Clinics and Departments

Laboratory Services

Lab Dept:

Coagulation

Test Name:

PT MIXING STUDIES

General Information

Lab Order Codes:

PTM

Synonyms:

Protime Mixing Study; Prothrombin Time Mixing Study; Simple PT Mixing Study

CPT Codes:

85611 - Prothrombin time: substitution, plasma fractions, each

Test Includes:

PT 1:2 dilution reported in seconds.

Logistics

Test Indications:

Useful for detecting the presence/absence of an inhibitor or the absence of specific coagulation factors.

Lab Testing Sections:

Coagulation

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

4 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.
● Specimen must arrive within 30 minutes of collection.
● Indicate when specimen is drawn from a line or a heparin lock.

Specimen

Specimen Type:

Whole blood

Container:

Light Blue top tube (Buffered Na Citrate 3.2%)

Draw Volume:

2.7 mL blood

Processed Volume:

1 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 being careful not to disturb the cell layer. Centrifuge the plasma a second time and transfer into a clean aliquot tube being careful not to include any residual platelets on the bottom of the 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: Spin sample collected in blue top tube for 5 minutes on the Stat Spin centrifuge, remove plasma and transfer to a 4 mL BCS sample cup. Spin remaining plasma again for 5 minutes in the Stat Spin Centrifuge. Transfer plasma to a new BCS sample cup for analysis leaving approximately 200 uL in the bottom of the original cup to discard.

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 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 specimen, Underfilled tubes, Overfilled tubes, Specimen more than 2 hours old, Mislabeled or unlabeled specimens

Interpretive

Reference Range:

If an inhibitor is present the PT will not correct into the normal range. If the patient is lacking specific coagulation factors the PT will demonstrate significant correction.

Critical Values:

N/A

Limitations:

Correction reactions may be difficult if the patient’s PT is only modestly prolonged. Samples drawn through line or heparin lock will not correct giving the impression of an inhibitor.

Methodology:

PT based correction of patient’s plasma with normal plasma.

Contraindications:

Current anticoagulant therapy.

References:

Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis

Updates:

7/19/2006: Removed statement, "Do not transport by pneumatic tube".
12/14/2010: Updated processing information.
8/19/2013: Updated specimen stability information.
9/15/2014: Added Off Campus collection info.



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