ABSTRACT
We review the following labels used as substitutes for radioisotopes in immunoassay systems: bacteriophages, chemiluminescence precursors, fluorochromes, fluorogens, fluorescence quenchers, enzymes, coenzymes, inhibitors, substrates, various particulates, metal atoms, and stable free radicals. New methods for performing immunoassays with these labels are described where appropriate. Methods that require no separation steps and offer special promise for easy automation are noted.
Subject(s)
Chemistry, Clinical , Immunoassay/methods , Bacteriophages , Erythrocytes , Fluorescent Dyes , Free Radicals , Humans , Luminescent Measurements , Radioimmunoassay/methods , Spectrometry, FluorescenceABSTRACT
We describe an immunoassay for thyroxine in serum. In the assay specific antibody covalently bonded to latex particles is used, along with horseradish peroxidase as the label, and o-phenylenediamine as the chromogen. The flexible protocol is designed for manual execution. Performance is similar to that of the highest-sensitivity thyroxine radioimmunoassays. Results correlate well with radioimmunoassay (r = 0.99, slope = 0.93, y-intercept = 2.4 microgram/liter for 201 samples) and an automated enzyme immunoassay (r = 0.97, slope = 0.99, y-intercept = 4.7 coefficients of variation are less than 7.2% over the entire useful range of the assay (20--240 microgram/liter). The limit of detection is less than 94 pg/tube at 20 microgram/liter. Only D-thyroxine is known to interfere with serum assays. This assay has no discernible protein effect from 40 to 80 g of protein per liter, unlike many thyroxine radioimmunoassays. Serum preservatives known to be peroxidase inhibitors do not adversely affect assay performance because of the 56-fold dilution in the final assay mixture. Hemolyzed serum and EDTA-treated plasmas are unsuitable for this assay.
Subject(s)
Thyroxine/blood , Cross Reactions , Humans , Immunoenzyme Techniques , PhenylenediaminesABSTRACT
This review discusses the various technical problems likely to be encountered in digoxin assay using 125I methods. Many of these difficulties are not limited to digoxin, but are potential dangers when measuring a wide variety of substances by radio-ligand techniques. Emphasis is placed on ways to avoid or solve these problems. Beside error induced through technical aspects, which include radio-ligand reagents, dispensing equipment, and well counters, other potential sources of interference which are considered are the effects of medications, serum proteins, and previously administered radioactivity.
Subject(s)
Digoxin/blood , Radioimmunoassay/methods , Antibody Specificity , Antigen-Antibody Complex , Blood Proteins/analysis , Digoxin/administration & dosage , Dose-Response Relationship, Drug , Humans , Iodine Radioisotopes , Protein Binding , Quality Control , Radioimmunoassay/instrumentation , Radioligand Assay/methodsABSTRACT
Pitfalls in Iodine-125 digoxin methods are reviewed. Problems may arise from instrumentation, reagents, methodology, medications and variation in patient specimens. The laboratory has an obligation to avoid these errors and ways are available to accomplish this.
