The dilution effect of equal volume mixing studies compromises confirmation of inhibition by lupus anticoagulants even when mixture specific reference ranges are applied
Abstract
Introduction One of the recommended criteria for the laboratory diagnosis of lupus anticoagulants (LA) is demonstration of inhibitory activity. This is confirmed by performing mixing tests with normal plasma, usually in a 1:1 ratio, and demonstrating persistence of an abnormal clotting time in the screening test with significant confirmatory test reduction. However, the mixing with normal plasma can dilute the antibodies to undetectable levels and generate apparent negative results. No guidelines or consensus exist in how to interpret mixing study results.Patients and methods The present study assessed the 1:1 mixing study results from 600 patients with a thrombotic history positive for LA demonstrated in neat plasma by individual assays, or combinations, of dilute Russell's viper venom time, dilute activated partial thromboplastin time, activated seven lupus anticoagulant assay and Taipan snake venom time, plus confirmatory tests. Mixing tests were assessed initially using locally derived neat plasma reference ranges and subsequently with mixture specific ranges.Results The mixture specific ranges had lower upper limits. Of the total LA positive results, 32.5% were positive in the mixing studies when neat plasma reference ranges were applied, and a further 11.2% demonstrated LA activity when using the mixture specific ranges. The remaining 56.3% had been diluted such that they did not elevate the screening test above the upper limit of normal or generated minimal prolongation with an insignificant difference between the screen and confirmatory test result sufficient to confirm LA activity.Conclusions The significant impact of the dilution effect in 1:1 mixing studies emphasises the limitations of mixing studies as a vehicle for confirmation of inhibition by LA antibodies.
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The correction does not rule out the presence of inhibitors.
“The correction does not rule out the presence of inhibitors, considering the dilution effect [18]”
From Performance characteristics of 5 numerical indexes in mixing test interpretation under coexistence of lupus anticoagulant and coagulation factor deficiency (2023) · cites this paper as [18]
The mixing of weak LA samples may introduce loss of detectable LA activity and false-negativity give rise to inaccurate interpretation if the mixing test result is employed as a decision point for subsequent confirmatory test performance.
“The mixing of weak LA samples may introduce loss of detectable LA activity and the false‐negativity give rise to inaccurate interpretation if the mixing test result is employed as a decision point for subsequent confirmatory test performance.14, 31, 32, 33”
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- Authors
- Moore, G. W., & Savidge, G. F.
- Affiliations
- St Thomas' Hospital (GB)
- Corresponding author
- Moore, Gary W.
- ORCID
- Moore, Gary W.
- Venue
- Thrombosis Research
- Publisher
- Elsevier BV
- Published
- 2006-01
- Volume
- 118
- Issue
- 4
- Pages
- 523-528
- ISSN
- 0049-3848 (ISSN-L)
- OpenAlex
- W2026452950
- Cited by
- 46
- References
- 24
- Citations by year
- 2025: 2 · 2024: 4 · 2023: 7 · 2022: 5 · 2019: 3 · 2018: 1 · 2017: 4 · 2016: 3 · 2015: 1 · 2014: 2 · 2013: 4 · 2012: 5
- FWCI
- 0.61
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Thrombosis Research (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Rheumatology › Systemic Lupus Erythematosus Research
- Health Sciences › Medicine › Hematology › Blood Coagulation and Thrombosis Mechanisms
- Health Sciences › Medicine › Pulmonary and Respiratory Medicine › Vasculitis and related conditions
- Keywords
- lupus anticoagulant, mixing studies, dilution effect, antibody inhibition, confirmatory testing, dilute Russell's viper venom time, thrombosis, anticoagulant screening
- MeSH terms
- Blood Coagulation Tests, Humans, Partial Thromboplastin Time, Prothrombin Time, Reference Values, Sensitivity and Specificity, Reproducibility of Results, Lupus Coagulation Inhibitor
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