[Reagent-dependent pseudo-prolongation of activated partial thromboplastin time].

We report a case of pseudo-prolongation of activated partial thromboplastin time (APTT), which was suspected to be caused by an animal-derived phospholipid. A 78-year-old woman was referred to our hospital because of an unexplained APTT prolongation. She had compensated alcoholic liver cirrhosis, with modestly decreased platelet count and normal prothrombin time, and no bleeding tendency. The APTT was 66 seconds in a test using phospholipid extracted from rabbit brain but was 34.9 seconds with synthetic phospholipids. The artifactual pseudo-prolongation of the APTT was seemingly attributable to the susceptibility of the test reagents to low factor XII levels. Thus, tests with different APTT reagents would be useful to physicians in the diagnosis of similar cases.