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Lab Dept:
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Coagulation
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Test Name:
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PT MIXING STUDIES
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General Information
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Lab Order Codes:
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PTM
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Synonyms:
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Protime Mixing Study; Prothrombin Time Mixing Study; Simple PT Mixing Study
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CPT Codes:
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85611 - Prothrombin time: substitution, plasma fractions, each
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Test Includes:
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PT 1:2 dilution reported in seconds.
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Logistics
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Test Indications:
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Useful for detecting the presence/absence of an inhibitor or the absence of specific coagulation factors.
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Lab Testing Sections:
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Coagulation
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Phone Numbers:
Minneapolis:
Saint Paul:
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612-813-6280
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651-220-6550
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Test Availability:
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Daily, 24 hours
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Turnaround Time:
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4 hours
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Special Instructions:
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● 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.
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Specimen
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Specimen Type:
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Whole blood
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Container:
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Light Blue top tube (Buffered Na Citrate 3.2%)
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Draw Volume:
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2.7 mL blood
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Processed Volume:
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1 mL plasma
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Collection:
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● A clean venipuncture is essential.
● Mix thoroughly by gentle inversion.
● Deliver immediately to the laboratory. Indicate when specimen is drawn from a line or a heparin lock.
● Specimen must arrive within 30 minutes of collection.
● Refrigerate specimen if there is a delay in transport of 30 minutes or more.
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Special Processing:
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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:
● Two (2) hours when stored 22 to 26°C.
● Four (4) hours when stored 2 to 4°C.
● Two (2) weeks when stored -20°C.
● Six (6) months when stored -70°C (rapidly frozen).
● Plasma must be frozen if testing cannot be completed within four (4) hours.
● Frozen plasmas are thawed at 37°C for three (3) minutes, test immediately.
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Patient Preparation:
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None
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Sample Rejection:
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Improper tube, Clotted specimen, Underfilled tubes, Overfilled tubes, Specimen more than 2 hours old, Mislabeled or unlabeled specimens
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Interpretive
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Reference Range:
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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.
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Critical Values:
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N/A
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Limitations:
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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.
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Methodology:
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PT based correction of patient’s plasma with normal plasma.
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Contraindications:
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Current anticoagulant therapy.
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References:
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Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis
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Updates:
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7/19/2006: Removed statement, "Do not transport by pneumatic tube".
12/14/2010: Updated processing information.
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