COMPARISON OF RUBELLA IMMUNOASSAYS GA, has recommended that a positive result by any test for rubella antibody be accepted as evidence of rubella immunity, z In support of this recommen- dation are several studies that have shown that low antibody titers, particularly those detected by latex agglutination, are sufficient to protect against in- fection with attenuated virus. 8’1z The latex aggluti- nation methods (Rubascan and Rubalex), as dem- onstrated in this study, are as sensitive, specific, and accurate as other methodologies. They also have the advantages of requiring no pretreatment of se- rum samples, small sample volume, rapid turn- around time (less than 10 min), and no purchase of capital equipment. The 3 remaining assays are either fully auto- mated (IMx) or semiautomated (FIAX and Ruba- zyme). Previous studies on the fully automated IMx rubella IgG assay have shown that the system is more sensitive than and as specific as conven- tional EIA technology. 16,18 Schaefer et al. 8 showed that the IMx had a sensitivity of 99.9% compared to a sensitivity of 96.5 % for Rubazyme. Specificity was identical for both assays at 98.9%. Similar results were obtained by Abbott et al. 16 and Skurrie et al. 19 In these previous studies, the IMx was only compared to conventional EIA with discordant re- sults referred by passive hemagglutination. Other commercially available systems such as latex agglu- tination and fluorescent immunoassay were not eval- uated. In the present study, the IMx was found to be more sensitive and accurate than fluorescent im- munoassay but equivalent to the latex agglutination assays and conventional EIA. The primary purpose of rubella screening is to identify non-immune women of childbearing age. Therefore, a false positive result would be an error with the most serious consequences since women who are truly non-immune would not be vaccinated and would be fully susceptible to rubella infection. Subsequent infection during pregnancy would pose a risk to the unborn fetus. On the other hand, a false negative result, although not as serious, could result in potential morbidity to the patient due to unnecessary vaccination. The FIAX method showed the lowest diagnostic accuracy (95%), primarily due to a 10% false negative rate. The other methods evaluated had diagnostic accuracies ranging from 96% to 99%, with few false positive or false nega- tive results. On the basis of the results presented here, all of the methods evaluated, with the possible SA UTTER ET AL. exception of the FIAX assay, can be used reliably to determine rubella immune status. ACKNOWLEDGMENTS This work was funded in part by Carter Wallace, Inc., Cranbury, NJ. REFERENCES 1. 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