Anti-cardiolipin antibody testing and reporting practices among laboratories participating in a large external Quality Assurance Program

Aims: To investigate differences in anti-cardiolipin antibody (aCL) testing and reporting practices among diagnostic laboratories participating in the RCPA Quality Assurance Program (QAP) Immunology Program. Methods: A survey was sent to all 58 laboratories enrolled for aCL testing in the RCPA QAP Program requesting the following information: ( 1) manufacturer/type of assay; ( 2) isotype tested; ( 3) use of calibrators and controls; ( 4) whether calibrators, control and patient specimens were performed in singles or duplicates; ( 5) whether results were reported semi-quantitatively and/or numerically; ( 6) values used to define negative/positive and semi-quantitative cutoffs and how they were determined; and ( 7) whether interpretative comments were provided and their content. Results: Thirty-two surveys (55%) were received. Significant differences were present particularly in the following areas: ( 1) whether IgM isotype aCL testing was performed routinely or only on specific request; ( 2) whether controls/calibrators/ specimens were tested in singles or duplicates; ( 3) whether results were reported numerically and/or semi-quantitatively; ( 4) the values used to define negative/positive and semi-quantitative range cut-offs; and ( 5) whether interpretative comments were provided and their content. Conclusions: These differences in testing and reporting practices are likely to contribute to the variation in aCL results reported by different laboratories, particularly among those using the same assay.