aPTT

Clinical Significance

Partial Thromboplastin Time, Activated - The aPTT is a screening test that will detect deficiencies or inhibitors to the intrinsic (Factors VIII, IX, XI and XII) and common (Factors II, V, X and fibrinogen) pathway coagulation factors.

Test Details

Methodology

Photo-Optical Clot Detection

Reference Range(s)

≤6 months

Not established

>6 months

23-32 sec


Flagging not provided. Pediatric reference intervals have not been established. Based on published literature, the adult reference interval (23-32 seconds) is generally applicable down to approximately 6 months of age with younger patients having a slightly higher upper limit by several seconds.

Alternative Name(s)

APTT, PTT

Preferred Specimen(s)

One full unopened 3.2% sodium citrate (light blue-top) tube

Alternative Specimen(s)

1 mL frozen plasma

Minimum Volume

0.3 mL

Collection Instructions

Unopened light blue-top tube: Correct ratio of blood to citrate is critical. Do not overfill or underfill collection tube. Mix by inversion 4 times. For non-heparinized patients, maintain specimen at room temperature. Do not uncap. Stable 24 hours at room temperature.

Platelet-poor plasma: Centrifuge light blue-top tube 15 minutes at approximately 1500 g within 60 minutes of collection. Using a plastic pipette, remove plasma, taking care to avoid the WBC/platelet buffy layer and place into a plastic vial. Centrifuge a second time and transfer platelet-poor plasma into a new plastic vial. Plasma must be free of platelets (<10,000/mcl). Freeze immediately and ship on dry ice.

Whole blood: The tubes should be at 100% +/- 10% fill volume in order to obtain the correct ratio.

Transport Container

3.2% sodium citrate (light blue-top) tube

Transport Temperature

Room temperature


Specimen Stability

Reject Criteria

Gross hemolysis • Grossly lipemic • Improper blood to citrate ratio • Clotted • High hematocrits • Thawed plasma received room temperature or refrigerated

Setup Schedule

Set up: Mon-Sat (All shifts); Sun (STAT only); Report available: 1 day