Lupus anticoagulant assay cut‐offs vary between reagents even when derived from a common set of normal donor plasmas

Abstract

Background: Multicenter studies reveal that diagnostic efficacy of lupus anticoagulant (LA) assays is enhanced if cut-offs are locally generated. However, a potential confounder is the inevitable use of separate normal donor populations.Objectives: Generate cut-offs for multiple LA reagents with the same analyzer and normal donor plasmas. Methods:Cut-offs for screen ratio, confirm ratio, percent correction of screen ratio by confirm ratio, and normalized screen/confirm ratio (NSCR) were derived from the same 50 normal donor plasmas for screen and confirm pairs for two dilute Russell's viper venom time reagents, LA1/LA2 and HEMOCLOT™ LA-S/LA-C, and two APTTs, Actin FSL/FS and Cephen LS/Cephen. The cut-offs were challenged with plasmas from 20 triple-positive APS patients and 25 plasmas from LA-negative, thrombotic patients. Results:Cut-offs for screen ratio, confirm ratio, percent correction, and NSCR, respectively, were 1.12/1.08/8.3/1.09 for LA1/LA2; 1.17/1.10/13.6/1.13 for HEMOCLOT™ LA-S/LA-C; 1.12/1.13/9.7/1.10 for Actin FSL/FS; 1.09/1.13/11.0/1.11 for Cephen LS/Cephen. LA1 and LA-S screens were elevated in 19/20 and 16/20 triple-positive plasmas, respectively, while 20/20 were detected with both via integrated interpretation ie, percent correction or NSCR irrespective of screen elevation.Actin FSL and Cephen LS screens were elevated in 17/20 and 19/20 triple-positive plasmas, respectively, while one more LA was detected with Actin FSL via integrated interpretation, but not for Cephen LS. Integrated interpretation suggested 5/25 LAnegative plasmas contained weak LA (two with Actin FSL/FS, two with LA1/LA2, one with LA-S/LA-R). Conclusions:Employing the same normal donor plasmas and analytical platform does not compensate for between-reagent differences when generating LA assay cut-offs. K E Y W O R D S activated partial thromboplastin time, antiphospholipid syndrome, dilute Russell's viper venom time, lupus anticoagulant, phospholipid dependence

International multicenter, multiplatform study to validate Taipan snake venom time as a lupus anticoagulant screening test with ecarin time as the confirmatory test: Communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

“…Although ISTH LA detection guidelines recommend 99th percentile cutoffs, it is problematic for many laboratories to source sufficient normal donors for an accurate 99th percentile estimation (>100). Furthermore, other guidelines and studies indicate that, in common with routine coagulation screening assays, LA assay population distributions are commonly Gaussian, or can be made so by data transformation, and that parametric evaluation can be applied on lower donor numbers 5,6,14,33,34,40,41 . All but one of the RRs were Gaussian or successfully transformed, so cutoffs were taken as mean +2 SD, equating to 97.5th percentile for normally distributed data 5,6,34 …”

Guidance from the Scientific and Standardization Committee for lupus anticoagulant/antiphospholipid antibodies of the International Society on Thrombosis and Haemostasis

“…Probably, they might be explained by the variation in reagent lots, as confirmed in another multicenter study with the same reagent lot used by all participating centers 77 . A more recent study showed poor interlaboratory agreement of cutoff value even when a common set of normal donors were investigated by different platforms 78 . These observations illustrate that because of many variables (eg, sample collection system, sample tubes, demographics of the normal population, variation in PNP, lot of reagents), cutoff values determined elsewhere cannot be transferred irrefutably from one laboratory to another.…”

“…77 A more recent study showed poor interlaboratory agreement of cutoff value even when a common set of normal donors were investigated by different platforms. 78 These observations illustrate that because of many variables (eg, sample collection system, sample tubes, demographics of the normal population, variation in PNP, lot of reagents), cutoff values determined elsewhere cannot be transferred irrefutably from one laboratory to another. In the meantime, it is still advised to determine in-house cutoff values 73 but joint efforts to calculate universal cutoff values per test/instrument combination should continue, to find a solution for this challenging issue.…”

Determination of cut-off threshold of normalized ratio for determining lupus anticoagulant in normal plasma of donors – healthy volunteers (large network laboratory study results)

“…Полученные результаты приближены к рекомендуемым пороговым значениям (менее 1,2) [3] и соответствуют недавнему исследованию [8] на той же аналитической паре (реагент и анализатор).…”