6,502
edits
Changes
→(A)PTT
===(A)PTT===
===(A)PTT===
The aPTT measures the time necessary to generate fibrin from initiation of the intrinsic pathway (Figure 157.1). Activation of factor XII is accomplished with an external agent (e.g., kaolin) capable of activating factor XII without activating factor VII. Since platelet factors are necessary for the cascade to function normally, the test is performed in the presence of a phospholipid emulsion that takes the place of these factors. The classic partial thromboplastin time depends on contact with a glass tube for activation. Since this is considered a difficult variable to control, the "activated" test uses an external source of activation.
2:The activated partial thromboplastin time (APTT) is also measured by an automated analyzer. The APTT is a
measure of the intrinsic and common coagulation pathways. Like the ACT it will be prolonged by abnormalities or
deficiencies in factors XII, XI, IX, VIII, X, V, II or I. It is not affected by thrombocytopenia. The APTT is considered
a more sensitive test than the ACT and will become prolonged when approximately 70% of a factor is depleted in
comparison the ACT will only be prolonged when approximately 90% of a factor is depleted.
4:The aPTT measures the time necessary to generate fibrin from initiation of the intrinsic pathway (Figure 157.1). Activation of factor XII is accomplished with an external agent (e.g., kaolin) capable of activating factor XII without activating factor VII. Since platelet factors are necessary for the cascade to function normally, the test is performed in the presence of a phospholipid emulsion that takes the place of these factors. The classic partial thromboplastin time depends on contact with a glass tube for activation. Since this is considered a difficult variable to control, the "activated" test uses an external source of activation.
Technique
Technique