Activated Partial Thromboplastin Time (aPTT)

Label Mnemonic:	PTT
Epic code:	LAB1117
Order form:	Laboratory Requisition
Supply order:	Supply Order Form
Billing:	Billing Policies
CPT code:	85730

Specimen(s):

Plasma More information

Collection Medium:

Light Blue top tube 1.8 mL (Na Citrate)

Minimum:

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

Rejection Criteria:

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

Testing Schedule:

24 hrs/day, 7 days a week, including holidays.

Turn Around Time:

1 hour (upon receipt in laboratory)

Reference Range:

22-31 seconds

Critical value: ≥50 seconds (on outpatients only)

Results called for inpatients only: >79 seconds

Comments:

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.

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

Please print, complete and submit the Advance Beneficiary Notice (ABN) along with the Laboratory Requisition before shipping the specimen.

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.

Methodology:

Optical clot detection.

Sample Processing:

Double-centrifuge specimen to prepare platelet-free plasma.
Immediately centrifuge specimen at 3500 RPM for 12 minutes.
Using a plastic transfer pipette, carefully remove plasma from cells avoiding the platelet/buffy coat.
Place plasma into a labeled plastic tube.
Centrifuge plasma again at 3500 RPM for 12 minutes.
Remove the top of the plasma and place into a labeled plastic tube.
Freeze double-spun plasma within 4 hours of collection time at -20 degrees C or below.

Sample Storage:

Freeze plasma immediately.

Transport Instructions:

Place labeled specimen into zip-lock type biohazard bag; seal bag.
Place requisition into outside pocket of bag.
Place dry ice on top of specimen in Styrofoam container.
Samples received thawed will be cancelled.