What Does a Normal Glucose Curve Look Like?

Last week I received an email from one of our clients asking for me to explain what a normal glucose curve looks like. Ha! There are lots of factors that affect a pet’s blood glucose curve. There are pets that have great curves from the start and those (who like a baby who won’t sleep through the night) make pet owners want to pull out their hair. A “good” curve may take some time to achieve as we adjust the insulin dose after diagnosis and possibly down the road. Is there a “normal”?

Assuming a diabetic pet is on a regimented feeding and insulin schedule, we can expect a curve to be mostly the same from day to day. However, if a pet is boarded at a vet clinic for that day the numbers might be higher than usual from stress. If a pet doesn’t eat well while at the clinic, the numbers might be lower than usual. And day to day fluctuations in exercise and activities also affect the numbers even if it is a “typical” day.

In general, a blood glucose level before the feeding and insulin injection will be at some elevated number. That might be 250 mg/dl or it might be at 500 mg/dl. Getting other factors under control that cause insulin resistance and feeding an appropriate food for your diabetic help to have better starting numbers. Clearly the higher the glucose number the greater the clinical signs of diabetes will be. If most numbers were below 200 to 250 (the approximate renal threshold of dog and cat kidneys respectively), we’d not see any overt signs of diabetes in pets.

As the insulin is absorbed and takes effect, the blood glucose number will decrease. Each pet will respond slightly differently to a given insulin. Some may absorb it quickly. Others may take longer. Just know that if a pet responds to the insulin selected, the blood glucose value will decrease some degree for some period of time before it starts to rise again. The reason vets check the glucose every 2 hours (or hourly if it falls below 150 mg/dl) is to see how long the insulin lasts in your pet and to see just how far the glucose drops.

One boo-boo I see many diabetic dog owners make is giving a snack in the middle of the day (partway between scheduled meals and insulin doses). This typically causes the blood glucose level to rise for a couple hours. Cats are strong-minded little monsters that like to nibble throughout the day, so we veterinarians tend to choose long acting insulins for them. Still, if we could convince diabetic cats that they want to eat only twice a day, we might improve their curves. In my home I have a saying, “If kitty ain’t happy, ain’t nobody happy”. I’m still trying to figure out how to get my healthy feline beasts to let me sleep past 5am without sitting on my head, demanding I get up to feed them breakfast.

So, we’ve determined that the glucose is at a high number at the start of the curve then it dips down to some level for some period of time after the insulin injection. Then it starts to rise again, often to the level at the start of the curve. We assume this because we typically feed equal portions and give equal insulin injections twelve hours apart. Again, factors like exercise and sleep may affect the glucose levels during the day compared to the glucose levels at night, but we rarely give a different amount of insulin at an evening dose than at a morning dose.

When we change an insulin dose, we usually wait five to 7 days after a change in insulin dosing before checking another curve. If we do check a glucose during this time it is to check that a pet’s glucose hasn’t fallen too low on a new dose. If we run a curve the day after an insulin dose change, it probably won’t be particularly accurate. Some owners are so eager to get the diabetes under control they raise the insulin dose too rapidly, without their vet’s approval. My grade school band teacher used to say, “Don’t be a Russian and don’t be a dragon.” Approach diabetes in a calm controlled timely manner – no rushing and no dragging.

I hope today’s discussion has helped you understand that there really isn’t a “normal” glucose curve. There are causes and effects to feeding and insulin administration and our goal is to keep most of the glucose numbers below 300 mg/dl and have the bottom of the curve around 100 mg/dl. If we achieve these goals, we will have diabetic pets who aren’t constantly thirsty and famished and peeing nonstop. We will have our pets back to as they were before they were diabetic.

NOTE: Consult your veterinarian first to make sure my recommendations fit your pets special health needs.