Clinics and Departments

Laboratory Services

Lab Dept:

Coagulation

Test Name:

PTT MIXING STUDIES

General Information

Lab Order Codes:

PTTM

Synonyms:

APTT Mixing Studies; APTT Correction Studies; Mixing Study, PTT; Inhibitor Screen; Differential PTT; PTT Substitution

CPT Codes:

85732 – Thromboplastin time, partial (PTT); substitution, plasma fractions, each

Test Includes:

PTT 1:2 dilution reported in seconds.

Logistics

Test Indications:

Useful for detecting the presence or 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

Specimen Type:

Whole blood

Container:

Light Blue top tube (Buffered Na Citrate 3.2%)

Draw Volume:

2.7 mL blood

Processed Volume:

Minimum: 1 mL plasma

Collection:

● A clean venipuncture is essential.
● Mix thoroughly by gentle inversion.
● Deliver immediately to the laboratory.
● Refrigerate specimen if there is a delay in transport of 30 minutes or more.

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 sample; underfilled tube; mislabeled or unlabeled specimens

Interpretive

Reference Range:

If an inhibitor is present the PTT will not correct into the normal range with pre/post incubation. If the patient is lacking specific coagulation factors the PTT will demonstrate significant correction.

Critical Values:

N/A

Limitations:

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

Methodology:

PTT 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".
1/5/2011: Updated specimen processing information.
8/20/2013: Updated specimen stability information.



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