Full draw; 1.8 mL light blue top (mix well) must be at least 90% full.

Short drawn tube, clot, traumatic tap (excessive hemolysis).

22-31 seconds

Critical value: ≥50 seconds (on outpatients only)

Results called for inpatients only: >79 seconds

Blood from this test cannot be drawn through the IV line in which the heparin is being administered to the patient. A separate venipuncture is required at a different site.

Must be drawn swiftly with a clean venipuncture (no hematoma). Time drawn must be indicated on requisition. Obtain special tube from lab if patient's hematocrit is over 55%. If patient is on heparin therapy, samples must be in the lab within one hour after draw. All other samples must be tested within four hours.

Certain substances, such as propofol, may interfere with aPTT measurement by this method. If aPTT is being used for heparin monitoring, consider ordering Heparin Assay [LAB317]. Contact the clinical laboratory with questions.

Activated Partial Thromboplastin time (aPTT) may be performed on the same collection tube as Prothrombin Time and Fibrinogen.

The current lot of aPTT reagent is consistent with previous lots. The mean of the reference range with this reagent is 27 seconds; the reference range is 22-31 seconds. The mean of the published therapeutic range for heparinization of 1.5-2.5 times the mean of the reference range (27) yields values of 40-67 seconds with this reagent. Based on our studies of heparin responsiveness, this is a reasonable target range to use with this reagent when treating uncomplicated venous thromboembolism.


This test is also performed in the Iowa River Landing (IRL) clinical laboratory (for specimens drawn at that site).

Optical clot detection.