Activated partial thromboplastin time (APTT)

APTT measures the time taken to form a clot when selected clotting factors are activated under laboratory conditions. The test is used to investigate coagulation disorders and in selected protocols for monitoring unfractionated heparin. Prolongation may occur with factor deficiencies, inhibitors or medicine effects; significance depends on the clinical situation.

A prolonged APTT does not always mean increased bleeding, and a normal result does not exclude every haemostasis disorder. Treatment is not adjusted on the basis of one value alone. The doctor assesses the result together with symptoms, medical history and other investigations. The reference values of the individual laboratory are used for comparison, and changes over time are considered during follow-up.

• Assess selected parts of coagulation.
• Clarify the causes of abnormal coagulation results.
• Monitor heparin according to the protocol chosen by the doctor.