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Test Code PTT Activated Partial Prothrombin Time

Important Note

Direct oral anticoagulants (non-vitamin K) should not be monitored with this assay.

Heparin therapy specimens must be centrifuge and perform within 1 hour of collection.

Tube must be properly filled.

Additional Codes

Cerner

NextGen

APTT

PTT

PTT

 

Alternate Name(s)

APTT

PTT

Useful For

The Activated Partial Thromoplastin Time (APTT) is a basic coagulation screening test for the activity of the intrinsic pathway factors XII, XI, IX, VIII, X, V, II, and fibrinogen.  Prolonged APTT may be seen in the following situations:

  • Congenital Deficiencies:
    • If PT is normal, factors VIII, IX, XI, XII may be deficient.
    • If these factors are normal, there may be a prekallikrein or HMW kininogen deficiency.
  • Acquired Deficiencies:
    • Liver diseases
    • Consumptive coagulopathy
    • Fibrinolysis
    • Circulating anticoagulants
    • During heparin or oral anticoagulant therapy
    • Treatments with thrombin inhibitors

Methodology

The STA® - Compact Max® is a fully automated coagulation instrument, which uses an electromagnetic mechanical clot detection system. The APTT test measures the time of clot formation after plasma is re-calcified in the presence of a standardized amount of platelet substitute (cephalin) and a particulate activator (silica). The oscillation of a steel ball within the cuvette containing the reagent and patient plasma is monitored by the STA® - Compact Max®.  When the oscillation of the steel ball is slowed by clot formation, the sensor determines the time in seconds.

Patient Preparation

None

Collection Instructions

  • Sample collections must comply with the recommendations for hemostasis tests.
  • 3.2% sodium citrate tubes only.
  • Tube must be properly filled.

Specimen Requirements

Preferred Volume

1 mL plasma

Minimum Volume

1 mL plasma

Container

3.2% sodium citrate tube (blue top), BD or Greiner Vacutainer tubes

Stability
  • Un-heparinized specimens:
    • Uncentrifuged specimens: Do not refrigerate. Stable for 4 hours at 18-24⁰;
    • Centrifuged and separated plasma: Stable for 4 hours at 18-24⁰ C or 2-8⁰ C.
  • Heparin therapy specimens:
    • Centrifuge and perform within 1 hour of collection.
  • Platelet poor plasma is stable for 2 weeks at -20⁰ C. Specimens must be double-spun and separated prior to freezing.

Rejection Criteria
  • Clotted specimens
  • PTT results < 20.0 seconds
  • Hemolyzed
  • Expired collection tube
  • Under or Overfilled tube (blood/anticoagulant ratio must be 9:1; tube filled between 90-110 %)
  • Heparinized specimens not centrifuged within 1 hour of collection.
  • Improperly mixed specimen    

Result Reporting and Reference Values

Reference Range

24.3-35.2 seconds

Critical Ranges

≥ 80.0 seconds

Reflex Testing

None

Limitations

When monitoring heparin therapy, any release of platelet factor 4 (PF4), which is a potent inhibitor of heparin, represents a major source of error. Do not collect specimen in glass which may cause this release. Collect only in approved tubes (refer to Specimen Requirements section) and centrifuge within 1 hour of collection.