The GI values of foods must be measured using valid scientific methods. It cannot be guessed by looking at the composition of the food. Currently, only a few nutrition research groups around the world provide a legitimate testing service.
The Glycemic Index Foundation recommends the following laboratories that test to the International Standard (ISO 26642:2010):
AUSTRALIA AND NEW ZEALAND
UK AND EUROPE
Please contact the laboratories directly for costs, requirements and testing timelines as they operate independently of the Foundation.