Presentation Details
| Preliminary findings of utilizing aPTT assay as a screening tool for lupus anticoagulant Suhhyun Kim, Daniel Sabath. Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA |
Abstract
Background: Existing literature suggests utilizing phospholipid depleted activated partial thromboplastin time (aPTT) assay to screen for presence of lupus anticoagulant (LA). While this may be feasible where LA testing is conducted for diagnosis of anti-phospholipid syndrome (APS) and in work ups of thromboembolic events and recurrent miscarriages, oftentimes testing for LA is ordered following an elevated aPTT result along with a mixing study in clinical scenarios where LA is not suspected initially. Although this has the potential to result in unnecessary testing for LA, the screening utility of initial aPTT for LA has not been thoroughly investigated. Objectives: The purpose of this study was to investigate the sensitivity and specificity of the initial screening test utilizing phospholipid based aPTT test for the detection of LA. Methods: The LA test results as well as associated mixing studies and the initial aPTT (STA-PTT, Diagnostica Stago) were reviewed from a population of in-house University of Washington medical system patient population for dates ranging from 1/1/2020 to 1/1/2023. LA results were compared with the initial screening aPTT results. Results: A total of 124 LA tests were identified following mixing studies and an aPTT result. The patient population comprised 60 males and 54 females from ages 19-89. Our preliminary results show that the initial aPTT test has a sensitivity of 87.1% and specificity of 30.1% with a positive predictive value of 29.3% and a negative predictive value of 87.5% for the presence of a LA. The correlation between the initial PTT and LA was not significant (r = 0.146, p= 0.105). In addition, a subset of 54 tests with elevated aPTT with mixing studies were identified. Of these, 30 had associated incomplete correction on mixing studies with 16 positive LA and 14 negative LA results. Of note, a repeated aPTT was measured with mixing study and LA test. aPTT measured with LA testing was significantly higher that initial aPTT and straight aPTT from mixing study (p= 0.039 and 0.014, respectively). Conclusions: Our preliminary results show that aPTT as a screening assay is sensitive but has low specificity, indicating that it has a high probability of false positives. A subset of tests with elevated PTT with incomplete correction showed equivocal LA end results. In addition, for this subset of test, the repeat aPTT measurement with the LA testing was elevated. Further studies with larger sample size with these test parameters are underway to tease out the potential elevation in aPTT and investigate the efficacies of the utilities of aPTT assay as a screening tool in various clinical settings where LA is not initially clinically indicated.
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No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.