Diabetes mellitus in dogs and catsis a very complicated disease. There is no wonder that pet owners become confused as they begin treatment.
In today’s installment, we will discuss the role of the glucose curve.
Note: most dogs and cats are administered twice-daily insulin. Management of once-daily insulin patients is different in several significant ways. We will discuss those patients in another post.
The purpose of the glucose curve is to determine the duration of the insulin’s action, as well as to help in management of the dosage.
The protocol is to take a blood sample first thing in the morning, usually beginning just before the morning insulin injection. Thereafter, blood samples are obtained hourly (some practitioners stretch this to every two or even every three hours, however, more blood samples means more accuracy). Blood glucose (sugar) levels are obtained through the use of a handheld meter or an in-house blood chemistry machine.
Some veterinarians have pet owners perform blood glucose testing at home if owners are willing and able. The advantage is elimination of any stress that may affect test results.
Glucose readings should go no lower than 90 and no higher than 300 (some experts set the upper limit at 360) between twice-daily injections. The lowest reading of the day is called nadir and the highest is called zenith. Ideally, we would like to have readings between 100 and 200, but we can’t be rigid with that expectation.
An important principle of diabetes mellitus control is that too-low blood sugar can cause death rapidly, whereas pets tolerate high blood glucose for a much longer time period.
Another important principle is that diabetes in people is much more closely regulated than in pets. People may require glucose testing several times each day to accommodate what they eat and how much they exercise. On the other hand, you control your dog and cat’s diet, so they can eat the same carbohydrate-controlled, fat-controlled, high-fiber food day after day. Therefore, whereas people might change their insulin dosage based on a single glucose measurement, that almost never happens in veterinary medicine.
Let’s look at several duration-of-effect scenarios:
- Ideal duration of effect: Ideally, we would like twice-daily insulin treatments to last 12 hours each. That happens in very few patients. If the insulin lasts six to ten hours, control will usually be adequate.
- Too-short duration of effect: In this case, a longer-acting insulin will be needed and/or insulin injections may need to be given more frequently.
- Too-long duration of effect: This might actually be a good thing, as a few pets can actually function well on a single insulin injection daily, using insulins that are twice-daily medications in most pets.
Let’s look at several range-of-readings scenarios:
- Nadir and zenith too high: This is a common finding early in treatment, as we adjust insulin dosage gradually upward to avoid dangerously low blood sugars (see above). In this case, we usually adjust the dosage up in proportion with the discrepancy and retest in a week or two (keeping in mind that every pet is an individual, and the exact next step will depend on that pet’s individual needs and your veterinarian’s recommendations). If the duration of the insulin is satisfactory, the next step may be a fructosamine test, or another glucose curve, according to your veterinarian’s preferences.
- Nadir and zenith too low: This dangerous scenario occurs most commonly when adjustments are made in too-large increments. It can also be seen when an individual pet is uniquely sensitive to his insulin. The insulin dosage will be adjusted downward and another test will be scheduled.
- Nadir and zenith just right: If the duration is also good, this gives us an excellent snapshot of this 12-hour period, but a fructosamine level taken two to three weeks after the last dosage change gives us a big-picture view of the last two weeks, and a much better understanding of diabetes regulation for this patient.
- Nadir not reached: Sometimes, in a given individual, insulin lasts more than 12 hours. In this case we still need to know when the nadir occurs, so testing may continue at home, or at an all-night or emergency hospital. Some of these patients may be candidates for once-daily insulin injections, if the nadir occurs significantly after the 12-hour mark.
Together, the glucose curve and fructosamine monitoring can help to keep your diabetic cat or dog well-regulated.
See you Monday, Dr. Randolph