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Lab Dept:
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Coagulation
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Test Name:
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PROTIME AND INR
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General Information
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Lab Order Codes:
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PT
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Synonyms:
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PT; Protime; Prothrombin Time and INR
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CPT Codes:
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85610 - Prothrombin time
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Test Includes:
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PT reported in seconds and INR
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Logistics
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Test Indications:
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Useful for evaluating the extrinsic and common pathways of the coagulation system; aid in screening for congenital deficiencies of factors II, V, VII, and X, dysfibrinogenemia, afibrinogenemia, coumarin effect, liver disease, disseminated intravascular coagulation (DIC), and vitamin K deficiency.
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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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2 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.
● Depending on the patient's hematocrit, up to 3 assays can be determined using one 1.8 mL light blue top tube.
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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 (Buffered Na Citrate 3.2%) tube
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Draw Volume:
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1.8 mL or 2.7 mL blood
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Processed Volume:
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1 mL (Minimum: 0.5 mL) plasma
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Collection:
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● A clean venipuncture is essential.
● Mix thoroughly by gentle inversion.
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Special Processing:
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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:
● 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; mislabeled or unlabeled specimens
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Interpretive
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Reference Range:
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Test
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All ages
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PT:
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8.5 – 12.4 seconds
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INR:
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0.79 – 1.20
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INR Therapeutic Ranges for Oral Anticoagulants
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Prophylactic dose:
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1.4 – 1.9
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Standard dose:
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2.0 – 3.0
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High dose:
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2.5 – 3.5
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Note: Extremely high results will be reported as PT >120.0, INR >9.0
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Critical Values:
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PT: >17.0 seconds
INR: >1.7
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Limitations:
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N/A
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Methodology:
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Placental Thromboplastin
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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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2/17/2005: Critical value for INR previously listed as >1.5.
7/19/2006: Removed statement, "Do not transport by pneumatic tube".
7/25/2006: Added Oral Anticoagulant therapeutic ranges.
1/30/2008: Edited reference ranges: PT previously reported as: 10.6 – 15.5 seconds, critical value previously reported as: >21.2
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