Haematol. 2013 Jan;160(2):153-170. PubMed 23157203
Scott DW. Inhibitors - cellular aspects and novel approaches for tolerance. Haemophilia. 2014 May;20 Suppl 4(0 4):80-86. PubMed 24762281
Soucie JM, Miller CH, Kelly FM, et al. National surveillance for hemophilia inhibitors in the United States: Summary report of an expert meeting. Am J Hematol. 2014 Jun;89(6):621-625. PubMed 24616187
Footnotes
1. Sang Medicine. Inhibitor Assays in Haemostasis. Practical-Haemostasis website: https://practical-haemostasis.com/Inhibitor%20Assays/inhibitor_assays.html. Updated January 21, 2025. Accessed October 18, 2025.
2. Adcock DM, Kressin DC, Marlar RA. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol. 1997 Jan;107(1):105-110. PubMed 8980376
3. Reneke J, Etzell J, Leslie S, Ng VL, Gottfried EL. Prolonged prothrombin time and activated partial thromboplastin time due to underfilled specimen tubes with 109 mmol/L (3.2%) citrate anticoagulant. Am J Clin Pathol. 1998 Jun;109(6):754-757. PubMed 9620035
4. Clinical Laboratory Standards Institute (CLSI). Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays. 6th ed. CLSI guideline H21. Clinical and Laboratory Standards Institute; 2024.
5. McGlasson DL, More L, Best HA, Norris WL, Doe RH, Ray H. Drawing specimens for coagulation testing: Is a second tube necessary? Clin Lab Sci. 1999 May-Jun;12(3):137-139. PubMed 10539100
6. Gottfried EL, Adachi MM. Prothrombin time and activated partial thromboplastin time can be performed on the first tube. Am J Clin Pathol. 1997 Jun;107(6):681-683. PubMed 9169665
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 086300 | Factor IX Act rflx Inhibitor | 3187-2 | 086298 | Factor IX Activity | % | 3187-2 |
| Order Code | 086300 | |||||
| Order Code Name | Factor IX Act rflx Inhibitor | |||||
| Order Loinc | 3187-2 | |||||
| Result Code | 086298 | |||||
| Result Code Name | Factor IX Activity | |||||
| UofM | % | |||||
| Result LOINC | 3187-2 |
| Order Code | Order Name | Result Code | Result Name | UofM | Result LOINC | |
|---|---|---|---|---|---|---|
| Reflex 1 | 086299 | Factor IX Inhibitor | 086299 | Factor IX Inhibitor | BU | 3185-6 |
| Reflex 1 | ||||||
| Order Code | 086299 | |||||
| Order Name | Factor IX Inhibitor | |||||
| Result Code | 086299 | |||||
| Result Name | Factor IX Inhibitor | |||||
| UofM | BU | |||||
| Result LOINC | 3185-6 | |||||
| Order Code | Order Name | Result Code | Result Name | UofM | Result LOINC | |
|---|---|---|---|---|---|---|
| Reflex 1 | 086011 | Reflex Information | 086011 | Reflex Information | 77202-0 | |
| Reflex 1 | ||||||
| Order Code | 086011 | |||||
| Order Name | Reflex Information | |||||
| Result Code | 086011 | |||||
| Result Name | Reflex Information | |||||
| UofM | ||||||
| Result LOINC | 77202-0 | |||||