Lab Dept:


Test Name:

Antithrombin III, Chromogenic (FAIRVIEW)

General Information

Lab Order Codes:

AT3 (Back-up only)


ATIII; AT3; ATIII, functional; Anti - Thrombin III

CPT Codes:

85300 – Clotting inhibitors or anticoagulants; antithrombin III activity

Test Includes:

Antithrombin III Chromogenic activity reported as a %.


Test Indications:

Antithrombin inactivates thrombin and other serine proteases (activated Factors 12, 11, 10 and 9). In the of absence heparin, this process is relatively slow. In the presence of heparin, antithrombin almost instantaneously inactivates thrombin.

Lab Testing Section:

Coagulation - Sendouts

Referred to:

Fairview University Medical Center (Fairview/Atlas test: ANTCH)

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

Test is performed Mon-Fri: 0700-1300, Sat: 1000-1330. Turnaround is 4 – 8 hours if received during the listed regular working hours. For urgent testing after hours, call Children’s laboratory and they will contact the Fairview tech on call. With pre-notification, stats are done within 1 hour after receipt in the laboratory.

Special Instructions:

Deliver immediately to the laboratory. Indicate on request form when specimen is drawn from a line or a heparin lock.

Specimen must arrive at Fairview University within 24 hours of draw.


Specimen Type:

Whole blood


Light Blue top (Buffered Na Citrate 3.2%) tube

Draw Volume:

2.7 mL blood (in 3 mL tube) Minimum: 1.8 mL blood in a 2 mL tube

Processed Volume:

Specimens will be processed at reference lab facility if received within 4 hours of collection. Otherwise, specimens need to be processed at referring facility and provide minimum of two 0.5 mL specimens frozen at -70. Follow directions below under Special Processing.


A clean venipuncture is essential. If the patient has a coagulation abnormality, apply direct pressure to the puncture site for 10 minutes; apply pressure dressing. Instruct the patient to leave the bandage on for 12 hours.

Mix specimen thoroughly by gentle inversion.

Patient’s with a hematocrit level >55% must have a special tube made to adjust for the hematocrit; contact laboratory for special tube.

Indicate when specimen is drawn from a line or heparin lock.


Special Processing:

Lab Staff: Do Not centrifuge. Do Not freeze. Send to reference lab in original Vacutainer® at room temperature if within 4 hours of collection. Forward promptly.

If specimen is >4 hours old prior to shipment, process specimen as follows:
Spin sample collected in blue top tube(s) for 5 minutes on the Stat Spin centrifuge, remove plasma and transfer to a 4 mL BCS sample cup(s), spin remaining plasma again for 5 minutes in the Stat Spin Centrifuge. Transfer plasma into two labeled 10x75 mL plastic tubes with a minimum of 0.5 mL in each. Freeze at -70 and send specimens on dry ice to Fairview University.

Patient Preparation:


Sample Rejection:

Improper tube; clotted sample; underfilled tubes; overfilled tubes; mislabeled or unlabeled specimens


Reference Range:


Range (%):

0 days:

42 - 80

1 day:

51 - 75

5 days:

54 - 80

30 days:

63 - 93

90 days:

85 - 109

180 days:

94 - 114

1 year:

85 - 135

Critical Values:



If specimen contains heparin (drawn after heparin flush or after receiving heparin), results may be erroneous.


Chromogenic (synthetic substrate) activity assay


Fairview University Laboratory Web Page February 2014


5/20/04: As of March 1, 2004 Fairview University no longer automatically performs the antigenic portion of this test. If this is desired, it needs to be ordered separately with a specific clinical reason. Please contact the laboratory for more information.
References to the antigenic portion of this test have been removed from this procedure.
Specimen volume changed from 4.5 mL to 2.7 mL.
3/26/2008: Removed statement, do not tube through pneumatic tube system.
6/14/2011: Updated reference ranges. Previously listed as ≥1 Year Activity: 80 – 120%.
2/24/2014: Specimen processing update.
3/24/2014: Reference range update.