The results of the curve can be affected by several factors, and measuring the curve at the veterinarian's office can give an inaccurate portrayal of what is occurring at home. Not eating or stress (causing hyperglycemia) may occur at the veterinarian's office. It is advised to feed your cat at home, then take samples until the next meal, in case your cat won't eat at the veterinarian's office.
In addition, it is not uncommon for curves to vary from day to day because many things can affect blood glucose levels such as appetite, digestion, metabolism, exercise, hormones, stress, etc., even in well-regulated cats. Discuss any inconsistencies in your glucose curves with your veterinarian.