Prothrombin Time (PT) and Partial Thromboplastin Time (PTT)

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.^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 alternate 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.

Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.

Specimens are stable at room temperature for 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 with screw cap (Labcorp No. 49482). Freeze immediately and maintain frozen until tested. Refer to Coagulation Collection Procedures for directions.

Requirements for patients receiving heparin are different: If testing cannot be performed within one hour of collection, frozen plasma must be submitted. Specimens should be centrifuged for at least 15 minutes at 1500xg to produce platelet-poor plasma, and the plasma quick frozen and maintained in this condition until tested.

Gross hemolysis; clotted specimen; frozen specimen thawed in transit; tubes <90% full; improper labeling; specimen collected in tube other than 3.2% citrate; refrigerated sample