PT  - JOURNAL ARTICLE
AU  - Monis, Grace
AU  - Ferrell, Chris
AU  - Reyes, Morayma
TI  - Lupus Anticoagulant Increases Activated Partial Thromboplastin time (PTT) Prolongation in Incubated 1:1 Mix
AID  - 10.29074/ascls.25.3.165
DP  - 2012 Jul 01
TA  - American Society for Clinical Laboratory Science
PG  - 165--169
VI  - 25
IP  - 3
4099  - http://hwmaint.clsjournal.ascls.org/content/25/3/165.short
4100  - http://hwmaint.clsjournal.ascls.org/content/25/3/165.full
SO  - Clin Lab Sci2012 Jul 01; 25
AB  - 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.ABBREVIATIONS: ANOVA - analysis of variance; BLUP - borderline LAC; FVIII - Factor VIII; IgA - immunoglobulin A; IgG - immunoglobulin G; IgM - immunoglobulin M; LAC - lupus anticoagulant; LIS - laboratory information system; MLUP - moderate LAC; NEG - negative; PTT - activated partial thromboplastin time; PT - prothrombin time; SLUP - strong LAC; SEM - standard error of the mean