Activated Partial Thromboplastin Time (APTT)
Indications to perform this test:  The APTT is performed in cases of suspected bleeding disorders.  This test specifically evaluates the common and  intrinsic clotting pathway.  The extrinsic pathway is evaluated through the OSPT.

 

Coagulopathies and Hepatic Disease:  The clotting factors are acute phase reactant proteins that are manufactured in the liver.  In cases of hepatic disease, it is not uncommon to see coagulopathies as a result.  Therefore, it is advisable to include clotting tests in your diagnostic workup of any case of suspected hepatic disease, especially if you are considering any invasive procedures like biopsies or fine needle aspirates.


The Test:  The patient's plasma is mixed with partial thromboplastin which is usually a rabbit brain extract which mimics the effect of platelet phospholipid.  The particulate activator may be diatomaceous earth, kaolin, celite, ellagic acid, or micronized silica.  Because different commercial kits contain different reagents, the clotting times will vary depending on the components.  The APTT will be prolonged with any deficiency of the intrinsic or common clotting factors, or in the presence of inhibitors.

Plasma and Partial Thromboplastin + particulate activator + CaCl2 whole blood clot

 

Interpretation of APTT results:

  • Normal OSPT and prolonged APPT = defect in the intrinsic pathway
  • Normal APPT and prolonged OSPT = defect in the extrinsic pathway
  • Prolonged APPT and OSPT = multiple defects or defect in the common pathway


For  more information . . .