Time-resolved immunofluorometric assay of human growth hormone

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