Quest Diagnostics Call us: Call 866-MYQUEST (866-697-8378) Email us: Billing Locations/Appointments Patient Service Centers: Quest Diagnostics Employer Solutions: 1 (800) 877-7484: Quest Diagnostics Nichols Institute Nichols Institute, San Juan Capistrano: 1 (800) 553-5445. Nichols Institute, Chantilly: 1 (800) 336-3718. Nichols Institute, Valencia:.