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| Test Name: | Prothrombin Time (PT/INR ) |
|---|---|
| Test Code: | 005199 |
| Other Names: | N/A |
| Test Includes: | INR, Prothrombin Time |
| Specimen Requirements: | Whole blood or plasma, 4.5 mL |
| Container: | Blue-top (sodium citrate) tube; do NOT open tube unless plasma is to be frozen. |
| Collection Instructions: | Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.(1) Evacuated collection tubes must be filled to completion to ensure a proper blood-to- anticoagulant ratio.(2,3) The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples unless the sample is collected using a winged (butterfly) collection system. With a winged blood collection set a discard tube should be drawn first to account for the dead space of the tubing and prevent under-filling of the evacutated tube.(4,5) When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternative anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested. Print and use the Volume Guide for Caogulation Testing to ensure proper draw volume. |
| Stability: | Specimens are stable at room temperature for up to 24 hours. If testing cannot be completed within 24 hours, specimens should be centrifuged for at least 10 minutes at 1500xg; plasma should then be transferred to a LabCorp PP transpak frozen purple tube w |
| Rejection Criteria / Special Instructions: | Values obtained with different assay methods should not be used interchangeably in serial testing. It is recommended that only one assay method be used consistently to monitor each patient's course of therapy. This procedure does not provide serial monito |
| Methodology: | Prothrombin time reagent containing thromboplastin and calcium chloride is mixed with the patient plasma and the time to clot formation is measured photo-optically. The calcium chloride overcomes the citrate anticoagulant and allows the tissue factor in t |