Factor XII Inactivator; Factor XII Bethesda Titer
11 days
The factor XII inhibitor (Bethesda titer) assay is performed using an activated partial thromboplastin time (aPTT)-based system.6 Serial dilutions are made of patient plasma with veronal buffered saline, then mixed with normal plasma containing close to 100% factor XII activity, and are then incubated for two hours. An aPTT-based factor XII assay using factor XII-depleted plasma substrate is then performed on these incubated mixtures. Results are compared to those of incubated normal plasma. One Bethesda unit is defined as the amount of factor XII inhibitor that neutralized 0.5 IU of factor XII in this system. The number of serial dilutions tested is based on the anticipated level of the inhibitor.
Test Includes
This test includes factor XII activity with reflex to factor XII inhibitor (Bethesda titer) when activity is less than or equal to 40%.
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
Do not draw from an arm with a heparin lock or heparinized catheter.
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This profile measures factor XII activity and reflexes to a measurement of factor XII inhibitor level (Bethesda titer) when the activity level is diminished to 40% or less.
Plasma
2 mL
Blue top (sodium citrate) tube
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.
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio. 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 tubes. 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.
| Temperature | Period |
|---|---|
| Frozen | 28 days |
| Freeze/thaw cycles | Stable x3 |
Factor XII Inactivator; Factor XII Bethesda Titer
11 days
The factor XII inhibitor (Bethesda titer) assay is performed using an activated partial thromboplastin time (aPTT)-based system.6 Serial dilutions are made of patient plasma with veronal buffered saline, then mixed with normal plasma containing close to 100% factor XII activity, and are then incubated for two hours. An aPTT-based factor XII assay using factor XII-depleted plasma substrate is then performed on these incubated mixtures. Results are compared to those of incubated normal plasma. One Bethesda unit is defined as the amount of factor XII inhibitor that neutralized 0.5 IU of factor XII in this system. The number of serial dilutions tested is based on the anticipated level of the inhibitor.
Test Includes
This test includes factor XII activity with reflex to factor XII inhibitor (Bethesda titer) when activity is less than or equal to 40%.
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
Do not draw from an arm with a heparin lock or heparinized catheter.
Accredited Laboratory Partner
Contact Technical Support
This profile measures factor XII activity and reflexes to a measurement of factor XII inhibitor level (Bethesda titer) when the activity level is diminished to 40% or less.
Plasma
2 mL
Blue top (sodium citrate) tube
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.
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio. 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 tubes. 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.
| Temperature | Period |
|---|---|
| Frozen | 28 days |
| Freeze/thaw cycles | Stable x3 |