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Human immunodeficiency virus (HIV) infection, regardless of clinical stage, produces many biologic indicators of virus infection, replication, or both (Fig. 5.1). Such indicators include viremia, antibodies against viral proteins, circulating viral proteins, and nonspecific markers of infection such as neopterin, 32-microglobulins, and changes in the absolute number of and the ratio of CD4 and CD8 cells. Most of the markers can be detected and in many cases semiquantified by serologic tests (Table 5.1). These tests have been used to protect the blood supply, diagnose infections, monitor the progression of disease, monitor the efficacy of drug therapy, and diagnose infections in infants born to HIV-infected mothers. The availability of highly specific, inexpensive tests for HIV antibody, such as the enzyme immunoassay (EIA), have permitted public health agencies to conduct-large scale seroprevalence surveys to define the epidemic.

Quality assurance is the dynamic and ongoing process of monitoring the diagnostic laboratory’s testing system for reproducibility that permits corrective action when established criteria are not met. Those techniques include statistical quality control procedures and procedures for method selection, method evaluation, preventive maintenance, in-service training, and laboratory management. Quality control is the study of those errors that are the responsibility of the laboratory and of the procedures used to recognize and minimize them. This study includes all errors arising within the laboratory between the receipt of the specimen and the dispatch of the test results report. On some occasions the responsibility of the laboratory may extend to the collection of the appropriate specimen, the method and time of collection, and the type of collection tube used.