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Representatives of INOVA Diagnostics respond to the letter by Drs. Hoefner and Yeo:

INOVA Diagnostics Inc., San Diego, CA 92131-123

^aAuthor for correspondence.

To the Editor:

Anticardiolipin antibody (ACA) tests are among the most difficult of all ELISAs to standardize. There are the well-known difficulties of adhering the phospholipid to a plastic microwell plate. In addition, the antigen solid phase is complex, consisting of both the phospholipid plus a necessary cofactor, known as ß₂-glycoprotein (ß2-GPI), and the blocking agent. Then there is the added problem of having to calibrate each reagent set to a reference preparation that consists of pooled human sera. As mentioned by Drs. Hoefner and Yeo, there have been four different variations of these standards over the years, and despite the best efforts of the producers of these standards, some drift can occur at different parts of the assay range.

It is for these reasons that experts in the ACA field, including those responsible for producing the standards in question, recommend that results be reported in a semiquantitative manner. It has been further recommended that only moderate or high concentrations of IgG and IgM ACA be considered diagnostically important and that two positive results obtained 6 or more weeks apart are necessary.

Shown in Table 1 are data from the most recent College of American Pathologists survey for sample ACL-04 for the top four manufacturers’ reagent sets. Although the median values of three of the four methods are relatively close (43–48 units), the fourth is much different, and the CVs and ranges for each method are high. These data confirm that some variation in the ACA test is unavoidable and expected.

Drs. Hoefner and Yeo have asked that laboratories be informed when systemic changes occur. This is customary INOVA Diagnostics policy. In the case of the ACA IgM test, we and others did notice a shift in the reference preparation (Harris) that all manufacturers claim to use, but internal testing of our own patient panel did not reveal changes in the diagnostic result substantial enough, in light of the semiquantitative nature of the method, to warrant customer notification. Furthermore, a review of internal laboratory control values across several lots of reagents provided to us by Drs. Hoefner and Yeo during our attempts to resolve the situation again revealed no diagnostic changes in the semiquantitative results obtained with the reagent sets.

This Article Extract Full Text (PDF) Submit an electronic Letter to the Editor about this paper Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Binder, W. L. Articles by Myers, B. Search for Related Content PubMed PubMed Citation Articles by Binder, W. L. Articles by Myers, B.