Revisiting the anticardiolipin test and its standardization

Although the importance of the anticardiolipin test in diagnosis of antiphospholipid syndrome (APS) is widely accepted, there remains much misunderstanding about the strengths and weaknesses of this assay. Several disorders result in formation of low levels of the antibody, hence the anticardiolipin test is not specific when results are low positive. In general, the higher the anticardiolipin level the greater the likelihood of a diagnosis of APS. Hence there have been numerous efforts to enable reproducible measurement of anticardiolipin levels. Standard calibrators were introduced to construct calibration curves from which levels of unknown samples can be derived. Those standard calibrators were made by mixing varying quantities of high positive with normal sera. More recently, calibrators derived from monoclonal anticardiolipin antibodies have been introduced. There are advantages and disadvantages with both types of calibrators. Determination of a precise and reproducible anticardiolipin level is difficult, whatever the calibrators used, because the assay is dependent on several variable components, any of which may fail on any given day. Utilization of a semi-quantitative measure (low, medium, high) may suffice in most clinical settings and would be less subject to error. Validated ELISA kits may offer greater reproducibility, since there is less variability than bench assays set up in very different laboratories. Whether using a kit or a bench assay, meticulous attention to detail offers the best opportunity for precision and reproducibility.