TIME-RESOLVED IMMUNOFLUOROMETRIC ASSAY OF HUMAN GROWTH-HORMONE

We describe a time-resolved immunofluorometric assay (trIFMA) for huma n growth hormone (hGH), in which monoclonal antibody (mAb)-coated micr otiter strip wells and a europium (Eu) chelate-labeled mAb are used. W e compare the new trIFMA, in which two mAbs are used, with an immunora diometric assay (IRMA) in which polyclonal antibodies are used. Serum samples (n = 185) from 36 children with various diagnoses were analyze d. In addition, 24-h profile samples (72 per child) from 39 children w ere analyzed. The trIFMA was more sensitive (detection limit, 0.03 mIU /L) than existing IRMAs. Both the intra- and interassay CVs were less- than-or-equal-to 10.6% for hGH concentrations between 1 and 100 mIU/L. The trIFMA is technically simple and rapid, requires no centrifugatio n or separation reagent, and has a counting time of only 1 s per sampl e. In addition, the Eu label is nontoxic, presents no waste-disposal p roblems, and has a long shelf-life. Finally, the assay requires only s mall volumes of serum (25 muL), which is of considerable importance in pediatric use. The mAbs used for the trIFMA selectively bind the 22-k Da form of hGH, with the result that the assay detects about 80% of th e amount detected by the polyclonal IRMA.