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Laboratory Medicine

Test catalogue

Activated Partial Thromboplastin Time (aPTT)

Test name

Activated Partial Thromboplastin Time (aPTT)

Blue top Specimen Type / Requirements

Container Type = Blue (Sodium Citrate)

Minimum Volume = Full draw

9:1 Ratio (9 parts blood to 1 part anticoagulant)

Specimen Handling

Collection Instructions: Ensure both sample and requisition are labelled properly. Must indicate anticoagulant status to avoid delay. Write your initials, date and time of collection on the collection label.

Transportation: In/Outpatients: Send whole citrated blood at room temperature as soon as possible. Referred-in: Send frozen citrated plasma on dry ice. All samples must be sent to the Core Laboratory.

Stability: Specimens are stable for 4 hours post collection at room temperature. Specimens which are not tested within 4 hours can be double-spun to remove the citrated plasma. The citrated plasma is stable at -20°C for up to two weeks or -70°C for up to six months.

Sample Rejection Criteria: Clotted sample, grossly hemolyzed samples, Unlabeled or samples with insufficient quantity will be rejected.

Required Documentation

Turnaround Time (TAT)

STAT: 45 min

Routine: 4 hrs

Test Utilization

Reference Value


24.0 - 37.0 seconds

Therapeutic range: 61.0 – 95.0 seconds

Pediatric (< 3 months):

25.0 - 45.0 seconds

Critical Values

150.0 seconds

Test Code



Clotting Assay

Testing Location

SMH-Routine Coagulation

Other Information

Last Updated: June 06, 2019