PB0112 - Antiphospholipid Syndrome: Determination of Cut-off Value for Lupus Anticoagulant test in Malaysian Healthy Blood Donors.

Background: Lupus anticoagulant (LA) test is a complex investigation with many compounding factors to be considered. It is also in need of standardization in a few important aspects, including cut-off values. Hence the recommendation for in-house cut-off value establishment.

Aims: This study was conducted to determine the cut-off value for LA test in Malaysian population.

Methods: 795 samples from healthy blood donors at a single collection centre were collected and analysed in specialised haemostasis unit of a tertiary referral centre, using LA-sensitive-activated partial thromboplastin time test (aPTT-LA) and diluted Russell Viper Venom Time (dRVVT) methods, utilizing STA Compact Max2 Analyser. Outliers were removed using Y algorithm and revised data were then analysed with cut-off value taken at 99th centile.

Results: 780 healthy donors were included in the cut-off determination, with male and female total number of 71% (n=556) and 29% (n=224) respectively. For both genders, majority of donors age from 31 to 40 years old. DRVV screen ratio and DRVV normalized ratio cut-off achieved in this study are ≤1.26 and ≤1.27 respectively, which are higher than the manufacturer’s cut-off value. Conversely, DRVV mixing normalized ratio cut-off attained is ≤1.16 which is comparable to that of manufacturer’s cut-off of ≤1.2, upon rounding up to 1 decimal point. Apart from DRVV confirm and DRVV mix normalized ratio, cut-off values among male donors are notably higher that their female counterpart.

Conclusion(s): The study further supports the need for in house cut-off value establishment as per recommendation by International Society on Thrombosis and Haemostasis (ISTH). Noteworthy is the difference in the cut-off value between gender, with higher results observed in the male population, albeit marginally in certain parameters. Further validation of the study cut off values is required prior to their use in the Malaysian population.