Quest Diagnostics (DGX) is the largest independent research and testing laboratory in the world, holding approximately 14% of the $40 billion laboratory services market. The company provides diagnostic testing, information, and services, for the health care industry, primarily in the United States. Despite having a large domestic presence, Quest also operates in Central and South America and Europe. The company offers routine tests, including blood cholesterol level, blood chemistries, and Pap tests, and esoteric testing services, which includes genetic and immunologic testing, among others. It also provides testing services for clinical trials and risk assessment services for the life insurance industry.

In addition to offering testing services, Quest also manufactures and markets diagnostic and testing equipment for sale to hospitals, other laboratories, physicians, and health insurance companies, to name a few. Quest operates a network of approximately 2,000 patient service centers and principal laboratories, as well as approximately 150 smaller laboratories.

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