Synonyms: PTT
Related tests: PT, LAC
Clinical significance
The partial thromboplastin time is the time it takes for a fibrin clot to form after calcium ions and a phospholipid reagent are added.
The PTT measures the intrinsic pathway (factors XII, XI, IX and VIII) and the common pathway (factors V, II, X) of coagulation. A prolonged PTT is caused by clotting factor deficiencies (haemophilia A and B, von Willebrand disease), disseminated intravascular coagulation (DIC), antiphospholipid syndrome (APS), liver failure (through reduced synthesis), biliary obstruction, malabsorption and coumarin anticoagulant therapy (through vitamin K deficiency), and heparin therapy.
Clinical indications
Clotting factor deficiencies (XII, XI, X, IX, VIII, V, II), DIC, hepatobiliary failure, malabsorption, monitoring of heparin therapy.
Sample type
The patient must have a blood sample taken.
Preparation
You must fast for at least 8 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes.
Notes
Lupus anticoagulant (LAC) prolongs the PTT not because of a clotting factor deficiency but because of an antibody acting against phospholipid antigens.