Sign in →

Test Code PTT Activated Partial Thromboplastin Time (APTT), LAB325


Clot Based Assay

Performing Laboratory

St. Luke's Hospital Cedar Rapids

Specimen Requirements


Preferred: Full blue-top (sodium citrate) 1.8 mL tube-Hemolyzed or short draw specimen is not acceptable.
Specimen Volume:
 0.5 mL sodium citrate plasma

Stability: Centrifuged specimens at 2-4°C or at 18-24°C must be tested within 4 hours of specimen collection.

Collection Instructions: Centrifuge immediately after draw. Forward promptly. If there is a delay in transport of >4 hours or if mailing time exceeds 4 hours, spin down, remove plasma from cells and freeze immediately in plastic vial. Send specimen frozen. Specimen stability is ≤2 weeks when frozen at -20° C.


NOTE:  Patients with a hematocrit of >55% must be recollected using an altered amount of sodium citrate.

Reference Values

These values are for non-heparinized patients:

Screen: 22.5-32.5 seconds
Critical value: >50.0 seconds

Day(s) Test Set Up

Monday through Sunday

Test Classification and CPT Coding


Useful For

The activated partial thromboplastin time test is sensitive to all coagulation factors except factors VII and XIII, so it is an effective screening test for the entire intrinsic coagulation system.