title: Lupus anticoagulant increases activated partial thromboplastin time (PTT) prolongation in incubated 1:1 mix.
abstract: Our study analyzes the effects of incubation time and strength of lupus anticoagulant (LAC) on clotting times and prolongation of activated partial thromboplastin time (PTT) 1:1 mix assays with incubation. The prolongation in seconds of PTT 1:1 mix after incubation in the confirmed presence or absence of LAC was correlated to strength of the LAC as well as length of incubation (1 vs. 2 hours). Our study suggests that when screening for possible Factor VIII (FVIII) inhibitors, a 2 hour incubation of a PTT 1:1 mix increases the frequency of false positives as compared to 1 hour incubation, and that most of these false positives are due to LACs. Prolongation of clotting times for PTT 1:1 mixes in patients with LAC is influenced by both length of incubation time and strength of the LAC.
  
  
  CONCLUSIONS
  When using PTT 1:1 mixes to screen for FVIII inhibitors, the effect of a possible LAC on the interpretation of the PTT prolongation should be considered. This effect is influenced by both incubation time and LAC strength.
authors.affiliation: University of Washington Laboratory Medicine, Seattle, WA, USA.
authors.forename: Grace
authors.initials: G
authors.lastname: Monis
authors.forename: Chris
authors.initials: C
authors.lastname: Ferrell
authors.forename: Morayma
authors.initials: M
authors.lastname: Reyes
mesh_terms: D001528:Behcet Syndrome / Q000097:blood*; D001777:Blood Coagulation / Q000502:physiology*; D006405:Hematology / Q000379:methods*; D006801:Humans; D016682:Lupus Coagulation Inhibitor / Q000097:blood*; D008297:Male; D010314:Partial Thromboplastin Time / Q000379:methods*; D055815:Young Adult
chemical_list: D016682:Lupus Coagulation Inhibitor