Highlights
- •The current ISTH-SSC guidelines for LA testing aim to harmonize practices.
- •However, methodologies are not always consistent and alternatives are possible.
- •The impact of the cut-off value used and the way to normalize ratios remained limited.
- •It is important to understand the mixing test characteristics.
Abstract
Background
The ISTH-SSC guidelines for lupus anticoagulant (LA) testing recommend using in-house
determined cut-off values, pooled normal plasma (PNP) for ratio normalization, and
a ratio for the mixing test interpretation. They strongly support the mixing step
role in the diagnostic process.
Objectives
To investigate and compare the LA testing results and interpretations obtained following
the ISTH-SSC guidelines or the available alternatives.
Patients/methods
Blood samples for LA testing from 462 consecutive patients were evaluated for screening,
mixing and confirmatory tests. The analysis focused on the interpretation differences
between using (1) the in-house cut-off values versus the manufacturer's cut-off values,
(2) a normalized ratio calculated using PNP at each run versus the mean of the reference
interval, (3) a normalized ratio versus the index of circulating anticoagulant to
interpret the mixing step, and (4) a two-step versus three-step procedure.
Results
LA testing outcomes were comparable when using the in-house and manufacturer's cut-off
values. More positive dilute Russell's viper venom (DRVV) time results were obtained
with the normalized ratio based on PNP than with the mean of the reference interval.
Overall, the mixing test results obtained with the normalized ratio and the index
of circulating anticoagulant showed a good agreement. Among the 97 DRVV Screen test-positive
samples, 33 and 89 were classified as LA-positive with the 3-step and the 2-step procedure,
respectively.
Conclusions
The cut-off value used and the way to normalize ratios had a limited impact. Conversely,
it is important to understand the mixing test characteristics to maximize its diagnostic
potential.
Graphical abstract
Graphical Abstract
Keywords
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Article info
Publication history
Published online: February 17, 2023
Accepted:
February 14,
2023
Received in revised form:
February 10,
2023
Received:
November 7,
2022
Identification
Copyright
© 2023 Elsevier Ltd. All rights reserved.
