Canine and Feline Diabetes - The Somogyi Effect

Canine and feline diabetes is a disease that results in an abnormal increase in blood glucose levels. When treated with insulin, the blood glucose levels are decreased and, hopefully, kept within the normal range.

Insulin overdose, however, is possible and can lead to a phenomenon known as the Somogyi effect.

What Is the Somogyi Effect and How Does It Affect a Diabetic Dog or Cat?

The Somogyi effect occurs when an overdose of insulin occurs. The insulin acts to lower the blood glucose (blood sugar) level. However, because too much insulin was given, the blood glucose level may fall lower than the normal range.

When the blood glucose becomes too low (a condition known as hypoglycemia), the body has defense mechanisms that go into effect to force the glucose to increase again. However, the dog or cat may not be able to control how high the blood glucose goes and it may rebound to an abnormally high level. This is known as the Somogyi effect.

This effect may become circular in its effect if the insulin overdosage is ongoing. When the insulin dose is given, the blood glucose level first falls to below normal then rebounds to an abnormally high level. The insulin dose is repeated, which again leads to first an abnormally low glucose level and then a rebound to an abnormally high level. And the circle goes on and on.

How Is the Somogyi Effect Diagnosed in Dogs and Cats with Diabetes?

A blood glucose curve will be necessary to diagnose this phenomenon. The blood glucose curve is a series of blood glucose measurements taken at regular intervals after the administration of insulin.

When evaluating a blood glucose curve for a dog or cat that is experiencing the Somogyi effect, it will be possible to see the blood glucose value drop first to an abnormally low level and then, if the curve is continued long enough, you will see the blood glucose level going up to an excessively high level.

The existence of the Somogyi effect is one of the reasons that a solitary blood glucose reading cannot be used to evaluate whether a diabetic dog or cat is receiving an adequate dose of insulin or not. A solitary blood glucose reading can fall anywhere between abnormally low to normal to excessively high even if the animal is being overdosed with insulin.

The Somogyi effect is also the reason that fructosamine values must be used with caution in evaluating the progress of a diabetic dog or cat. Fructosamine values represent an average blood glucose value for the dog or cat over roughly two weeks. Because it does represent an average and gives no indication of high low or how high the actual glucose values have gone, the fructosamine level may be normal for a dog or cat that is being overdosed with insulin and undergoing the Somogyi effect.