NO EVIDENCE OF THE HOOK EFFECT IN PERITONEAL-FLUID CA-125 MEASUREMENTUSING IMMUNOENZYMATIC 2ND-GENERATION ASSAYS - COMPARISON WITH IMMUNORADIOMETRIC ASSAYS

Objective: To monitor the occurrence of the hook effect in measurement s of peritoneal fluid CA 125 levels using two different immunoenzymati c second generation assays (ETI-II and EIA-II), and to compare these r esults with those obtained using the respective immunoradiometric vers ions of the assays (IRMA-II and ELSA-II). Study design: CA 125 levels were determined in peritoneal fluid and serum samples obtained from 45 women with gynecological diseases. The assays were carried out using IRMA-II and ETI-II (Sorin Biomedica) and ELSA-II and EIA-II (CIS Bio I nternational) assays. Occurrence of the hook effect and linearity of t he assays were evaluated. Statistical analyses were performed by Wilco xon's test and linear regression analysis. Results. Undiluted peritone al fluids, assayed for their CA 125 content, showed falsely underestim ated values of the antigen when IRMA-II and ELSA-II assays were perfor med. The phenomenon disappeared only at high dilutions of the sample ( > 50). Conversely, immunoenzymatic ETI-II and EIA-II assays performed on undiluted peritoneal fluids did not show underestimated CA 125 valu es. CA 125 values obtained by immunoenzymatic assay were lower than th ose obtained using their respective immunoradiometric versions at a di lution of 1:100 (P < 0.001). A good correlation was observed between E LSA-II and EIA-II (r = 0.929) CA 125 values. Conclusion: The EIA-II im munoenzymatic assay appears to be more suitable for CA 125 measurement in peritoneal fluid in that it is not subject to the hook effect and its results correlated well with those obtained via its immunoradiomet ric version.