Test Details
Methodology
The patient plasma is mixed with heparin and thrombin. The extent of thrombin inhibition is proportional to the AT concentration of the patient sample. Residual thrombin activity is measured as the rate of conversion of a chromogenic substrate and is used to calculate AT concentration.
Result Turnaround Time
2 - 3 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.
Use
This test is used for confirmation and characterization of acquired or congenital AT deficiency.
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.
Limitations
AT testing should not be performed on patients on unfractionated heparin therapy because heparin decreases plasma AT levels.6,7 AT results for individuals on warfarin therapy should be interpreted with caution because warfarin can increase levels of AT of patients with heterozygous deficiency into the normal range.7 Thrombin inhibitors, such as dabigatran, hirudin, and argatroban, will not interfere with the assay unless it is based on inhibition of thrombin. Direct Xa inhibitor anticoagulants will interfere with the AT activity assay when it is Xa based, falsely elevating the result, possibly masking a deficiency.6
Custom Additional Information
See Antithrombin (AT) Deficiency Profile [015594] for more clinical information.
Specimen Requirements
Specimen
Plasma, frozen
Volume
1 mL
Container
Blue-top (sodium citrate) tube
Collection Instructions
Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio.2,3 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.4,5 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 |
Storage Instructions
Freeze.
Patient Preparation
Do not draw from an arm with a heparin lock or heparinized catheter. Patients ideally should not be on unfractionated heparin or direct Xa inhibitor anticoagulant therapy.
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
Footnotes
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 015040 | Antithrombin Activity | 27811-9 | 015040 | Antithrombin Activity | % | 27811-9 |
| Order Code | 015040 | |||||
| Order Code Name | Antithrombin Activity | |||||
| Order Loinc | 27811-9 | |||||
| Result Code | 015040 | |||||
| Result Code Name | Antithrombin Activity | |||||
| UofM | % | |||||
| Result LOINC | 27811-9 |