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- Grace Monis, MD-PhD
- Chris Ferrell, MT(ASCP)
- Morayma Reyes⇑
- Address for Correspondence: Morayma Reyes, MD-PhD, 815 Mercer Street Room 332, Box 358050, Seattle, WA 98195, 206-616-5004, morayma{at}u.washington.edu
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.
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
- © Copyright 2012 American Society for Clinical Laboratory Science Inc. All rights reserved.
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