Diabetes Mellitus: Part 1
When I started blogging for the clinic, one of the topics that I was asked to write on was diabetes mellitus. I have avoided this for a long time because it is a HUGE topic, but November is diabetes awareness month. So, I will start on diabetes this week, but we will have to continue this another day.
Diabetes mellitus (DM) is an endocrine disease that is caused by a relative or absolute deficiency of insulin, and this results in high circulating glucose concentrations. There are two classifications of diabetes: Type I or insulin dependent DM is characterized by an absolute deficiency of insulin secretion. This is the type of diabetes seen in dogs. Type II or non-insulin dependent DM is characterized by insulin resistance where the insulin does not work well at the cellular level. This is the type of diabetes seen in cats.
Before we go much further, I want to briefly discuss insulin to make sure everyone knows exactly what insulin is and what it does. Insulin is an anabolic hormone in the body that comes from the beta cells in the pancreas. It promotes the uptake of glucose into cells for energy. Glucose is stored in cells in the form of glycogen, which is a highly branched chain of glucose residues, and insulin also promotes the formation of glycogen from glucose, protein, and fats. Insulin promotes fat and protein synthesis, and insulin inhibits gluconeogenesis (this is a pathway that results in the generation of new glucose molecules).
Insulin deficiency results in high blood sugar concentrations because of a decreased uptake of glucose by cells as well as increased production of new glucose. Insulin deficiency also causes fat and protein to be broken down by the body to use as an energy source.
The most common clinical signs of DM are increased water consumption and increased urination. When the blood glucose becomes elevated, the glucose spills into urine, and it draws water with it. To compensate for the loss of water, animals then drink excessively. An increased appetite is another clinical abnormality with DM. Since the cells are starving for glucose, our pets feel hungry, and yet, they frequently lose weight rapidly.
When there is a high index of suspicion of DM, lab work and a urinalysis will be performed. The diagnosis is confirmed by the presence of both an elevated blood glucose AND glucose in the urine. Cats can have a “stress hyperglycemia” where their blood glucose will rise rapidly in a stressful situation such as being restrained for blood collection. However, the blood glucose has to be greater than 250 for a period of time before that sugar will spill into the urine. If there remains a question about the diagnosis, we may need to perform a fructosamine assay. This is a test that evaluates the average glucose for the past 2-3 weeks, and it primarily looks at the amount of glucose attached to albumin (a protein in the body that has a half life of 14-21 days). If you know any diabetic people, they frequently talk about their A1C level. This is a test that looks at an average glucose as well, but it evaluates the amount of glucose attached to hemoglobin (the protein that carries oxygen in your body). Red blood cells live approximately 120 days. This means that an A1C gives an average glucose reading of the past 2-3 months. Obviously, this is an extremely useful test, and unfortunately, it doesn’t work well in our dog and cat patients.
The goals of managing diabetes are similar for dogs and cats. We want to decrease water consumption/urine output, decrease excessive hunger, and maintain a stable weight. This disease requires both insulin therapy as well as dietary management, but how we manage the disease is different in the two species.
Well, I think this is a good place to stop today. We will come back and talk about managing DM in dogs versus cats since there are big differences in between these species. So, stay tuned for our next installments.