PubMed · 7005271
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A G Maciver, B L Mepham. 1980. Immunoperoxidase techniques and controls.. https://doi.org/10.1136/jcp.33.12.1218
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Technology with solid-phase enzyme immunoassay was markedly progressed. Kinds of solid-phase are as follows; (1) tube, (2) beads, (3) latex particle, (4) microtiter plate, (5) ferrite particle, (6) membrane. Recently, application of avidin/biotin system to the tube method was accomplished. As one of the B/F separation with beads method, spin washing method was also developed. Automated open system with the beads method was also developed. Microtiter plate using sponges as the solid-phase was routinely used for allergy tests (CAP-RAST). Multi-Access Open System (MAOS), applicable for various kinds of ELISA kit, will appear in Japan near future. Latex particle with ferrite plating and ferrite particle with glass coating were also used as the solid-phase of EIA. HCV-RIBA II and III systems using nitro-cellulose membrane as solid-phase were also described.
Although the basic concept for quality control of enzyme immunoassay (EIA) is the same as that of quality control of the usual chemical analysis, immunological analytic methods including enzyme immunoassay have some specific features depending on the method as compared with the chemical method. In addition to the usual QC method, therefore, it is necessary to add some QC techniques to control the variables derived from the method. In accuracy control of EIA, standard materials, reagents and analytical equipment will be the major sources of error. Points to be considered in accuracy control are described. In precision control of EIA, between-run precision is generally larger than within-run precision. In consideration of the characteristics, mean-Rs-R control chart method and Z-V control chart method appropriate for immunological method are described. Analytical sensitivity expressed as detectability and detection limits is very important in EIA. A procedure to determine the detection limits is described in detail. Between reagent lot difference in immunological reagent is considerably larger than that of chemistry reagent and a shift of the point on the control chart is not adequate to assess the reliability of the patient data. Therefore, an evaluation method of the between reagent lot difference is described. General procedures of precision control are not described here because the procedures are well known.
CEDIA assays represent a state of the art technique utilizing two genetically engineered, enzymatically inactive fragments of beta-galactosidase as the basis for a homogeneous enzyme immunoassay. The smaller, amino-terminal polypeptide, designated the enzyme donor (ED), can recombine spontaneously with the large residual fragment, called the enzyme acceptor (EA), to form active beta-galactosidase, in a process called complementation. ED have been designed in such a way that a ligand, such as a hormone or drug, can be chemically attached to a specific amino acid residue without affecting the enzyme complementation. However, the binding of a ligand-specific antibody to the ED-ligand conjugate will inhibit complementation. If a sample containing ligand is added to the reaction mixture, the ligand will compete with the ED-ligand conjugate for the limited number of antibody binding sites. Thus, the ligand concentration in the sample will modulate enzymatic activity by influencing the amount of free ED-ligand conjugate available for complementation. The basic technology of CEDIA assays has a number of inherent advantages, the most important of these being a linear calibration curve with high precision over the whole assay range, lack of endogeneous enzyme activity and minimal serum interference, chemically defined conjugates and flexibility in assay design. These provide significant advantages in comparison to other homogeneous immunoassay techniques. As a result, CEDIA assays have been successfully developed for high concentration drugs such as theophylline, phenobarbital and phenytoin as well as for very low concentration analytes such as digoxin, B12 and folate. In a modified assay format, even the determination of binding proteins has been accomplished, an example being thyroxine binding proteins in the CEDIA T-uptake assay. More recently, the methodology has been extended to the measurement of high molecular weight analytes like ferritin.