TypIcal CEA, concn, ng/mL Intra-assay

Both the direct reading on the cup walls and the enhance-ment methodologies have their advantages. In the direct-reading system, a manipulative step is omitted and there is no waiting after the last wash before reading; this is as simple as nu but requires the derivatization of each specific chelating ligand used. The enhancement methodolo-gy uses common derivatized chelates such as DTPA, already available for other purposes, to carry the metal, therefore making this approach cheaper. Several good chelating li-gands are known for the enhancement step, but this re-quires a reagent addition and a 10-mm waiting step. In cases where the ligand available for direct reading does not provide sufficient sensitivity, the two methods may be used consecutively, as demonstrated in this paper, invoking the extra step of enhancement only to increase sensitivity. We are grateful to Baxter Healthcare Corporationforsupport and kind permission to publish thiswork. We also acknowledge Elsie W. Ewing and Lorraine M. Goodwin for technicalassistance and Lena Alberico who raised the ononoclonalantibodiesusedin this work. related staining techniques. Amsterdam: Elsevier/North-Holland Biomedical Press, 1978:67-80. 2. Soini E, Hemnula I. Fluoroimmunoassay: present status and key Inter- problems [Review]. Clin Chem 1979;25:353-.61. assay1 3. Soini E, Kojola H. Time-resolved fluorometer for lsnthanide 40 chelate&-a new generation of non-isotopic immunosasays. Cli