title: Artifactual prolongation of the activated partial thromboplastin time mimicking a coagulopathy. A lesson relearned.
abstract: A markedly prolonged activated partial thromboplastin time (APTT) was observed in a 61-year-old woman with bruising and a decreasing hematocrit. Coagulation laboratory evaluation was sought to determine the cause of the prolonged APTT and bleeding. Evaluation demonstrated that, rather than identifying a coagulopathy, the APTT prolongation was most likely artifactual. The APTT was actually very short. With a combination of a relatively strong activating APTT reagent (Dade Actin; Dade, Miami, FL) and a fixed lag phase in the automated coagulation instrument (16 seconds), the clot formed before the instrument began to read. Thus, during the period of observation (120 seconds), no change in optical density was observed. This was interpreted by the laboratory as "> 120 seconds." This case reminds those involved in the performance and interpretation of APTTs of the importance of a manual or visual method of verifying markedly prolonged APTTs.
authors.affiliation: Department of Pathology, University of Virginia Health Sciences Center, Charlottesville 22908.
authors.forename: J E
authors.initials: JE
authors.lastname: Humphries
authors.forename: M N
authors.initials: MN
authors.lastname: Acker
authors.forename: D E
authors.initials: DE
authors.lastname: Schnell
authors.forename: J W
authors.initials: JW
authors.lastname: Knarr
mesh_terms: D016477:Artifacts; D001778:Blood Coagulation Disorders / Q000139:chemically induced / Q000175:diagnosis*; D003288:Contusions / Q000097:blood; D003937:Diagnosis, Differential; D005260:Female; D006470:Hemorrhage / Q000097:blood; D006801:Humans; D008875:Middle Aged; D010314:Partial Thromboplastin Time