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Activated Partial Thromboplastin Time

Alias: APTT (Heparin)

Discipline: Haematology

Test information: The APTT measures the activity of the intrinsic and common factors of the Coagulation pathway.
The term 'thromboplastin' in this test refers to the formation of a complex formed from various plasma clotting factors which converts prothrombin to thrombin and the subsequent formation of the fibrin clot.
It is used alongside the Prothrombin Time (PT) as general screening procedure for clotting abnormalities and for monitoring patients receiving heparin anticoagulant therapy.

Specimen Type(s)
  • Blood;
Other Acceptable Specimen Type(s)
Specimen Container - Adult
  • Royal Blue Top BD;
Specimen Container - Paediatric
  • N/A;
  • N/A;
Part of a test profile?
Volume (min) of sample to be sent to laboratory
Patient Preparation, Sample Handling and Transport
Coagulation samples are volume critical, if a patient is difficult to bleed paediatric tubes (1.3ml) are available on request.
Some patients with a grossly raised Haematocrit (HCT) >0.57 may give erroneous coagulation test results - individual patient adjusted volume coagulation tubes are available on request from the laboratory.
Sample to be tested within 1hr of collection.
Maximum add on time
4 hours
Units and Reference Ranges / Interpretation
1.5 - 2.5 (ratio)
UKAS number
UKAS accredited test?

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Last updated: 03-05-2024