Consensus guidelines on anti-beta 2 glycoprotein I testing and reporting

Summary

Consensus guidelines on anti-beta 2 glycoprotein I (anti-β2GPI) testing have been developed to help minimise laboratory variation in the performance and reporting of assays for these antibodies. These guidelines include minimum and optional recommendations for the following aspects of anti-β2GPI testing and reporting: (1) isotype of anti-β2GPI tested; (2) specimen type; (3) controls and assay precision; (4) calibrators; (5) patient samples; (6) rheumatoid factors and IgM anti-β2GPI testing; (7) reporting of results; (8) cutoff values; and (9) interpretative comments. Issues related to inter-kit/assay standardisation and the manufacturing process of commercial anti-β2GPI kits/assays have not been addressed in the current guidelines.

Key words:

• Beta 2 glycoprotein I
• β2GPI
• antibody
• consensus
• guidelines
• testing

Notes

^AThe ‘I’ in beta 2 glycoprotein ‘I’ is the Roman numeral for ‘1’. As such, beta 2 glycoprotein ‘I’ is sometimes referred to as beta 2 glycoprotein ‘1’ (β2GP1).

^BFor example, the Reaads Corgenix anti-β2GPI kit insert indicates that citrated plasma can be used if the plasma specimen has been prepared by filtration (0.22 micron filter) or double centrifugation, to avoid platelet contamination (i.e., following guidelines for the collection of plasma for lupus anticoagulant testing). It also contains the warning that lysed or aged platelets can lead to aberrant results.

^CA recent report from Lewis et al. has reported essentially equivalent IgG β2GPI and IgM β2GPI results with the use of paired serum and EDTA plasma specimens using in-house ELISA-based methods and Bland-Altman Analysis.46-48 However, correction for the effects of dilution was required for citrated plasma specimens, to produce IgG β2GPI and IgM β2GPI results comparable with those obtained from paired serum specimens (the correction factor used was not stated by the authors).48 However, at present there are no published reports of similar evaluations with commercial β2GPI assays/kits.

^DThe maximum value of 20% is based on the inter-run variation data from aCL,21 anti-neutrophil cytoplasmic antibody (ANCA; Trevisin M, personal communication) and coeliac disease-related antibody (Reeves GE, personal communication) ELISA-based evaluations, and a confidential survey of inter-run variation data from laboratories currently using IgG anti-β2GPI assays.

^EThe potential for rheumatoid factors to produce falsely positive IgM aCL results has been previously reported,49 and was also found in an evaluation using two commercial methods (RELISA/Immuno Concepts and Medical Innovations aCL kits. Wilson RJ, Hendle MJ, Wong RCW, unpublished data). However, formal evaluation of the effect of rheumatoid factors and IgM anti-β2GPI results has not been reported.

^FUse of an IgG absorbant should be assessed on the IgM anti-β2GPI assay/kit used by the laboratory as it may vary between different assays/kits. No formal assessment of the effect of using an IgG absorbant on different IgM anti-β2GPI assays/kits has been reported. However, it was found that the effect of an IgG absorbant on IgM aCL values varied between different IgM aCL assays/kits (Wilson RJ, Hendle MJ, Wong RCW, unpublished data).

^GThe recent National Pathology Accreditation Advisory Council (NPAAC) Requirements For The Estimation Of Measurement Uncertainty (2007 Edition) document, contains a guideline (G7) that states ‘Laboratories should ensure relevant MU information is available’. The accompanying commentary includes the following comments: C 7.2 which states ‘It is important for laboratories to understand the clinical implications of the results of the measurements they report and to be aware of those where MU could affect clinical interpretations and patient management’; and C7.3 which states ‘Laboratories should consider providing relevant MU information with patient reports where it may be of clinical utility’.

^HA positive lupus anticoagulant (LAC) result appears to be a stronger risk factor for thrombosis than either a positive aCL or anti-β2GPI result.8,50 Furthermore, the combination of positive IgG anti-β2GPI and LAC results appears to be associated with an increased risk of thrombosis.9-12

^IFor example, in the case of laboratories that perform anti-β2GPI testing for other laboratories, where the IgG aCL test results from the referring laboratory are not available.

^JWhere IgG aCL testing does not appear to have been performed, it should be recommended in view of the higher sensitivity of IgG aCL compared with IgG anti-β2GPI for APS.4-7