Development of time-resolved immunofluorometric assays for CA 72-4 and application in sera of patients with gastric tumors

BackgroundImmunoradioassay (IRMA) with 125I-labeled monoclonal antibodies is widely used to measure levels of cancer antigen (CA) 72-4. We investigated a time-resolved immunofluorometric assay (TR-IFMA) to determine its sensitivity and specificity compared with those of IRMA.MethodsWe used 2 CA 72-4-specific monoclonal antibodies with different specificities. One was immobilized on a solid phase, and one was labeled with Eu3+. Serum from 44 adults with newly diagnosed gastric cancer and 208 control subjects was assayed by TR-IFMA and a conventional IRMA.ResultsThe detection limit of TR-IFMA was 0.55 U/ml. The calibration curve was linear to 1000 U/ml, with no hook effect up to 1000 U/ml. Intraassay CVs were 4.2–10.26% over the calibration range. Compared with IRMA, TR-IFMA had a broader analytical range and a shorter analysis time. At a cutoff of 99% specificity, TR-IFMA and IRMA results were positive in 37 and 26 patients, respectively.ConclusionsTR-IFMA is a rapid and sensitive nonradioactive method applicable to large-scale screening for CA 72-4. In addition to its broad, linear analytical range, TR-IFMA was more sensitive and specific than conventional IRMA. It was easy to perform and automate.