PB0079 - Experience of Lupus anticoagulant laboratory diagnosis by applying the 2020 ISTH-SSC guidelines from a single tertiary care center in Kerala

Background: The guidelines fromInternational Society on Thrombosis and Hemostasis-Scientific and Standardization Committee (ISTH-SSC) advocate the use of internally established threshold values, pooled normal plasma (PNP) for ratio standardization and ratio for interpretation of mixing tests in lupus anticoagulant (LA) testing.Guidelines strongly emphasize the role of mixing step in diagnostic process.

Aims: To explore and contrast results,interpretations of LA testing when adhering to the ISTH-SSC guidelines versus alternative approaches.

Methods: The study was conducted at Haematology laboratory, approved by Ethical Committee (ECASM-AIMS-2023-242) at Amrita Hospital Kerala.Samples from 150 consecutive patients underwent LA testing in TcoagDT100 and Stagocompact max on two step(screening, and confirmatory tests)versus three-step(screening, mixing, and confirmatory tests) procedure respectively.Study also focus on differences in interpretation when employing internally determined cutoffs versus those provided by the manufacturer, a normalized ratio calculated using PNP for each run versus mean of reference interval, a normalized ratio versus index of circulating anticoagulant for interpreting mixing step, Use of commercial pool norm vs inhouse Pooled normal plasma(prepared from 20 healthy donors),use of prothrombin time and thrombin time along with APTT testing.

Results: The outcomes of LA testing were comparable when utilizing either in-house or manufacturer's cutoff values. Using normalized ratio based on PNP resulted in more positive dilute Russell's viper venom (DRVV) time outcomes compared to using mean of reference interval. Overall, there was good agreement in mixing test results when employing normalized ratio and index of circulating anticoagulant. Among 33 samples positive for DRVV Screen test, 12 and 21 were classified as LA-positive with three-step and two-step procedures respectively. Use of prothrombin time and thrombin time along with Activated partial thromboplastin time reduced false positive lupus result.

Conclusion(s): The choice of cutoff values and method of ratio normalization had limited impact. Conversely, comprehensive understanding of characteristics of mixing test is crucial to optimize its diagnostic potential.