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These guidelines were developed by CDC for laboratorians who perform immunophenotyping for detection and enumeration of CD4+ T-cells and other lymphocyte subsets in persons infected with human immunodeficiency virus (HIV). The guidelines describe single-platform technology (SPT), a process in which absolute counts of lymphocyte subsets are measured from a single tube by a single instrument. SPT incorporates internal calibrator beads of known quantity in the analysis of specimens by three- or four-color flow cytometry. With CD45 gating, the relative numbers of beads and lymphocyte subsets are enumerated, and their absolute numbers and percentage values are calculated. This report supplements previous recommendations published in 1997 (CDC. 1997 revised guidelines for performing CD4+ T-cell determinations in persons infected with human immunodeficiency virus [HIV]. MMWR 1997;46[No. RR-2]) that describe dual-platform technology, a method in which absolute counts are derived from measurements obtained from two instruments--a flow cytometer and hematology analyzer. The new recommendations address concerns specific to the implementation of SPT as well as other general topics such as laboratory safety and specimen handling.

Until 2001, the only test used to diagnose latent tuberculosis infection (LTBI) was the tuberculin skin test (TST). However, in 2001, a new test (QuantiFERON-TB or QFT; manufactured by Cellestis Limited, Carnegie, Victoria, Australia) that measures the release of interferon-gamma in whole blood in response to stimulation by purified protein derivative was approved by the Food and Drug Administration. This statement provides interim recommendations for using and interpreting QFT. As with TST, interpretation and indicated applications of QFT differ for persons according to their risk for LTBI and for developing tuberculosis (TB). This report provides guidance for public health officials, health-care providers, and laboratorians with responsibility for TB control activities in the United States in their efforts to incorporate QFT testing for detecting and treating LTBI. Regardless of the test used to identify LTBI, testing should be primarily targeted at diagnosing infected patients who will benefit from treatment.

Guidelines and Recommendations
Stephen B. Thacker CDC Library collection