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


Whole blood or plasma


4.5 mL, 2.7 mL, 1.8 mL

Minimum Volume

90% of full draw


Blue-top (sodium citrate) tube


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

Temperature Period
Room Temperature4 hours
RefrigeratedNot recommended
Frozen2 weeks
Freeze/thaw/ cycles Stable x 3

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.