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As often happens, when looking for something a bit more specific, I came across this image at right, which led me to this webpage:  Laboratory Testing for Diabetes Mellitus.
Curve 1 is a normal OGTT, Curve 6 is a diabetic.  The other causes are listed:
- Hypercorticism - curve 5.
 - Acromegaly - between curves 4 and 5
 - Hyperthyroidism - curve 4.
 - Pheochromacytoma (or "emotional hyperglycemia") - between curves 4 and 5