Among other issues relevant to antibody testing, the use of monoclonal or polyclonal antibodies for assay calibration has been a source of controversy. A wet workshop organized at APLA 2010 compared the performance characteristics of currently available monoclonal antibodies: HCAL (IgG) and EY2C9 (IgM). This study identified large variability in results obtained with the use of these monoclonal antibodies, currently distributed by the Centers for Disease Control and Prevention.11 Also, there are no guidelines available concerning the preparation and cross-validation of secondary calibrators or the evaluation of available preparations. On careful review of the data, the task force recommended that levels of secondary calibrators should be carefully defined following accepted procedures prior to use. The task force also decided that any aCL tests using monoclonal preparation as a calibrator should report aCL titers in GPL/MPL units, a method currently used by the majority of laboratories worldwide.
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Explore This IssueJanuary 2012
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The task force recommended an organized effort to evaluate further the performance of monoclonal and polyclonal antibodies and to identify optimal candidates for standardization. Once the candidate source is identified, the standard should be established according to current World Health Organization (WHO) guidelines to ensure its acceptance by regulatory authorities. Efforts focused on the development of international reference standards for IgG and IgM aCL and anti-β2GPI antibodies should be increased. In addition, a top priority of the task force will be to encourage all manufacturers to use the same calibrant material, whether human-derived polyclonal or monoclonal, so that this material can be designated as a WHO standard. This process could be facilitated by an internationally recognized organization. For the anti-β2GPI assay, there is no universal unit currently available. Therefore, the task force recommended the establishment of international units for measurement of anti-β2GPI antibodies. A work group has been assembled to carry out that objective, and a significant amount of work has already been completed.
Updated ISTH SCC guidelines on the use of LAC as a diagnosis of aPL antibodies incorporate a number of important issues. These issues include the following: definition of a “weak” LAC, as it is thought to be a confounding factor for diagnosis; false-positive screening assays secondary to the use of phospholipid-dilute reagents; embracing thrombin clotting time (TCT) and prothrombin time (PT) for the detection of LAC to determine the presence of heparin or warfarin interfering with test results; integrated testing systems; interpretative comments, as some factor inhibitors cause false-positive test results; and contacting reference laboratories for tests results and specific questions.12,13 Based on these considerations, the task force made recommendations described in Table 2 that were recently published.9