In order to help laboratories with best practices in testing for LA, several organizations have set up guidelines. These societies providing guidelines include:
- International Society for Thrombosis and Hemostasis (ISTH)
- British Committee on Standardization of Hematology (BCSH)
- Clinical and Laboratory Standards Institute (CLSI)
While their guidelines did not harmonize, there were clear practices they all agreed on:
- All samples should have double centrifugation.
- Assays should include aPTT and dRVVT.
- Calculations should include the % correction of screen/confirmatory or LA ratio (screen/confirmatory).
- The mixing study should be performed on a 1:1 mix with pooled normal plasma (PNP).
- All lupus testing should include interpretation.
The differences between the society's recommendations, although minor, included:
- Testing order: screen-mix-confirm versus screen-confirm-mix
- When performing the ratio: PNP versus the mean of the reference interval
- Interpretations of the mixing study: Using cutoff versus no recommendation
- Reference interval cutoffs from 97.5 percentile to 99 percentile - if Gaussian
- Testing patients on vitamin K antagonist (VKA): using 1:1 mix with PNP versus undiluted plasma if the INR < 1.5
- Testing patients on unfractionated heparin (UFH): everything from no recommendation to interpreting with caution, as well as determining if heparin neutralization is effective
Although these guidelines do not align, they give laboratories a testing pathway to follow and hopefully provide a resource that can allow them to internally standardize their practices and adhere to that protocol.
