Sex-specific cut-off for dilute Russell's viper venom time lupus anticoagulant test may be of value.

Background: Current guidelines recommend application of the 99th percentile to determine the cut-off value on at least 120 healthy donors regardless of sex for lupus anticoagulant (LA) ratio of each step. However, a statistically significant difference between the sexes has been found for LA ratio recently.

Objectives: To clarify whether this sex difference in dilute Russell's viper venom time (DRVVT) exists in various detection systems and the necessity of setting sex-specific cut-off values.

Methods: Blood samples from healthy donors were detected on 3 DRVVT detection systems, and the sex-specific cut-offs of DRVVT test were obtained based on the 99th or 97.5th centile of screen, confirm, and normalized ratios (NRs) grouped by sex in each system. One thousand one hundred twenty one female patients with suspected antiphospholipid syndrome (APS) were retrospectively investigated, the APS-associated clinical and laboratory characteristics of female patients stratified by different cut-offs of DRVVT ratio were compared.

Results: The DRVVT NRs of females were significantly lower than those of males on each system. The female patients with DRVVT NR between female-specific and regardless of sex cut-offs had higher positive rates of silica clotting time test and LA retest results after 12 weeks than those with DRVVT NRs lower than female-specific cut-off, there were also more patients who met the APS clinical criteria.

Conclusion: The sex difference of the cut-off value for DRVVT LA test is confirmed on multiple systems, the female-specific cut-off is lower than regardless of sex cut-off and may lead to more female patients being considered as high-risk population for APS.