1997 Revised Guidelines for Performing CD4+ T-Cell Determinations in Persons Infected with Human Immunodeficiency Virus (HIV)

On the basis of the reported number of tests performed annually by laboratories participating in CDC's Model Performance Evaluation Program for T-lymphocyte immunophenotyping in 1995, more than 1.6 million CD4+ T-cell measurements are performed yearly by the approximately 600 testing laboratories in the United States (77). Most of these measurements are made by using multi-platform flow cytometric methods, although new single-platform methods (both flow cytometric and others) are available (78-85). Recommendations concerning CD4+ T-lymphocyte immuno-phenotyping have focused on the more complex multi-platform process of measuring CD4+ T-cells. The recommendations for testing have increasingly been adopted (86), and as a result, laboratorians have reported improved testing practices (86, 87). Testing outcomes associated with following the recommendations include a) increased confidence in results, b) more reproducible results, c) increased ability to resolve discrepant problems, d) decreased proportion of unacceptable specimens received for testing, e) decreased proportion of specimens requiring reanalysis, and f) decreased incidents that could pose biohazard risks (86).

Although data suggest that guidelines for CD4+ T-cell lymphocyte immunophenotyping have improved many laboratory practices, developing guidelines that address every aspect of CD4+ T-cell testing (including some laboratory-specific practices) is not possible. Moreover, measuring the outcomes associated with the adoption of these guidelines is inherently difficult. First, the guidelines lack evaluation protocols that can adequately account for the interactions among recommendations. No weight of importance has been assigned for the individual recommendations that address unique steps in the testing process; hence, the consequences of incompletely following the entire set of recommendations are uncertain. Second, because published data were not available as the basis for every guideline, some recommendations are based on experience and expert opinion. Recommendations made on this basis, in the absence of data, may be biased and inaccurate. Finally, variations in testing practices and interactions among the practices (e.g., how specimens are obtained and processed, laboratory personnel credentials and experience, testing methods used, test-result reporting practices, and compliance with other voluntary standards and laboratory regulations) complicate both development of guidelines that will fit every laboratory's unique circumstances and measurement of the value of guideline implementation.

When the first CDC recommendations for laboratory performance of CD4+ T-cell testing were developed, the guidelines were written so as not to impede development of new technology or investigations into better ways to assess the status of the immune system in HIV-infected persons. Presentations at the second national conference in Atlanta indicated that although CD4+ T-cell testing by multi-platform flow cytometry is still being performed by most laboratories, other single-platform methods are being implemented. In addition, alternative T-cell phenotypic markers are being investigated as prognostic indicators or markers of treatment efficacy, alone and in combination with other markers (88).

Participants at the second national conference emphasized the need for monitoring the intralaboratory and interlaboratory accuracy, precision, and reliability of current and new procedures. Decisions about implementing and modifying procedures should be based on performance data collected to assess the extent to which the quality goals established by providers and users of laboratory testing services are achieved (76). In testing areas where no absolute gold standards exist (e.g., CD4+ T-cell enumeration), method validation and verification processes are even more critical. Laboratorians should continue to rely on as many sources of information and data as possible to help in their decision processes. Factors that have contributed to improved testing practices and that are important resources for laboratorians include regulatory and voluntary laboratory standards (29, 31, 32, 34, 89); manufacturer's recommendations; proficiency testing and performance evaluation program data; information shared at scientific conferences, meetings, and training sessions; and publications in scientific literature.

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