Cooperation experience in a multicentre study to define the upper limits in a normal population for the diagnostic assessment of the functional lupus anticoagulant assays

Abstract

The study allowed us to define a uniform approach to LA testing and evaluation for laboratories employing the same methods.

Trials and tribulations in lupus anticoagulant testing

“…As noted at [10,11] . Unauthenticated Download Date | 5/11/18 11:37 AM the start of this commentary, the report from Pradella and colleagues [1] identified a statistically significant interlaboratory difference in some test times when these were expressed in seconds, but not when expressed as ratios. In this study, all laboratories used the same tests, the same reagents and the same type of instrument.…”

“…includes a report by Pradella and colleagues regarding a cooperative multicentre study to define the upper limits of normal for several tests used in the diagnostic assessment of lupus anticoagulant (LA) [1] . In total, 200 normal samples were assessed, comprising 40 from each of five centres, for a total of six functional LA assays.…”

“…This has caused some contention in the field, given that a statistically valid 99th percentile evaluation of a nonGaussian distributed normal population would require a minimum of nearly 400 samples [6] . Pradella and colleagues [1] comparatively evaluated the data obtained in each assay, as well as assay ratios, in each center, as well as the composite of all study data. Notably, when assay data was expressed in seconds, some test results showed a normal Gaussian distribution, whereas others did not, and there were also some statistically significant differences in results obtained between centers.…”

“…Of interest, Pradella and colleagues [1] determined a cut-off value of 1.22 for the dRVVT normalised ratio. This value is actually very close to that value ' nominally ' indicated on many dRVVT product information sheets, as well as generally used by laboratories.…”

Lupus anticoagulant

“…This approach provides a reliable method for setting the upper limits on healthy subjects for dRVVT and silica clotting time (SCT) integrated assays [12], thus identifying the negative population. It is important to define a method for determining the cutoff value aiming to reduce equivocal borderline results and improving interlaboratory comparability [13].…”