Implications of deranged activated partial thromboplastin time for anaesthesia and surgery.

Bleeding during and after surgery ranges from trivial to fatal. Bleeding is in part determined by the patient's coagulation status. The UK National Institute for Health and Care Excellence recommends a pre-operative clotting test for patients with a history of abnormal bleeding. Anaesthetists are familiar with the prothrombin time assay, used to monitor warfarin effect, but anaesthetists may be less familiar with the activated partial thromboplastin time (APTT), which tests the function of the 'intrinsic' clotting pathway. The activated partial thromboplastin time may be prolonged due to contamination, anticoagulant therapy, clotting factor deficiencies, lupus anticoagulant or acquired inhibitors of specific clotting factors. A prolonged activated partial thromboplastin time should lead to: further testing to exclude heparin contamination or therapy, mixing studies to identify factor deficiencies and if necessary dynamic studies, such as the dilute Russell's viper venom time and the Actin FS-activated partial thromboplastin time, to identify direct factor inhibitors. These tests identify abnormalities and their implications for bleeding, helping anaesthetists and haematologists to manage haemostasis for individual patients.