Activated Partial Thromboplastin Time (APTT)
Introduction
Activated
Partial Thromboplastin Time (APPT) is a useful and effective method for
screening patients with a bleeding tendency, for evaluating the effect of
therapy in procoagulant disorders and as the basis for several specific
coagulant factor assay procedures. The APTT has been widely used as a test
for monitoring and regulating heparin therapy. The presence of nonspecific
inhibitors, such as lupus-like anticoagulant, may prolong the APTT. APTT
is also sensitive to decreased concentrations of Fleicher and Fitzgerald
Factors I, II, V, VIII, IX, X, XI and XII.
Indications for Testing
All individuals with
a history of a bleeding disorder, arterial or venous thrombosis, two or
more consecutive pregnancy losses or who are receiving anticoagulant
therapy should be tested for APTT.
Detection Method
In the APTT test a contact
activator is used to stimulate the production of Factor XIIa by providing
a surface for the function of high molecular weight kininogen, kallikrein
and Factor XIIa. This contact activation is allowed to proceed at 37oC for
a specific period of time. Calcium is then added to trigger further
reactions and the time required for clot formation is measured.
Phospholipids are required to form complexes, which activate Factor X and
Prothrombin. APTT is measured by the IL TestTM APTT-SP(liquid).
Interpretation of Test Results
Expected
normal values: 24.3 - 35.0 seconds.
Specimen Collection and Shipping
Requirements
- Collect one (1) blue top tube.
- Spin, separate, freeze and ship in prepaid FedEx mailers overnight,
next day morning.
Turn around Time
Processing of specimens
begins immediately upon receipt at our facilities. Results are routinely
available within 7 to 10 days and are initially faxed, then mailed to the
requesting physician.
Cost
Included in our fees are specimen
collection and shipping materials, all courier and shipping charges,
telephone and written reports, and consultation with physicians. Please
call (312) 274-1928 for pricing information.
Request Hard Copy
References
Van der Velde EA, Poller L. The
APTT monitoring of Heparin. The ISTH/ICSH Collaborative Study. Thromb Haem
1995;73:73-81.
Quick AJ. Hemorrhagic diseases and thrombosis. In: Lea and Febiger,eds.
Philadelphia, 1966.
Kelsey PR, Stevenson KJ, Pollan L. The diagnosis of lupus
anticoagulants by the activated partial thromboplastin time. The central
role of phosphatidylserine. Thromb Haem 1984; 52:172-75.
Brandt IT, Barna LK, Triplett DA. Laboratory identification of lupus
anticoagulants: results of the second international workshop for
identification of lupus anticoagulants. Thromb Haem 1995;74:1597-1603.
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