Two hour PC (Postprandial glucose test) where they make you fast for 8 hours, take a blood sample to get your glucose reading, and then you eat a meal and then they test your blood-sugar again (another blood sample). You have to do insulin or your sugar goes through the roof. Beats me....it's a stupid test
Oh, I'm used to hearing that referred to as a OGTT (Oral Glucose Tolerance Test). I'm only aware of its use as a diagnostic tool to test first and second phase insulin responses. It's more useful than a fasting blood sugar for diagnosis, because some people still have normal fasting, long after they've developed impaired glucose tolerance, so it catches those people who are pre-diabetic or diabetic sooner. I would have no idea what use it would have for someone who was diagnosed years ago and produces little of their own insulin. Because I've only heard of it being used with newly diagnosed people, I have never heard of people using insulin when they get the test. Are you referring to using your basal insulin (your Lantus?) I would guess you could do that. I'm assuming you would be eating at the doctor's (usually it is a very high carb sugary drink, so they know the exact carb content) and so you wouldn't do your bolus insulin (Humalog) because that would kind of defeat the purpose of the test!
But again I have never heard of this test being done with someone who has been type 1 for many years, I don't get the purpose of it, so I would ask your doctor about your insulin use the day of the test.
Btw if you are having trouble controlling your blood sugars, you might consider changing from a sliding scale which is an older form of dosing, to using an Insulin:Carb ratio. You can get the book Using Insulin by John Walsh which explains this. Or if you want a website with thousands of other type 1's you can talk with, send me a PM.