Data from about 1,000 laboratories participating in the Diagnostic Immunology portion of the 1978 Center for Disease Control Proficiency Testing Program provided infornation dealing with laboratory performance and trends in testing protocols. Ninety specimens were distributed in scheduled quarterly and semiannual shipments, and five additional specirnens were provided in a special survey. The specimens offered both qualitative and quantitative challenges for a wide variety of analytes which included syphilis serology, rheumatoid factor, bacterial agglutinins, hepatitis B surface antigen, immunoglobulins and other serum proteins, infectious mononucleosis, rubella, toxoplasma, antinuclear antibodies, and streptococcal exoenzymes. This paper summarizes the results of the 1978 program.
The data accumulated from 1969 to 1979 in the Diagnostic Immunology portion of the Center for Disease Control Proficiency Testing Program were evaluated for evidence of change in performance among the participating laboratories. Evidence of improved performance was found for the rubella, rheumatoid factor, tularemia, quantitative immunoglobulin (immunoglobulin G, A, and M), and hepatitis B tests. No evidence of change was detected for the streptococcal enzyme, C-reactive protein, infectious mononucleosis, antinuclear antibodies, Salmonella and Brucella agglutinins, and syphilis tests. Data obtained from other tests were inadequate to determine trends. In most tests, deficiencies were identified which could be corrected and thereby could improve performance. It is pointed out that proficiency testing not only improves laboratory performance, but also can be used to evaluate performance levels, identify method, standard, or performance deficiencies, educate, estimate impact of possible changes, serve as external quality control, and document changes.
A proficiency testing survey for carcinoembryonic antigen (CEA) was conducted by the Center for Disease Control. The results from 125 laboratories throughout the United States indicate that many laboratories perform satisfactorily, but some laboratories need substantial improvement. Failure to follow manufacturer's recommendations and failure to heed the indications of "out of control" control results were two of the reasons for poor performance. Results reported for samples with CEA levels of larger than or equal to 20 ng/ml showed that the direct method produced significantly higher values than the indirect method on either whole of diluted plasma. Almost one-fourth of the results reported in this survey were placed in the wrong nominal group. It was determined that the results were log normally distributed and, consequently, that statistical methods that are appropriate for this distribtuion should be used for the analysis of CEA results. Most of the variation observed was the result of poor comparability between laboratories rather than lack of precision within the laboratory. This indicates that better performance could be achieved by better standardization and closer adherence to established procedures.
Standaridizing test results for rheumatoid factor by comparing results obtained for an unknown with results obtained for a serum reference preparation decreased variance between laboratories, as measured in the Center for Disease Control proficiency testing program, by 77%. The amount of improvement was also estimated by the type of test and by the manufacturer's product. Standardization resulted in an increase in the number of reported results that were within a twofold dilution of the median value. The percentage increased from 50.3 to 93.7% for the slide tests and from 78.1 to 91.2% fro the tube tests. Decrease in variance by manufacturer's product ranged from 94 to 27%. The study demonstrated that adopting a reference serum standard could substantially improve the comparability of rheumatoid factor test results and that proficiency testing programs can be used to estimate improvement which could be expected as a result of standardization.
The changes in the types and numbers of tests used by participants in the Center for Disease Control Proficiency Testing Program for the detection of hepatitis B surface antigen from the beginning of the program in 1971 until October 1975 are analyzed; the implications of these changes are discussed. Changes in the use of agar gel diffusion, rheophoresis, counterelectrophoresis, complement fixation, reverse passive latex agglutination, radioimmunoassay, and reverse passive hemagglutination tests are reviewed. The performance of the participants for 1975 is reported, and factors related to performance (type or combinations of tests used, procedures used to confirm specificity, etc.) are discussed. The increase in the use of third-generation tests in place of tests with lower sensitivity and the decrease in the use of multiple tests undoubtedly represent increased efficiency and effectiveness.
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