Standardization of hapten immunoprocedures: total cortisol.

The broad objectives of this report are to enhance the clinical utility of the results of hapten measurement immunoprocedures by encouraging standardization of the procedures. It was decided to restrict the subject of the report to one analyte, and cortisol was chosen because of its diagnostic importance, the need for improved comparability with routine procedures, and its relevance to many other analytes. Therefore, the immediate objectives are to improve the clinical utility of total serum cortisol concentrations measured on different occasions and in different laboratories, to make diagnostic reference intervals more reliable and widely applicable, and to improve diagnostic accuracy by: Improving the agreement between results from reference measurement procedures and the results obtained with normal routine immunoprocedures for the measurement of total serum cortisol, and hence the comparability of routine results; and Reducing the susceptibility of the immunoprocedures to crossreactivity and interference. It is recognized that good comparability of results depends on procedures which are specific, properly calibrated and validated, and that the most important factors are resistance to crossreactants and interferants. Analytical goals for cortisol immunoprocedures are zero bias for 'all' samples with respect to a reference procedures, with the total analytical standard deviation equal to, or less than, half the within-individual standard deviation for cortisol, or 7.6% according to a recent estimate. To these ends the group proposes the following measures: 1. An international network of reference laboratories for cortisol measurement should be established, and progressively developed to include other hapten analytes. The service of the participating laboratories would be necessary to make feasible other recommendations listed below. 2. Procedures should be comprehensively validated, including a thorough crossreactivity study with the results presented to indicate the possible significance of each crossreactivity, a direct comparison of results with those obtained by a reference procedure for an adequate number of varied fresh/frozen patient samples, and suitable clinical validation studies. 3. External quality assessment schemes should assess participating laboratory performance against reference procedure values, and not consensus values related to values determined by any group of participating procedures. They should also assess the ability to determine added standard and to resist common interferants. 4. Master calibrators for use in the production of calibrators included in commercial kits, and formulated identically to these, should be certified with at least one reference measurement procedure, so that the concentrations of analyte in calibrators can be traced back to concentrations determined by a reference procedure.(ABSTRACT TRUNCATED AT 400 WORDS)