Assessment of Normative Range and Deriving Cut-Off Values for Lupus Anticoagulant Testing: An Experience from a Tertiary Care Center in Southern India
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Lupus anticoagulant (LA) testing is a demanding laboratory test. The most common among recommended tests for LA are dilute Russell viper venom time (dRVVT) and LA sensitive activated partial thromboplastin time (LA-aPTT). Although integrated test systems come with manufacturer assigned cut-off, but according to guidelines cut-off should be locally-derived. This study was carried out to find normative range of LA using LA-aPTT and dRV VT tests in south Indian population (n = 100) and using locally derived cut-off values to interpret patient samples (n = 152) in a one-year study period. Cut-off (mean+2.3 SD) for aPTT, LA-aPTT, dRVVT screen and dRVVT confirm assays were 37.5, 45.7, 45.5 and 41.3 s and for normalized ratio and percentage correction of ratio were 1.16 and 15.8% respectively. Among patients, 25 (16.4%) were positive of whom 14 were positive by normalized ratio, seven by LA-aPTT and four were positive by both. Four additional patients could be identified using local cut-off. While the specificity of all screening tests was high, sensitivity of only dRVVT screen was high. All testing laboratories should attempt to derive normative range and locally-derived cut-off. While dRVVT is a good screening test with high sensitivity, however combining LA-aPTT offers advantage of picking up cases negative by dRVVT.
KeywordsLupus anticoagulant Cut-off Locally-derived Normative range dRVVT LA-aPTT Normalized ratio
JIPMER intramural grant in support of MSc-MLT dissertation.
Compliance with Ethical Standards
Conflict of interest
The authors declare that they have no conflicts of interest.
Informed consent was taken from all the study participants and the study was approved by the Institute Ethics Committee.
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