I live in Chicago IL and I would like to know if anyone can recommend a lab that will perform this test.
There might be a confusion in terminology here. The insulin assay test was developed in the last century by Berson and Yalow, and it is still the standard test for determining serum insulin today.
Dr. Kraft developed what is called the Oral Glucose Tolerance Test (OGTT), which is not, properly a test per se, but is more accurately described as a testing protocol. This protocol involves the administration of a fixed quantity of glucose, and testing insulin at baseline and fixed intervals afterward. The insulin assay test is used to determine the serum insulin levels, which is probably where the confusion originated.
You can ask your doctor to prescribe an OGTT, but be prepared for some resistance. This is a boring and highly labor-intensive procedure, which is why doctors hesitate to prescribe it, and labs hate to carry it out. Because it’s labor-intensive, it is also expensive, and you might have to pay for it out of your own pocket, unless the doctor can make a very good case with your insurance company.