Prolonged PTT

The initial laboratory evaluation of a patient with symptoms of either bleeding or thrombosis often includes a partial thromboplastin time (PTT) and prothrombin time (PT). Isolated prolonged PTT with a normal PT could indicate a factor deficiency, the presence of an inhibitor of coagulation, or an artifact related to blood sample collection and processing. In this chapter, we review clinical situations associated with the finding of an isolated prolonged PTT, including preanalytical factors that contribute to laboratory artifact, deficiency of the coagulation that encompass the “intrinsic” pathway of coagulation, and coagulation factor inhibitors. Important diagnostic considerations are reviewed, with suggestions related to laboratory evaluation and, in some cases, patient treatment. While anticoagulant drugs may be monitored with the PTT, pharmacologic prolongations of the PTT are not specifically discussed here.