Abstract in the June Abstracts issue of Clinical Chemlstrytwo abstracts were mistakenly marked as withdrawn. The two abstracts that appear below were presented during the 1987 AACC National Meeting. 038 Clinical Evaluation of Quantitative Serum Bata-HCG Inoausays:Analysis of Discordant Beta-HCG Results, Norman J. kruse* Bonnie Johnson, and Ruth Lee** (Medlab, Portland, OR 97212) (Spon. N.J.kruse) Clinical evaluation of 4 commercial serum beta-HCG methods (Abbott, American Bioclinical, and Hybritech) were prformed using patient specimens predominantly for pregnancy determinations and related conditions. Discordant results were analysed at least twice in each method and additional serum specimens from the patient were obtainedand analysed in most cases of discordance. All methods were analysed for precision, sensitivity, cross-reactivity with homologous hormenes, and for effects of hemolysis and lipemia. Standardization and sensitivity differences between assays were determined. Reproducible, clinically significant discordant beta-HCG results were identified that were unrelated to standardization or sensitivity differences, LH cross-reactivity; or obvious serum matrix differences. These discordant results were stable, low-level (25-200 mIU/ml HCG)false positives with no evidence of pregnancy, trophoblastic disease or HCG-secreting malignancy (cf. R.0. Hussa, Obstet, S Gynecol, 65, 211, 1985). The rate of occurence of these patients was approximately 0.5% in our analysis of over 2000 patients with 2 competitive binding immunoassays using highly-specific polyclonal or monoclonal antibodies. Immunoassays using Immunoradiometric (IRMA) or ELISA "sandwich" assay technology showed lower false positive rates. One false-positive result in the ELISA assay (Abbott) was observed apparently due to rhematoid factor. No false-positive results were observed in the Hybritech IRMA using monoclonal antibodies. Stable low-levelfalse positive beta-HCG results can be a relatively rare, but significant problem in some beta-HCG methods. Our analysis of 2 methods using "sandwich" immunoassay technology (IRMA or ELISA) revealed that the occurence of these results can be greatly reduced or eliminated. *Present address: Triton Biosciences. Alameda, California **present address: Epitope, Beaverton, Oregon 97006 177 AFFINITYTM SYSTEM: TOTAL AUTOMATED DIAGNOSTIC TESTING WITH RANDOM ACCESS CAPABILITY, T.R. Witty, H.L. Larriva, M.E. Asti11 and G.H. Thorne, (becton Dickinson, Salt Lake City, Utah, 84116) (Spon: T.R. Witty) Becton Dickinson's AFFINITYTM system is a non-isotopic, automated. bench-top in vitro diagnostic instrument. The key element is the ready-to-use reagent package called an ImmUnitTM (patent 4608231) for immunoassays, identified by a unique barcode for each teat as well as a specific identifier for each unit. This ideatification is coupled with a scheduling algorithm which allows for any test with up to 3 incubations of varyine time to be run in any combination. A test is started by loading the tray with the desired test Unit(s) whereupon the instrument loads the Unit(s) onto the internal carousel for inventory and processing. The entire run is prioritized and scheduled including both STAT and routine samples. Up to 30 separate Units can be resident on the carousel. at any time with 16 more awaiting loading. Each time loading occurs, the run is updated and scheduled. By careful control of fluid handling and complete washing, each assay is independent of other assays. This eliminates load scheme restriction. The system can detect either fluorescence or color directly in the l2mm tube present in each test unit and internally correct for tube variation. This premise was tasted by running each of dieoxin, hTSH, TUptake and hCG in the presence and absence of 2 other tests then comparing the baseline with the random loaded run. The observed mean of 3 test pools when run in the presence of the other analytes was 99.7% +/- 4.1% of expected (N-12). The observed precision range on the baseline run was from 0.8-9.2% CV. mean=3.7% (N=12) while random was 1.5-9.1% CV, mean=4.5% (n=12). No significant differences were observed. The combination of the unitized package, barcode initiated scheduling algorithm and fluorescence/ooloriometrtc detection leads to a unique and flexible bench-top device compatible with a variety of diagnostic tests.