Rather than ask for a specific test, maybe just say she is a regulated diabetic but still continues to act as if she is starving and continues to use the litterbox like an uncontrolled diabetic. He/she may have ideas of what could be wrong (i am thinking thyroid, but what do I know? Answer: very little

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Phrasing it in such a way lets the vet know you are versed in daibetes and know her blood glucose numbers. Ask if they support testing at home and what kind of diet they recommend - that will give you a idea if you are on the same page.