Clinics and Departments

Laboratory Services

Lab Dept:

Coagulation

Test Name:

PTT

General Information

Lab Order Codes:

PTT

Synonyms:

APTT; Partial Thromboplastin Time; Activated PTT

CPT Codes:

85730 – Thromboplastin time, partial (PTT); plasma or whole blood

Test Includes:

PTT reported in seconds.

Logistics

Test Indications:

Useful for screening of the intrinsic and common pathways in the coagulation system (factors II, V, VIII, IX, X, XI and XII); screening for dysfibrinogenemia disseminated intravascular coagulation (DIC), congenital hypofibrinogenemia K deficiency, HMWK deficiency and prekallikrein deficiency.

Lab Testing Sections:

Coagulation

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

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 (Buffered Na Citrate 3.2%) tube

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 uL of deadspace.

Test within:
● Four (4) hours when stored as plasma remaining 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 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:

The following specimens will be rejected: Improper tube, clotted sample, overfilled tube, underfilled tube, mislabeled or unlabeled specimens

Interpretive

Reference Range:

Age

Range (seconds)

0 - 3 months:

25.0 - 43.6

3 – 6 months:

23.2 - 40.1

>6 months:

20.0 - 34.4

Note: Extremely high values will be reported as PTT >120.0 seconds.

Critical Values:

>48 seconds

Limitations:

It is recommended that this test not be used to monitor heparin therapy at Children's Hospitals and Clinics due to the variation in response between individuals. This is caused by different plasma levels of heparin neutralizing proteins and age-related variations in levels of intrinsic pathway factors. The PTT may be in the normal range in patients with mild factor deficiencies, especially Factor IX.

Methodology:

Micronized silica

Contraindications:

Patient on heparin therapy

References:

Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis

Updates:

2/17/2005: Critical value previously listed as >51.0 seconds.
7/19/2006: Removed statement, "Do not transport by pneumatic tube".
1/30/2008: 0 - 3 months:1.3 – 54.5 sec, 3 – 6 month: 29.0 – 50.1 sec, >6 months: 25.0 – 43.0 sec, Critical value previously listed as >60 sec.
8/20/2013: Updated specimen stability information.
9/15/2014: Added off campus collection info.



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