We do NOT look at one single value.
In people and dogs, the insulin level changes every minute.
Your veterinarian is not correct. It is NOT the individual value, but the RATIO of the value in relation to the glucose.
This is the reason an insulin:glucose RATIO is required for this diagnosis.
You can NOT evaluate the insulin level alone, isolated, without the combination of the glucose value at the EXACT time the bloodwork was performed.
The normal range is 70 to 100 mg/dL (or 5 to 20 uL), but again - I am trying to be very complete for you and letting you know that the number itself means very little without comparison to the glucose.