Chang is the former director of the Veteran Health Administration's Center for Quality Management in Public Health, which worked to improve patient care through the use of innovative quality management techniques and clinical information systems.

Chang's previous positions include director of the HIV/AIDS program for the Henry J. Kaiser Family Foundation; medical director of the San Francisco Health Plan, a managed health care plan for Medicaid recipients; and director of AIDS Health Services for the San Francisco Department of Public Health, where she oversaw the Ryan White CARE Programs for the city. She also has worked as a medical researcher, examining health disparities in breast cancer care.

She recently served on the Managed Risk Medical Insurance Board, which oversees Healthy Families (the state's Children's Health Insurance Program) and California's Pre-Existing Condition Insurance Plan (from September 2006 to May 2011). Chang continues to practice general internal medicine at San Francisco General Hospital as a UCSF faculty member. She holds a bachelor's degree from Amherst College; a master's degree in public health from the University of California, Berkeley; and a medical doctorate from Columbia University's College of Physicians and Surgeons.