Lupus anticoagulant increases activated partial thromboplastin time (PTT) prolongation in incubated 1:1 mix.

ABSTRACT

UNLABELLED 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) 11 mix assays with incubation. The prolongation in seconds of PTT 11 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 11 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 11 mixes in patients with LAC is influenced by both length of incubation time and strength of the LAC. CONCLUSIONS: When using PTT 11 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.