Clinics and Departments

Laboratory Services

Lab Dept:

Coagulation

Test Name:

THROMBIN TIME

General Information

Lab Order Codes:

TT

Synonyms:

Fibrin Time; Fibrinogen screen, Thrombin Time, TT

CPT Codes:

85670 – Thrombin Time, plasma

Test Includes:

Thrombin Time reported in seconds.

Logistics

Test Indications:

Useful at some institutions for monitoring heparin therapy or aiding in the diagnosis of disseminated intravascular coagulation (DIC), fibrinolysis, and the presence of inhibitors.

Lab Testing Sections:

Coagulation

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6551

Test Availability:

Daily, 24 hours

Turnaround Time:

2 hours

Special Instructions:

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

● Depending on the patient's hematocrit, up to 3 assays can be determined using one 1.8 mL light blue top tube.

Specimen

Specimen Type:

Whole blood

Container:

Light Blue top tube (Buffered Na Citrate 3.2%)

Draw Volume:

1.8 mL or 2.7 mL blood

Processed Volume:

0.9 mL (Minimum: 0.5 mL) plasma

Collection:

● A clean venipuncture is essential, avoid foaming.
● Entire sample must be collected with single collection, pooling of sample is unacceptable.
● Capillary collection is unacceptable.
● Patient’s with a hematocrit level >55% must have a special tube made to adjust for the hematocrit; contact lab for a special tube.
● Mix thoroughly by gentle inversion. Deliver immediately to the laboratory at room temperature via courier or pneumatic tube.

Off campus collections:


● Must be tested within 4 hours.
● Do not refrigerate.
● If not received in our lab within 4 hours of collection, sample must be centrifuged and *platelet-poor plasma removed from cells and transferred to an aliquot tube. Freeze at -20C and deliver to the lab on dry ice within 2 weeks.
*Validation of your lab’s centrifuge for platelet poor plasma is required.

Special Processing:

Lab staff: Centrifuge in Stat Spin for 5 minutes or 10 minutes at 3000 rpm at room temperature. For primary tube testing, leave plasma on cells OR remove plasma and place in a 4 mL plastic cup; allow for 100 mL of deadspace.

Test within:
● Four (4) hours when stored in the capped tube above the packed cells 18 to 24C.
● Four (4) hours as plasma that has been separated from cells by centrifugation when stored 2 to 8C or 18 to 24C.
● Two (2) weeks when stored -20C.
● Six (6) months when stored -70C (rapidly frozen).
● Plasma must be frozen if testing cannot be completed within four (4) hours.
● Frozen plasmas are thawed at 37C for three (3) minutes, test immediately.

Patient Preparation:

None

Sample Rejection:

Improper tube; clotted samples; overfilled tubes; underfilled tubes, mislabeled or unlabeled specimens

Interpretive

Reference Range:

<20 seconds

Critical Values:

>25 seconds

Limitations:

Affected by concentration and reactivity of fibrinogen, increased amounts of fibrin degradation products (FDP), and the presence of inhibitory substances, such as heparin and large amounts of fibrin degradation products. Use of this test to monitor heparin will be unreliable if hypofibrinogenemia is present or if fibrin breakdown products (FDP) have been generated by a process of DIC.

Methodology:

Clotting measured photo-optically after addition of exogenous thrombin

Contraindications:

Patients on heparin therapy

References:

Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis

Updates:

7/19/2006: Removed statement "Do not transport through pneumatic tube".
8/20/2013: Updated specimen stability information.
9/15/2014: Addition of off campus collection info.



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