UCSF Navigation Bar

UCSF Departments of Pathology & Laboratory Medicine Home Page

Lab Manual for UCSF Clinical Laboratories

Lab Manual for SFGH

Internal Resources

Click here for more information about laboratory operations and procedures

If you have additional questions regarding this test, please call: 415-353-1667

Search Our Test Menu

Antithrombin Activity

Item Value
Approval req'd? No
Available Stat? No
Test code AT
Test group Antithrombin
Performed by Parnassus Hematology
Method Chromogenic substrate
Collection Instructions 1. Check the expiration date on the label of the blue top vacutainer before drawing the patient.

2. For blood collection in a sodium citrate blue top, the tube must be filled to above the Minimum Fill Indicator on the tube. It is crucial to wait and allow the tube to stop filling before removing it from the needle.

3. With use of a butterfly needle, draw about 1 cc using a separate blue top to remove air from tubing, discard the first tube and then draw a second blue top tube filled to the full extent of the vacuum.

4. Tubes should not be filled past the Maximum Fill dashed line by either using a syringe or removing the tube cap.

For patients with Hct's ≥ 55% please contact Hematology (x3-1747) to obtain blue top tubes with adjusted citrate volumes in order to maintain the proper citrate to plasma ratio for coagulation studies.
Container type Blue top filled to full extent of vacuum
Amount to Collect 2.7 mL blood
Sample type Citrated plasma
Preferred volume 1 mL plasma
Min. Volume 0.5 mL plasma
UCSF Rejection Criteria Samples collected in outdated blue top vacutainer. Over-filled or under-filled tubes may be rejected
Processing notes Deliver sample to Hematology asap for processing. Test specimens within four hours of collection or freeze plasma in a plastic tubes at -20C.
Units % activity
Normal range
0-3 months Not established (See Additional Information)
Adult (> 3 mo.) 79-120%
Synonyms ATIII; AT3; AT III; AT Activity; Anithrombin III Activity
Turn around times 1-2 weeks.
Additional information There is no published pediatric reference range for Antithrombin activity, which generally parallels the level of antigen. The following table gives age-adjusted reference ranges for Antithrombin antigen:

Day 1 Day 5 Day 30 Day 90
39-87% 41-93% 48-108% 73-121%


Reference: Andrew M. Et al. Development of the Human Coagulation System in the Full Term Infant. Blood July 1987, 70(1):165-172.

A low level of antithrombin may be associated with an inherited deficiency or with secondary causes such as acute venous thrombosis, liver disease, disseminated intravascular coagulation, heparin therapy, pregnancy, estrogen therapy, and nephropathy with proteinuria.

If unusual findings are noted a pathologist review and interpretation may be performed and separately billed for
LOINC code 27811-9
Last Updated 4/1/2014 11:37:49 AM
Entry Number 65
UCSF home page UCSF home page About UCSF Search UCSF UCSF Medical Center