Interpreting Glucose Curves

By Dr . Joi Sutton|2016-12-29T15:58:00-05:00Updated: April 10th, 2014|Pet Care, Pet Diabetes, Pet Newsletter|0 Comments

When I first tell my veterinary clients with diabetic pets that I’m going to show them how to check a blood glucose on their pet (so that they can do so at home), I’d say a good number of them get a “deer in the headlights” look. It’s almost as dramatic as the look a client gets when they first contemplate that they will be poking Fluffy with a needle. The fear passes once these good folks see what a tiny needle a lancet has, and what small droplets of blood we can get away with using and still get a good glucose reading.

The next stumbling block is to get them to do glucose curves. Once clients realize that it really isn’t all that difficult to get a glucose reading for most pets, they then need to set aside a day to check the glucose every 2 hours or so. I like checking the glucose hourly if the glucose goes below 150 mg/dl (until it begins to rise again). This means a day spent at home or just running out for a quick errand here and there. The procrastination and dread of running a glucose curve on your diabetic critter is much like how you felt when you were a kid and your mom told you to clean your room.

Today I thought I might enlighten our readers on glucose curves. Maybe it won’t seem like such a chore if you see how much information a curve can give us regarding a pet’s response to a particular insulin and how we use it to make choices about the insulin dose! If you think your pet is well controlled, it feels good knowing if you are right! Or, we might fine tune a fairly well-regulated diabetic pet into a very well-regulated diabetic pet. On the flip side, if Fluffy isn’t doing so well, it’s good to know before a catastrophe occurs.

How long does insulin last?

This depends on the pet’s absorption of the insulin, the pet’s body temperature, the pet’s metabolism of the insulin, and the type of insulin. Some pets do better on one type or brand of insulin than another type or brand. If a pet responds to the insulin but 6 hours later the blood glucose creeps back up to a high number, the insulin may not last long enough to control the clinical signs of the diabetes. How can we know how long it lasts without running a glucose curve now and then? In general, vets tend to choose intermediate duration insulin for dogs (such as Vetsulin, Novolin N or Humulin N) and longer acting insulins for cats (such as Glargine/Lantus or PZI). Demetir/Levemir is coming into vogue for both dogs and cats and is a long-acting, potent insulin. Which is the best first choice for your diabetic? Here is the bit where vets wish we had a crystal ball! Unfortunately, we won’t know how long the insulin lasts and performs in an individual pet until we try it. Typically we will start with a conservative dose of whichever insulin then wait a week and run a curve. We adjust accordingly. Sure, we may do spot checks during that week, but we usually wait a week to run a curve.

How low does the blood glucose go?

The lowest blood glucose reading of the day is called the “nadir”. Knowing the nadir is important because it tells us if we can increase an insulin dose. We vets like the nadir to be somewhere around 100 mg/dl, certainly no less than 80 mg/dl. If some of the blood glucose values during the day are sky high and yet the nadir is low, it means we cannot safely increase the insulin dose for that particular insulin without risking hypoglycemia.

What does a good glucose curve look like?

In general a good blood glucose curve will have most of the numbers under 250 to 300 and bottom out (or nadir) around 100 mg/dl. This makes sense because the kidney threshold for dogs is about 200 and for cats somewhere between 200 and 300 mg/dl. If the blood glucose values are less than the threshold, the pet won’t be drinking and peeing excessively. A good blood glucose curve goes hand in hand with a pet that is clinically “normal”, or nearly so.

What if the glucose curve is disappointing?

Before we go changing to another type of insulin (which can potentially cause a client to have a panic attack knowing how pricey insulin can be), we put on our Sherlock Holmes hat and look for other potential causes of a crummy blood glucose curve. Maybe the postman is slipping Fluffy a bunch of dog treats in the afternoon. Maybe the insulin bottle has been used so long it has cobwebs on it. Maybe Aunt Betsy is giving the injection into the fur instead of under the skin.

Can’t I just check a fructosamine level?

I much prefer blood glucose curves to checking fructosamine levels because fructosamine levels can fool you. Fructosamine levels don’t tell you if the insulin dose is too high which drives the glucose too low which causes a rebound release of stress hormones that cause the blood glucose to rise. This is called the Somogyi swing phenomenon, and can be tricky to identify with a glucose curve and even harder to identify with a fructosamine level. Of course, if you are unable to check a glucose level at home or if your pet becomes very stressed in a clinic setting for your vet to run a curve in the clinic, fructosamine levels can be quite helpful. Fructosamine levels reflect how the blood glucose levels have been on average over the prior couple weeks.

Now that you know what we are looking for does NOT mean you don’t need your veterinarian to evaluate your pet’s blood glucose curve. We read curves and evaluate diabetics all the time. Good diabetes control for your pet is a team effort!

I enjoy interacting with our readers. Feel free to contact me at [email protected].

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

About the Author: Dr . Joi Sutton

Dr. Joi Sutton is a 1993 graduate from Oregon State University. She has practiced both in emergency medicine and general practice. Dr. Sutton has done extensive international volunteer work though Veterinary Ventures, a nonprofit organization that takes teams of veterinarians to undeveloped countries for humane medical care. She also runs a small animal practice in South Florida. Connect with Dr. Joi on LinkedIn

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