Luminescence immunoassays applied to routine measurements of plasma proteins

Abstract

The aim of this presentation is to demonstrate that luminescence immunoassays for serum proteins can be introduced as routine laboratory methods. The small sample volume maximally 20 ~tl for ferritin makes the assays ideal for paediatric use. The serum proteins chosen were: ferritin, transferrin and caeruloplasmin as metalloproteins, orosomucoid, c-reactive protein and transthyretin as acute-phase proteins and ~l-foetoprotein as "tumour marker" and pregnancy risk parameter. The methods used were variations of solid-phase chemiluminescent immunoassays developed in this laboratory, namely SPALT (solid-phase antigen luminescence techniques) [1] and ILSA (immunoluminometric labelled second antibody assay), both of which used labelled second (species-specific) antibody, and ILMA (immunoluminometric assay) which used a labelled substance-specific (first) antibody, analogous to the immunoradiometric assay (IRMA). All assays had one reaction partner coupled covalently to a polystyrene ball (6.4ram diameter) as solid phase. The luminescent label adapted for all assays was N-(4-aminobutyl)-N-ethyl isoluminol hemisuccinamide (ABEI-H) which was commercially available (LKB, Mfinchen). This was converted into an N-hydroxysuccinimide ester, which was then coupled to the antibody in an analogous way to the BoltonHunter iodination of proteins. All assays were measured in either an LKB-1251 25 sample luminometer (LKB, Mfinchen) or an LB-950 300 sample luminometer (Labor Prof. Dr. Berthold, Wildbad), the latter being more suitable for assay runs with more than about 30 samples. Table1 shows the assay conditions, reference ranges in serum and relevant quality-control parameters for each assay. This article has demonstrated that luminescence immunoassays are fully capable of being used routinely, and need no longer be seen as "exotica" of little or no practical value!