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Partial Thromboplastin Time (PTT)

Partial Thromboplastin Time (PTT) CPT: 85730

Special Instructions

This test is for screening purposes only; it should not be used for therapeutic unfractionated heparin monitoring. Please refer to test Heparin Anti-Xa [117101]. If the patient’s hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted. Refer to Coagulation Collection Procedures for directions.

Expected Turnaround Time

Within 1 day

Specimen Requirements

Specimen

Whole blood or plasma

Volume

4.5 mL, 2.7 mL, 1.8 mL

Minimum Volume

90% of full draw

Container

Blue-top (sodium citrate) tube

Collection

Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate. Evacuated collection tubes must be filled to completion to ensure a proper blood-to-anticoagulant ratio. 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 evacuated 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.

Storage Instructions

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 PP transpak frozen purple tube with screw cap. 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.

Patient Information

As part of an investigation of a possible bleeding disorder or blood clot (thrombotic episode); to help investigate recurrent miscarriages or diagnose antiphospholipid syndrome (APS); as needed to monitor unfractionated (standard) heparin anticoagulant therapy; as indicated as part of an evaluation before surgery or other invasive procedure.

When you have unexplained bleeding, inappropriate blood clotting, or recurrent miscarriages; sometimes when you are on standard heparin anticoagulant therapy; sometimes before a scheduled surgery.

A blood sample drawn by needle from a vein in your arm.

None; however, a high-fat meal prior to the blood draw may interfere with the test and should be avoided.