Activated Partial Thromboplastin Time (APTT)

Measures the effectiveness of the INTRINSIC SYSTEM and COMMON PATHWAY. The time for fibrin formation is measured on recalcification of plasma under conditions where the contact activation reactions are optimised. Kaolin is used as a surface activator and platelet substitute is used as a source of phospholipid. The test is performed at 37°C.
The patient APTT is then compared to that of a normal or control plasma which is tested at the same time.
The normal APTT may vary between laboratories, instrumentation and materials used. A suggested normal APTT is 38 - 45s.